MJLorton Solar Power and Electronic Measurement Equipment Forum

Product Reviews => Product Reviews => Topic started by: MJLorton on April 11, 2012, 08:45:57 AM

Title: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on April 11, 2012, 08:45:57 AM
The video review of the UT90C solar powered multimeter is being uploaded now.....I killed it during the review!

I will link to the video as soon as it is up....


Cheers.
Martin.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: Kiriakos GR on April 11, 2012, 03:36:14 PM
Shit happens but the word ....I killed it!  does it translate to damage beyond repair ?

The worst that you can possibly do is to damage the connection of the wires with the solar panel of the dmm. ;)
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: Barryg41 on April 11, 2012, 06:05:32 PM
I checked my Extech 330's manual. It does check Hz% at full mains. Then proceeded to check the mains and worked flawlessly.

Cheers Barry
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: retiredcaps on April 12, 2012, 12:03:03 AM
Great review. 

I think the UT90C should have survived because that is a pretty standard test.  It will be interesting to see if your video makes it to Uni-Trend headquarters to see what their response will be. 

edit: Maybe you will get a replacement multimeter like how Kiriakos got a Fluke 28 II after his 87V was bricked by GSM phone.  Or maybe Uni-Trend will send you an updated board version like Fluke did for the 87V rev 11 to Dave?  Their response will speak volumes about how serious they are in this market.

One minor nit because I ran into this problem last year.

On another forum, I always advise newbies never to use continuity as way to test fuses.  The reason is that some multimeters regard something as continuous if the resistance is less than 1800 ohms.  So if the fuse measures 500 ohms the newbie will be led to believe that the fuse is good.

I have a fuse that will beep continuous on my Fluke, where the threshold is less than 25 ohms, but the fuse is bad because it measures 18 ohms.  A good fuse should measure less than 1.0 ohms.

What is even more confusing is that some multimeters have the diode test and continuity test on the same rotary function (like my Fluke 75).  So instead of displaying an ohms reading for continuity, it displays DC volts.  The same 18 ohm fuse reads 0.009 in continuity test.

This is not a problem on the Fluke 115 as the continuity function shows ohms as a reading.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: retiredcaps on April 12, 2012, 01:03:43 AM
By the way, take the UT90C apart so we can see the front side of the pcb.  Maybe there are some components that you can test and find out what the problem is.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: kodai on April 12, 2012, 03:16:39 AM
I'm very disappointed with this little meter.  Yeah, I can understand the technicality thing on your part of not reading the manual about the switching of ranges while measuring something, but no frequency above 30v?  I've been debating getting that little guy for months, but now that I've how fragile it is I think I'm gonna skip it.  Maybe the next version will improve upon the design.  I mean, I hardly ever work with anything over 30v, so that wouldn't be a real issue for me.  Something about it just seems too fragile to me.  Oh well. 

Great partial review though.  On a side note about you're reference tests:  is your lab at the same temp as the ratting listed on the test boards?  That could throw the tests off a digit or two if its a few degrees off.  Plus the ambient temps in the testing area under your lighting could be warmer still.  Maybe you could tell us your lab temp on each video vs the nominal rated reference board tests.  Of course with all those variables, plus the meters spec sheet over at Uni-T's site show it to be a pretty accurate meter under your partial test. 

Thanks for giving us what little real world info you could on the 90c, it help me make my mind up about it.   :)   
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on April 12, 2012, 04:07:19 AM
I checked my Extech 330's manual. It does check Hz% at full mains. Then proceeded to check the mains and worked flawlessly.

Cheers Barry
Handy feedback...it's a little crazy that we'd have to check the manuals to ensure "general" measurements we are taking are within spec of what the multimeter can do....but this little episode will certainly make me look a little closer at the cheaper meter specs before testing.

Cheers,
Martin.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on April 12, 2012, 04:09:58 AM
Shit happens but the word ....I killed it!  does it translate to damage beyond repair ?

The worst that you can possibly do is to damage the connection of the wires with the solar panel of the dmm. ;)

Indeed it does! I will take a closer look to see if there is anything obvious that can be fixed.....but at lease the cap and solar panel are in one piece ;-)
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on April 12, 2012, 04:23:00 AM
Great review. 

I think the UT90C should have survived because that is a pretty standard test.  It will be interesting to see if your video makes it to Uni-Trend headquarters to see what their response will be. 

edit: Maybe you will get a replacement multimeter like how Kiriakos got a Fluke 28 II after his 87V was bricked by GSM phone.  Or maybe Uni-Trend will send you an updated board version like Fluke did for the 87V rev 11 to Dave?  Their response will speak volumes about how serious they are in this market.

One minor nit because I ran into this problem last year.

On another forum, I always advise newbies never to use continuity as way to test fuses.  The reason is that some multimeters regard something as continuous if the resistance is less than 1800 ohms.  So if the fuse measures 500 ohms the newbie will be led to believe that the fuse is good.

I have a fuse that will beep continuous on my Fluke, where the threshold is less than 25 ohms, but the fuse is bad because it measures 18 ohms.  A good fuse should measure less than 1.0 ohms.

What is even more confusing is that some multimeters have the diode test and continuity test on the same rotary function (like my Fluke 75).  So instead of displaying an ohms reading for continuity, it displays DC volts.  The same 18 ohm fuse reads 0.009 in continuity test.

This is not a problem on the Fluke 115 as the continuity function shows ohms as a reading.

Has to be said....I think I would be very lucky if Uni-Trend did respond in any way as this meter would not be a key focus of many folks...but, having said that, it seems the UT61E has the same limitation...and that would have a larger following. I'll see if I can get some feedback from them.

Thanks for the feedback on the continuity...very valid point. The resistance threshold of the continuity testing has caught my eye in some of the specs but I had not consciously considered the importance...might be a good point to cover in a video....just added it to the "to do" list. 

Thanks for posting,
Martin.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on April 12, 2012, 04:25:04 AM
By the way, take the UT90C apart so we can see the front side of the pcb.  Maybe there are some components that you can test and find out what the problem is.

Yup, will give it a bash...if no joy...I have a good use planned for some of the parts!
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on April 12, 2012, 05:04:31 AM
I'm very disappointed with this little meter.  Yeah, I can understand the technicality thing on your part of not reading the manual about the switching of ranges while measuring something, but no frequency above 30v?  I've been debating getting that little guy for months, but now that I've how fragile it is I think I'm gonna skip it.  Maybe the next version will improve upon the design.  I mean, I hardly ever work with anything over 30v, so that wouldn't be a real issue for me.  Something about it just seems too fragile to me.  Oh well. 

Great partial review though.  On a side note about you're reference tests:  is your lab at the same temp as the ratting listed on the test boards?  That could throw the tests off a digit or two if its a few degrees off.  Plus the ambient temps in the testing area under your lighting could be warmer still.  Maybe you could tell us your lab temp on each video vs the nominal rated reference board tests.  Of course with all those variables, plus the meters spec sheet over at Uni-T's site show it to be a pretty accurate meter under your partial test. 

Thanks for giving us what little real world info you could on the 90c, it help me make my mind up about it.   :)

I don't really work with anything over 30v either but it would leave a nagging feeling inside if I always had to be careful about that limitation....fragile is a good way to describe it!

My goodness....I've come to realise that reference tests, calibration, etc are a hot topic and quite a science.....

We happen to be having cooler weather now so it was about 21C in my "lab" and the temperature the DMMCheck and PentaRef  were calibrated at was 70F (about 21.111C). The documentation quotes as follows: "To maintain 0.01% accuracy, make sure that the ambient temperature is within 14 degrees F (about 7 C) of the calibration temperature. The reference voltage typically drifts approximately 15uV / degree F."

The lighting I have above the test boards is LED so not much heat there...but I'll check that to make sure. The spec of the UT90C in this case is so "coarse" compared to the reference that in this case I was not concerned about environmentals having an effect. But....it is none the less an important point. This becomes more critical with the higher count and accuracy meters and I'm hoping to get another reference source that has a little more flexibility and robustness....so watch this space.

Thanks for posting,
Martin.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: Kiriakos GR on April 12, 2012, 11:22:04 AM
quick note : my first response above, was at the time that the video was not there yet = no video to watch.
I am downloading it now, so to see what really happened.   

About the subject : response of UNI-T
Someone should inform them first, so to get an response.




Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: Kiriakos GR on April 12, 2012, 03:12:47 PM
I am aware that most UNI-T frequency counters on multimeters are limited to 30V of input voltage.
Simply because they were made to count low power signals.

Even my Japanese made dedicated frequency counter (made by LEADER),
Have the specificationsí of 150 MHz, 20V PP Max input.
And it is a great instrument about verifying the accuracy of a PLL synthesizer (low power transmitter). 
The frequency counter circuitry is not protected in any way about over voltage in any device.

The assumption that every multimeter or dedicated frequency counter should be capable to measure frequency of Mains it is a wild one.
But no one can blame an IT specialist because he made such a wild assumption.
   
UNI-T deserves to be blamed because of their tiny in size Users Manuals and the tiny small print in them.
Reading those manuals with the use of binoculars is always a great idea. LOL

Retiredcaps@ 
The violation of written specificationsí usually called as misuse and voids the Warranty.
I can not blame the company if they did not respond.

If the long distance seller haves the good will to replace the device by adsorbing the loss so to keep the customer happy, this is a hypothetical suggestion that Martin should explore too.   

   
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: retiredcaps on April 13, 2012, 01:48:12 AM
I am aware that most UNI-T frequency counters on multimeters are limited to 30V of input voltage.

I don't have any Uni-T's multimeters, but I'm totally surprised at this limitation.  I have NO background or formal training in electronics/electricity at all.

About 6 months ago, I considered getting a UT61E due to the positive reviews, but I managed to find some used Flukes for some very reasonable prices.  Since they are used, I test every function to ensure they work and I use mains to test out the HZ function.

I even had a $50 Amprobe AM-60 with HZ capabilities and plugged the AM-60 into mains without problems.

Quote
The assumption that every multimeter or dedicated frequency counter should be capable to measure frequency of Mains it is a wild one.
But no one can blame an IT specialist because he made such a wild assumption.

Retiredcaps@ 
The violation of written specificationsí usually called as misuse and voids the Warranty.
I can not blame the company if they did not respond.

I agree that the limitation is documented and that this is user error.  However, this is a good opportunity for Uni-T to make their multimeters more robust.  I'm not a multimeter design engineer, but perhaps they can make the HZ fail in a way that doesn't completely brick the multimeter.

I mean we all make mistakes when we are distracted, tired, and/or forgetful so multimeters manufacturers should take this into consideration and try to protect the user and the equipment.

Let's say that Martin did notice the HZ voltage limitation and didn't kill the UT90C, but 3 weeks later he lends this multimeter to a friend and he decides to test HZ on mains.  Does Martin need to put a warning label above the HZ symbol?
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: retiredcaps on April 13, 2012, 03:11:07 AM
Okay, here is something interesting.  The manual for the UT61 series at

http://www.uni-trend.com/manual2/UT61English.pdf

clearly says on page 32 not to have more than 30V input.  This is the same warning as the UT90C.

So why does the UT61D in Dave's $99 shootout part 2 correctly show 50HZ in the mains voltage ohms overload test?  You can clearly see this at 22:12 to 22:37.  You can see him switch from ACV to HZ without disconnecting the mains and the UT61D survived.


Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on April 13, 2012, 04:29:20 AM
Okay, here is something interesting.  The manual for the UT61 series at

http://www.uni-trend.com/manual2/UT61English.pdf

clearly says on page 32 not to have more than 30V input.  This is the same warning as the UT90C.

So why does the UT61D in Dave's $99 shootout part 2 correctly show 50HZ in the mains voltage ohms overload test?  You can clearly see this at 22:12 to 22:37.  You can see him switch from ACV to HZ without disconnecting the mains and the UT61D survived.

Yup, very good point, it clearly worked fine on the UT61D in Dave's test....let me pop a note to Uni-Trend today and see if they can shed some light on the matter. For the price range I think the meters are good...and I love the displays....will feedback if I get any news.

Martin.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: Kiriakos GR on April 13, 2012, 05:50:05 AM
In a Greek forum about electronics, one user did try to measure Hz on Mains with one of those UNI-T meters,
the meter survived but there was no frequensy displayed under his test.
And so he came back on the forum to find ansers about the why the frequensy was not displayed ?

By using a meter out of it spesifications the results about the survival of it, it  is a matter of luck.

The fact that UNI-T does not have any industrial grade multimeters, is mailnly the reason that I am not flaming them about what they do with their line of multimeters for the low powered electronics.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: kodai on April 13, 2012, 12:38:52 PM
So why does the UT61D in Dave's $99 shootout part 2 correctly show 50HZ in the mains voltage ohms overload test?  You can clearly see this at 22:12 to 22:37.  You can see him switch from ACV to HZ without disconnecting the mains and the UT61D survived.

I think that the E has a different LSI  controller than the D.  I know it can do things that the D cant and has features that Uni-T did not enable.  We've all seen the light mod but that come at the cost of the auto-hold feature.  Most users of the E don't even know it has an auto hold because Uni-T has failed to point the feature out in a useful way.  To use it, you have to hold the "hold" button for several seconds. This will launch a countdown timer that gives you about 10 seconds to take your reading at which point it holds whatever you are measuring.  Really odd little auto hold feature.

So maybe the D can measue freq above 30v and/or change measurements while the probes are in place (lets not forget, that may have been the killer as well).  It may be a much more robust meter when compared to the E or most other Uni-T lines. Dont forget that the D could accuratly measure up to 30 Khz when it manual listed the 61's at topping off at 3 Khz.  I dont think that much bandwith is a fluke that Dave just managed to get ahold of.  I think there are major design differences in between the model numbers of their lines and Uni-T has very poorly documented them.  That would be for all the lines including the 90 series.

By the way Martin, did the 90 C's printed manual differ from the 90 A's, or is the manual like the 61 series and one book covers the entire line?
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: retiredcaps on April 13, 2012, 06:08:23 PM
I think there are major design differences in between the model numbers of their lines and Uni-T has very poorly documented them.

Agreed.  From a marketing perspective, if the UT61D and UT61E are so different, they should not have numbered them in the same family of products.  Maybe the UT61E should have been called a UT62 so customers know it uses a different chipset with different specs (20,000 count), etc.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on April 14, 2012, 04:32:40 PM
So why does the UT61D in Dave's $99 shootout part 2 correctly show 50HZ in the mains voltage ohms overload test?  You can clearly see this at 22:12 to 22:37.  You can see him switch from ACV to HZ without disconnecting the mains and the UT61D survived.
By the way Martin, did the 90 C's printed manual differ from the 90 A's, or is the manual like the 61 series and one book covers the entire line?
The manuals for the 90A and 90C are different as they are fairly different in terms of features / functionality i.e. 2000 vs 4000 count, manual vs auto ranging and battery vs solar power.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: Kiriakos GR on April 15, 2012, 06:35:03 AM
Martin did you revive it ?  ;D  (on your latest video it looks that way)

Will  you share the repair tip with the planet ? :)
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: retiredcaps on April 15, 2012, 07:48:05 PM
Martin did you revive it ?  ;D  (on your latest video it looks that way)

I haven't watched the whole video, but at 26:43, Martin says "this the 90C when it was still working" so it looks like he posted the videos out of order.  This is probably not uncommon as he probably had to do a lot of editing.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: retiredcaps on April 15, 2012, 11:07:04 PM
And don't think we haven't noticed that you are color coordinating your shirts with the color of the multimeter rubber holster.  Red shirt for UT90C and orange for your solar clock while talking about the 1272A logging capabilities.  ;)
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on April 16, 2012, 09:44:26 AM
Martin did you revive it ?  ;D  (on your latest video it looks that way)

Will  you share the repair tip with the planet ? :)

I wish I had revived it...still need to pull it apart and will post a video on that and a few clips of the charging before I dinged it.
As per retiredcaps....that video was shot before I did the review.... ;)
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on April 16, 2012, 09:47:46 AM
And don't think we haven't noticed that you are color coordinating your shirts with the color of the multimeter rubber holster.  Red shirt for UT90C and orange for your solar clock while talking about the 1272A logging capabilities.  ;)

LOL....someone told me brighter colours look better on video....I just happened to pull the "right" t-shirt out of the cupboard that day...   ;)
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: Kiriakos GR on April 16, 2012, 02:05:42 PM
And don't think we haven't noticed that you are color coordinating your shirts with the color of the multimeter rubber holster.  Red shirt for UT90C and orange for your solar clock while talking about the 1272A logging capabilities.  ;)

I do not have comments about the t-shirts especially when they do not have the brand logo on them.

But he was hugging the red holsters with an enigmatic joy.
Does he hide anything from us? Time will tell.   ;D ;D ;D
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on April 17, 2012, 06:50:13 AM
And don't think we haven't noticed that you are color coordinating your shirts with the color of the multimeter rubber holster.  Red shirt for UT90C and orange for your solar clock while talking about the 1272A logging capabilities.  ;)

I do not have comments about the t-shirts especially when they do not have the brand logo on them.

But he was hugging the red holsters with an enigmatic joy.
Does he hide anything from us? Time will tell.   ;D ;D ;D
Cheeky man!  :P
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: retiredcaps on April 18, 2012, 04:43:06 PM
One last try?

I watched the follow up video on the UT90C, but I cannot tell what the broken UT90C displays when it is on ohms mode. 

Does it flash 0.0000 or show 0L?
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on April 19, 2012, 07:47:04 AM
One last try?

I watched the follow up video on the UT90C, but I cannot tell what the broken UT90C displays when it is on ohms mode. 

Does it flash 0.0000 or show 0L?

It shows 0.0000 on ohms.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: retiredcaps on April 20, 2012, 02:22:58 AM
It shows 0.0000 on ohms.

I noticed the volts reading is also 0.000.  With your ohms reading 0.000, it almost looks like the input jacks, COM and voltage, are shorted together?

In any working multimeter, if you put the probes together you would get 0.000V and 0.000 ohms (or close to it).  When the probes are apart, you should get a little bit of ghost voltage for volts (minor fluctuation) range and of course 0L for ohm range.

So there might be a shorted component somewhere?  Anyway, if you have time, post the photos.  I will take a look to see if any component is the likely suspect. 
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on April 20, 2012, 05:18:49 AM
It shows 0.0000 on ohms.

I noticed the volts reading is also 0.000.  With your ohms reading 0.000, it almost looks like the input jacks, COM and voltage, are shorted together?

In any working multimeter, if you put the probes together you would get 0.000V and 0.000 ohms (or close to it).  When the probes are apart, you should get a little bit of ghost voltage for volts (minor fluctuation) range and of course 0L for ohm range.

So there might be a shorted component somewhere?  Anyway, if you have time, post the photos.  I will take a look to see if any component is the likely suspect.
Thanks very much for the offer...I'll try get some hi-def photos up over the weekend if possible.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on April 26, 2012, 06:57:19 AM
It shows 0.0000 on ohms.

I noticed the volts reading is also 0.000.  With your ohms reading 0.000, it almost looks like the input jacks, COM and voltage, are shorted together?

In any working multimeter, if you put the probes together you would get 0.000V and 0.000 ohms (or close to it).  When the probes are apart, you should get a little bit of ghost voltage for volts (minor fluctuation) range and of course 0L for ohm range.

So there might be a shorted component somewhere?  Anyway, if you have time, post the photos.  I will take a look to see if any component is the likely suspect.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on April 26, 2012, 06:58:09 AM
It shows 0.0000 on ohms.

I noticed the volts reading is also 0.000.  With your ohms reading 0.000, it almost looks like the input jacks, COM and voltage, are shorted together?

In any working multimeter, if you put the probes together you would get 0.000V and 0.000 ohms (or close to it).  When the probes are apart, you should get a little bit of ghost voltage for volts (minor fluctuation) range and of course 0L for ohm range.

So there might be a shorted component somewhere?  Anyway, if you have time, post the photos.  I will take a look to see if any component is the likely suspect.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: retiredcaps on April 26, 2012, 05:44:45 PM
Okay, I have quick 5 minute test for you to do.

Circled in red is the Volts jack.  Circled in black is the COM jack.  Circled in blue are diodes (5 total).  Circled in yellow are transistors (3 total).

All tests can be done "in circuit". That is, there is no need to desolder unless the readiings indicate they may be shorted.

1) Test the diodes with the diode test function of a working multimeter.  As you know a good diode should read between 0.4 and 0.8V one way and "out of range" the other way.

A shorted diode will probably reading the same voltage both ways (something low like 0.2V both ways).

2) Test the transistors with the resistance function of a working multimeter.  Number the transistors pins 1, 2, and 3.  Measure the resistance between pins 1-2, 1-3, and 2-3.

An ohms reading of less than 30 ohms suggests a shorted transistor.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on April 27, 2012, 09:06:12 AM
Thanks.....

I did the checks on the diodes....all ok.

Then I did the checks on the transistors....and got very excited....there was a short on 2-3 or 1-2 depending numbering sequence....on all of them...

I pulled out some new NPN transistors to do an "out of circuit" test to confirm I had it right....and yes...no shorts there.

I preceded to warm my soldering iron to remove and replace the 3 transistors....when I noted they are shorted on the underside of the board with solder...????

See attached picture.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: retiredcaps on April 27, 2012, 06:51:19 PM
It is a little difficult to see due to the low resolution of the photos if they are soldered together, but I believe you.  What are the part numbers on the transistors?  I'll take a look at the datasheets to see why they may be soldered together?

By the way, here is another way to test those transistors using the diode test function (34 second video)

http://www.youtube.com/watch?v=8VK_4gZU__I

You may want to test those 3 transistors again using the above method and on a couple of new transistors.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on April 29, 2012, 05:45:54 AM
It is a little difficult to see due to the low resolution of the photos if they are soldered together, but I believe you.  What are the part numbers on the transistors?  I'll take a look at the datasheets to see why they may be soldered together?

By the way, here is another way to test those transistors using the diode test function (34 second video)

http://www.youtube.com/watch?v=8VK_4gZU__I

You may want to test those 3 transistors again using the above method and on a couple of new transistors.
Thanks very much, that video put the transistor testing with the diode function into perspective staight away. The NPN's on the board have a different pin out to the ones I was using as a reference. I'm about to de-solder one of the transistors so I can test it out of circuit and will feedback.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on April 29, 2012, 06:20:01 AM
I removed the transistors from the board and tested between base, emitter and collector and a 0.7 voltage drop showed correct operation. No shorts.

I show the pads they were removed from and you can see how the 2 pins of each transistor were shorted.

Pity!! I thought we might find the fault....but I learnt something through the process so thanks very much for the guidance. 
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: retiredcaps on May 10, 2012, 12:25:19 AM
I just watched your test a transistor and diode video.  Great job.

If you are willing to test a bit more, take a high resolution picture of the components underneath the lcd.  I can look for their datasheets and see if any of the ICs are shorted.  Sometimes VCC will be shorted to GND. 

I have more ideas, but obviously since I don't have the board in front of me, I can't just test things when I want to.

BTW, I ran into some Sperry brand multimeters.  Sperry is a known name in North America.  Their multimeter suspiciously look like Uni-Ts.  Even the manuals have the same 30V maximum "warning" when measuring frequency.

http://www.sperryinstruments.com/product/digital-multimeters

Hmm, does this screen look familar?

http://www.sperryinstruments.com/images/applications/dm6400_2_lg.jpg
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on May 10, 2012, 07:02:54 AM
I just watched your test a transistor and diode video.  Great job.

If you are willing to test a bit more, take a high resolution picture of the components underneath the lcd.  I can look for their datasheets and see if any of the ICs are shorted.  Sometimes VCC will be shorted to GND. 

I have more ideas, but obviously since I don't have the board in front of me, I can't just test things when I want to.

BTW, I ran into some Sperry brand multimeters.  Sperry is a known name in North America.  Their multimeter suspiciously look like Uni-Ts.  Even the manuals have the same 30V maximum "warning" when measuring frequency.

http://www.sperryinstruments.com/product/digital-multimeters

Hmm, does this screen look familar?

http://www.sperryinstruments.com/images/applications/dm6400_2_lg.jpg

Thanks very much...but certainly inspired by your guidance and assistance.

What a laugh...Sperry...certainly a re-branded UNI-T....I'd love to make a study of how all the re-branding in different industries works....can be very confusing to Joe public and often a money spinner....

Ok...let me get a good picture taken of the bits under the LCD and I'll post it soon.

Cheers,
Martin.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on May 11, 2012, 08:30:47 AM
Here we go.......but take a look at the caps along side the IC....I think they look a little suspect?? Only noticed them in the pictures when posting this...
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: retiredcaps on May 11, 2012, 07:19:24 PM
Here we go.......but take a look at the caps along side the IC....I think they look a little suspect?? Only noticed them in the pictures when posting this...

1) The cap sleeves look all melted somehow. 

2) I found the datasheet for FS9721_LP3.  I'm reading it now to try and understand how it works.

3) While I do that, I have 3 more things for you to measure.  All are resistance readings.

i) Marked in yellow are PTCs.  I believe they should all be around 1K ohm from reading the datasheet.  You may have to desolder these 3 to get a accurate reading?

ii) R26 (in blue) should be a 10M ohm resistor.  Measure this in circuit and verify that it 10M.

iii) R31 (in red) is a 10K SMD resistor.  Measure this in circuit and verify that is 10K.

4) BTW, rumor has it that the Fluke 15B and 17B use the same FS9721-LP3 processor.  Certainly the specs for the Fluke 15B and 17B match up with the FS9721-LP3 datasheet.

5) A really good SMD soldering video is here

http://www.youtube.com/watch?v=3NN7UGWYmBY

6) Of course Dave Jones also has a 3 part soldering video and demonstrates various techniques for SMD.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on May 14, 2012, 04:00:52 AM
Here we go.......but take a look at the caps along side the IC....I think they look a little suspect?? Only noticed them in the pictures when posting this...

1) The cap sleeves look all melted somehow. 

2) I found the datasheet for FS9721_LP3.  I'm reading it now to try and understand how it works.

3) While I do that, I have 3 more things for you to measure.  All are resistance readings.

i) Marked in yellow are PTCs.  I believe they should all be around 1K ohm from reading the datasheet.  You may have to desolder these 3 to get a accurate reading?

ii) R26 (in blue) should be a 10M ohm resistor.  Measure this in circuit and verify that it 10M.

iii) R31 (in red) is a 10K SMD resistor.  Measure this in circuit and verify that is 10K.

4) BTW, rumor has it that the Fluke 15B and 17B use the same FS9721-LP3 processor.  Certainly the specs for the Fluke 15B and 17B match up with the FS9721-LP3 datasheet.

5) A really good SMD soldering video is here

http://www.youtube.com/watch?v=3NN7UGWYmBY

6) Of course Dave Jones also has a 3 part soldering video and demonstrates various techniques for SMD.

Thanks very much for this, I will tackle the testing later in the week...a little busy at the moment.

I'll  take a look at the video and follow-up on Dave's videos...I thought he might have something on that topic.

Cheers,
Martin.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: Administrator on May 19, 2012, 08:48:05 AM
Here we go.......but take a look at the caps along side the IC....I think they look a little suspect?? Only noticed them in the pictures when posting this...

1) The cap sleeves look all melted somehow. 

2) I found the datasheet for FS9721_LP3.  I'm reading it now to try and understand how it works.

3) While I do that, I have 3 more things for you to measure.  All are resistance readings.

i) Marked in yellow are PTCs.  I believe they should all be around 1K ohm from reading the datasheet.  You may have to desolder these 3 to get a accurate reading?

ii) R26 (in blue) should be a 10M ohm resistor.  Measure this in circuit and verify that it 10M.

iii) R31 (in red) is a 10K SMD resistor.  Measure this in circuit and verify that is 10K.

4) BTW, rumor has it that the Fluke 15B and 17B use the same FS9721-LP3 processor.  Certainly the specs for the Fluke 15B and 17B match up with the FS9721-LP3 datasheet.

5) A really good SMD soldering video is here

http://www.youtube.com/watch?v=3NN7UGWYmBY

6) Of course Dave Jones also has a 3 part soldering video and demonstrates various techniques for SMD.

Ok...here we go:

PTC1: 1K
PTC2: 567 ohm...out of circuit
PTC3: 589 ohm...out of circuit
R26: 100 ohm...out of circuit
R31 SMD: 10 M ohm...checked several times...

I watched Dave's soldering tutorials....very helpful...I have now acquired a solder station so I'm setting up for the SMD work soon.


Thanks again...

Cheers,
Martin.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: retiredcaps on May 19, 2012, 11:31:57 PM
PTC1: 1K
PTC2: 567 ohm...out of circuit
PTC3: 589 ohm...out of circuit
R26: 100 ohm...out of circuit
R31 SMD: 10 M ohm...checked several times...

Okay, I'm using this datasheet as a reference.

www.ic-fortune.com/upload/Download/FS9721_LP3-DS-20_EN.pdf

With the above, I was using the datasheet's pcb designators (page 19) as described by the various diagrams/figures, but it looks like the UT90C is using a variation.

R31 is good as your 10M ohm resistor.  As long as R26 matches the color code for a 100 ohm resistor, it is good.

PTC1 at 1K is good.  PTC2 and PTC3 are lower than what I expected (1K) unless they are in series, but I don't think the low values are the cause of the UT90C not working.  If one of the PTCs were completely open, then it might explain why the UT90C is not working.

Let me think about this for a few more days.  Unless I spot something obvious, I think the FS9721-LP3 might be bad.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on May 21, 2012, 03:14:53 AM
PTC1: 1K
PTC2: 567 ohm...out of circuit
PTC3: 589 ohm...out of circuit
R26: 100 ohm...out of circuit
R31 SMD: 10 M ohm...checked several times...

Okay, I'm using this datasheet as a reference.

www.ic-fortune.com/upload/Download/FS9721_LP3-DS-20_EN.pdf

With the above, I was using the datasheet's pcb designators (page 19) as described by the various diagrams/figures, but it looks like the UT90C is using a variation.

R31 is good as your 10M ohm resistor.  As long as R26 matches the color code for a 100 ohm resistor, it is good.

PTC1 at 1K is good.  PTC2 and PTC3 are lower than what I expected (1K) unless they are in series, but I don't think the low values are the cause of the UT90C not working.  If one of the PTCs were completely open, then it might explain why the UT90C is not working.

Let me think about this for a few more days.  Unless I spot something obvious, I think the FS9721-LP3 might be bad.

I tried going to that link but I get a warning that it's an "attack page"....and might steal my data....odd...

Thanks again for your efforts. I thought it might be something in the main IC....but I would have thought that if that had gone faulty the meter would not display anything "intelligent" at all. I presume it can have a partial failure?

Cheers,
Martin.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: retiredcaps on May 21, 2012, 11:52:24 PM
I tried going to that link but I get a warning that it's an "attack page"....and might steal my data....odd...

Thanks again for your efforts. I thought it might be something in the main IC....but I would have thought that if that had gone faulty the meter would not display anything "intelligent" at all. I presume it can have a partial failure?

I'll study the datasheet some more.  I do have a "cheap" multimeter here that I can take apart and study to see what is going on and that may help with your UT90C.

I also got the same virus warning, but I checked the pdf with multiple AV software and it is clean.  I tried to attach the pdf and a zipped copy of it, but the file can only be 300KB and the zipped is 1.1MB.

Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: retiredcaps on June 03, 2012, 12:05:39 AM
I found this while looking for some info

http://www.amazon.co.uk/VOLTCRAFT-Voltcraft-VC290-DMM/dp/B003A5UGBA

I found this part of the description particularly LOL

"The device is protected with comprehensive safeguards against misuse."
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on June 04, 2012, 06:32:25 AM
I found this while looking for some info

http://www.amazon.co.uk/VOLTCRAFT-Voltcraft-VC290-DMM/dp/B003A5UGBA

I found this part of the description particularly LOL

"The device is protected with comprehensive safeguards against misuse."
I love it!! I read the entire advert....the "English" is certainly entertaining....
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: retiredcaps on December 29, 2012, 03:45:58 AM
Hey Martin,

I was thinking about your UT90C again and thought you might be inspired by one member's recent blog site.  His site is full or repairs and pictures.  Highly recommended.

http://mrmodemhead.com/
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on December 29, 2012, 07:43:52 AM
Hey Martin,

I was thinking about your UT90C again and thought you might be inspired by one member's recent blog site.  His site is full or repairs and pictures.  Highly recommended.

http://mrmodemhead.com/

Brilliant site Mr Sharp Eyes! I've linked to it from my channel page and hope to make some time to go through it.
I'll drop Mr Modemhead a message too.

Thanks.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: ModemHead on December 29, 2012, 09:31:42 AM
Wow. A whole thread about a broken multimeter and somehow I missed it...   :-[
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: retiredcaps on December 29, 2012, 05:47:58 PM
Martin,

I may have more test suggestions for you just to confirm that the FSP 9721 on the UT90C is indeed fried. 

I have an UEI multimeter that is not working properly and it uses the FSP 9711 chip.  I think the two are close enough to make comparable readings on certain pins.  It is an on/off project for me as I discover new testing techniques or learn more about how the chip works in general.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: ModemHead on December 29, 2012, 08:55:15 PM
Just thought I would throw in my 2 cents worth...

I looked at the datasheet 'common use' circuit to see how the Hz measurement function was implemented. There is no guarantee that the Uni-T engineers followed this exactly, but in the absence of a more accurate schematic, it's all we have to go on. In any case I would not expect the component designators to match.

(http://mjlorton.com/forum/index.php?action=dlattach;topic=24.0;attach=962;image)

For Hz mode, J9, J6, and J8 would be jumpered by the function switch, providing an AC-coupled path through C15 straight to the ADP input of the DMM IC.  Q1, Q2, and the 1K PTC are supposed to provide over-voltage protection for Hz, Ohm, Cap, and Diode functions.

Base-emitter junctions of transistors function quite reliably as zener diodes when reverse biased, especially when the base-collector junction is taken out of the equation by shorting it out. Note that Q1 and Q2 are in this configuration and are back-to-back, in series.  The B-E reverse breakdown voltage is probably about 5V, and the B-E forward voltage is around 0.7V as usual.  So regardless of the polarity of the input voltage, the drop across the two Qs should never exceed about 5.7V.  A bidirectional voltage 'clamp'.

That means that point 'X' in the diagram should be limited to +/- 5.7V.  If a higher voltage is applied, it will be dropped across the PTC thermistor, and current will increase through the PTC and the clamp transistors (green path).  As the voltage drop grows, the thermistor will heat up and its resistance will increase, limiting the current and dissipating the excess energy.  That's how it should work, but something went wrong.

Q1 and Q2 are switched out for voltage measurements, so even if they failed short it should not affect voltage functions.  About the only scenario I can come up with is that the PTC opened up permanently.  Or, given that the Hz function feeds the ADP input almost directly, the DMM IC is fried. :(
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: retiredcaps on December 30, 2012, 03:02:53 AM
Q1 and Q2 are switched out for voltage measurements, so even if they failed short it should not affect voltage functions.  About the only scenario I can come up with is that the PTC opened up permanently.  Or, given that the Hz function feeds the ADP input almost directly, the DMM IC is fried. :(

Hi ModemHead,

Thanks for giving a play by play on the schematic and input protection.  Interpreting schematics is one area I'm weak in and appreciate the full detailed explanation.

I had Martin pull and test all the 3 pin transistors and they all tested fine.

The PTCs seem to test okay?  Martin reported

PTC1: 1K
PTC2: 567 ohm...out of circuit
PTC3: 589 ohm...out of circuit

I have no idea what a good PTC should measure other than relying on the FS9721 datasheet values (that is 1K).  So PTC2 and PTC3 could be bad or they could be used together in series (giving it a 1K value)?

For my own learning, I decided to measure the DC voltage on pins 26 (TENM) and 24 (ONEM).  I found two points on my UEI board that fed into the above pins making it easier to measure.

Since I don't have a variable DC power supply, I got 4 semi-dead 9V batteries and noted the following:

9V battery voltage     TENM     ONEM
8.08v                  80.7mv   0.0
4.90v                  52.6mv   0.0
3.76v                  37.5mv   0.0
2.466v                 228mv    228mv

Now my UEI display is stuck on "all segments" test, but what I'm trying to show with the above testing is that the input voltage divider is working by measuring pins TENM and ONEM.  My UEI has two PTCs.

So if Martin does this same test, he can verify that the input section is working up to the FSP9721 (implying that the PTC works)?

Martin, to test this (probably 15 to 30 minutes of your time)

1) Use your variable power supply to supply DC voltage to the input jacks of the UT90C.
2) Use a working multimeter to measure the DC voltage at pins TENM and ONEM.
3) The black probe on the working multimeter goes to the UT90C COM jack for ground.
4) The red probe goes on TENM and ONEM (or some physically bigger component that feeds these pins to make probing easier - looking at your photo, I can clearly see traces leaving pins 26 and 24).
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: ModemHead on December 30, 2012, 09:22:49 AM
Sorry, I think I blew the margins in this thread with my diagram...

PTCs: Those values look OK to me.  The actual PTC resistance generally isn't important because it is very small with respect to the impedance of the rest of the circuit (1K vs 10Meg+).  Another way of saying that is that the normal current through the PTC is so small that the voltage drop on the PTC is negligible.

Speaking of high impedances, notice that the TENM pin on the chip is connected through a 10Meg resistor.  This is the 'top' end of the voltage divider.  Using internal CMOS switches, the micro-controller in the chip (under control of the auto-ranging algorithm) will tie this point to one of the other precision resistors, which you can see are grounded when the meter is in voltage mode.  That makes the 'bottom' of the voltage divider, which is capable of dividing by 10, 100, 1000, and 10,000.

Depending on how the divider is configured, adding the 10Meg impedance of another DMM at the TENM pin can actually affect the voltage there significantly.  So voltages measured there may not make sense at first glance.  Observer effect...

Note that in your measurements, TENM and ONEM were the same voltage for 2.466V input. That means the divider was in 1/10 mode.  I assume the divider was in 1/100 for the higher voltages (HUNK would be in use instead of ONEM.)  As the ratio goes up, the bottom resistor gets smaller and your 10Meg DMM has less effect.

Your test plan is valid, but I think the easiest place to verify all input circuitry (inc. PTCs) would be to locate point 'X' on the circuit board.  It should be on side of the 10Meg input resistor not connected to the DMM IC.  And it should reflect exactly (1:1) whatever voltage is applied to input jacks.  The voltage divider resistors can be verified separately with the power off if necessary.

Hope this helps...
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: retiredcaps on December 30, 2012, 04:06:58 PM
Note that in your measurements, TENM and ONEM were the same voltage for 2.466V input. That means the divider was in 1/10 mode.  I assume the divider was in 1/100 for the higher voltages (HUNK would be in use instead of ONEM.)
So for my own learning again, I went and measured the HUNK

9V battery voltage     TENM     ONEM     HUNK
8.08v                  80.7mv   0.0      80.0mv
4.90v                  52.6mv   0.0      52.4mv
3.76v                  37.5mv   0.0      36.7mv
2.466v                 228mv    228mv    0.0

The "4.90v" battery above measures around 5.431V today. 

It is obviously dead because the top and the bottom are both bulging.  The expiry date on it is Mar 2004.  I think I got it from buying an used multimeter which is why I always check the battery of any electronic device before I use it.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: ModemHead on December 31, 2012, 12:36:03 AM
So for my own learning again, I went and measured the HUNK
With those measurements, I think you have proven that the micro-controller is running and performing its auto-ranging task properly.  Which implies that it is getting good information from the A/D converter.
Title: Re: UNI-T (UNI-Trend) UT90C review.....I killed it!
Post by: MJLorton on January 02, 2013, 06:14:38 AM
Brilliant input gents...thanks very much.

I'm just busy on my DC load project and hope to have time after that to have a fiddle with the UT90C.

Cheers.