Mastech MS5308 LCR Tester power adapter issue

[iloveelectronics]

Our fellow forum member John posted an excellent video review a little while ago and it prompted me to order some MS5308's for my shop. Here's his video for those who haven't seen it: http://www.youtube.com/watch?v=9el9mW5woSM

I finally received my first order of MS5308's today. I will be making a post under the Buy and Sell forum soon but before that I'd like to first report what I found with the unit I tested regarding the power adapter issue.

I watched John's video review again, specially the part where he showed the problem with resistance measurement when plugged in with the power adapter. I tried to replicate what he did. So here are my findings:

- At lower reistance, up to about 5k ohms, the power adapter has no effect on the reading at all.
- Starting from near 5k to near 10k, the reading would either jump up or down a little the moment you plug in the adapter, but would soon settle back to the original reading
- From near 10k onwards, the effect becomes more apparent. The reading would not settle to the original value anymore. At 20k ohms, which is what John showed in his video, my unit reads about 19.7k (as oppose to John's 29k or something).
- The drift in the readings becomes more and more significant as the resistance value goes up. At about 470k my unit reads 503k, representing an error of about 7%.

Now, I have no idea if they have partially fixed the problem in this batch sent me, or is it just different behaviours on different units. I will try to contact the manufacturer and see if I can get a response.

[SeanB]

I would say that probably the power supplies are different, and the caps have not died yet inside. If I buy one ( if I see the price from Frankie is irresistible) then I would toss the power supply and replace it with a linear one, simple transformer, bridge and big capacitor and a 7810 regulator on the output side. Then no noise issues with a SMPS unit.

[iloveelectronics]

I will try to see if I can power it with a linear 12V power supply tomorrow. The power jack goes rather deep into the case and I don't have a DC plug with a long enough conductor part to reach it The DC connector they use seems to be specially designed for this unit with sort of a plastic half jacket below the conductor which offers a tight fit into the power jack.

As for pricing I think I will set it at about $177 shipped through registered air parcel with tracking. The going rate on eBay seems to be about $200 minimum. This meter is a beast in terms of weight (almost 3kg including all the accessories and original packaging) so the shipping cost is actually a big part in the equation.

I would say that probably the power supplies are different, and the caps have not died yet inside. If I buy one ( if I see the price from Frankie is irresistible) then I would toss the power supply and replace it with a linear one, simple transformer, bridge and big capacitor and a 7810 regulator on the output side. Then no noise issues with a SMPS unit.

[SeanB]

That makes it close to R2000 when it is here.

As to the power supply i would reuse the original lead in that case.

[iloveelectronics]

I've got news about the power adapter issue directly from the manufacturer (through their sales team). They even showed me what looks like an internal report on the issues (written in Chinese).

To summarize:
1. They are aware of the issues through reports from their customers.
2. Besides the incorrect reading on resistance measurement as shown in John's video review, the power adapter could also potentially fry an IC (they didn't mention which one) and stop the meter from switching on.
3. They acknowledge that it's a design flaw in the power adapter that causes excessive ripples, which leads to the above mentioned problems.
4. The meter functions correctly and within specs otherwise (when on battery power).
5. There's no fix at the moment apart from advising their customers against using the power adapter. For customers with a fried IC they will offer a replacement one with instructions and assistance on how to replace it. The power adapter will no longer be packaged with the meter from now on.
6. They will be working on a redesign and modification in the documentation.
7. After that they will modify based on the redesign all the units that still haven't left the factory.

As a wholesale customer of theirs I will not get any form of compensation apart from some replacement parts if I need them. It sucks. I won't hide it. I received the MS5308's early last week but had been waiting for these official words before I feel comfortable selling, and I must say I'm quite disappointed myself. I guess if I really wanted to pursue it further I could but I don't think I'm going to as I believe the meter is still a good value otherwise, plus I don't really want to ruin the working relationship with Mastech.

Now that their position is clear I will start selling them soon, although I will most likely sell at a slightly lower price than I initially hoped for, and with clear warning to any potential buyer too.

[SeanB]

So when I order one I will just have to ask you to include the adaptor or at least the lead from it, and then I will make ny own. I have a few volunteers from old cordless phone power bricks and will just have to add a voltage regulator to them, along with a new capacitor and a LED power indicator. I did the same for my Uni-T scope, as the supplied wall wart was a PITA to use, the adaptors are all terrible, so it got torn apart and placed in a bigger enclosure.

[iloveelectronics]

No worries, I will still include the adapters as I've already got them in the boxes anyway, but I will just have to warn all buyers of the potential danger of damaging the meter if they are used as-is. New units coming out of Mastech's factory will not include the adapter anymore though. And I was told that the package will remain adapter-less even after the redesign, or maybe it's just an excuse so that don't need to send me any replacement adapters!

So when I order one I will just have to ask you to include the adaptor or at least the lead from it, and then I will make ny own. I have a few volunteers from old cordless phone power bricks and will just have to add a voltage regulator to them, along with a new capacitor and a LED power indicator. I did the same for my Uni-T scope, as the supplied wall wart was a PITA to use, the adaptors are all terrible, so it got torn apart and placed in a bigger enclosure.

[SeanB]

Got any in stock yet?

[retiredcaps]

And I was told that the package will remain adapter-less even after the redesign, or maybe it's just an excuse so that don't need to send me any replacement adapters!

Some business practices and decisions made today by companies reminds me a Mark Twain quote

"Fool me once, shame on you.
Fool me twice, shame on me."

[iloveelectronics]

Got any in stock yet?

Yes, they have been in stock since more than a week ago. I just didn't feel comfortable selling them yet before I knew their official position. I will post in buy and sell later tonight. Selling price will be around $170-ish registered air parcel shipped. That should be at least $30 less than any eBay (or other online shops if you could find them) price you can find. The issues aren't fixed, but I hope the very competitive pricing will make up for it.