Looking for Metex 4500H service documentation

[ttp]

Decided to bring my 22 year old Metex 4500H out of retirement. Has been working great, then stored on the shelf for few years (battery taken out). Now doesn't give any signs of life when swithed on. Would appreciate if someone could point me to service documentation of any kind.

[Kiriakos GR]

I have the feeling that some one else tried to use it when you was away, and killed it.
I have never see a Metex service manual, I do not think that they share them even if they have them as company.

[ttp]

You are right Kiriakos, I googled a bit but haven't seen any either. Have sent them email but no reply so far...

[retiredcaps]

Take it apart and see what chip set it uses.  If the Metex 4500H is a 2000 count meter, it may use the popular 7106.

Also post a picture of the internals.  There may be a leaky capacitor or some corrosion on the pcb even without the battery installed.

I can't read a schematc to save my life right now, but I can suggest test points in the multimeter once you post a picture.

PS.  I have a Metex M-3610 that doesn't zero.  Details at

http://www.eevblog.com/forum/chat/metex-m-3610-repair-help-dmm-won't-zero-properly-in-ohms-and-dc-volts/

I have been doing other projects so I haven't spent any serious time working on it.

[ttp]

Thanks for tips. I had it apart and couldn't spot anything wrong on PCB. It uses ICL7129, still in production if it died. Once I get back home I'll have another look, can't be to hard as the display is blank and there are only few components and main IC that could be responsible.

[ttp]

Retiredcaps, got some photos and some good news.

I connected the battery and was having a look at the meter (without the case at this stage), nothing really happen but I left it powered on for a while. My thought was there are few electrolitycs there, they may need voltage applied to rebuild their insulation layer (the meter was unused since sometime in the 90's, in 2009 I briefly powered it but since it didn't show anything I put it back in the box).

After few hours I started to see very faint digits on LCD. Now, about 3 days later LCD display is very readable, certainly improved a lot and it is usable. Not as intesive as it was originally but maybe the intesity will come back to original state... Not sure if its the effect of LCD aging or not being used for years but I hope it will keep on improving.

Since I got display working I could do some tests and DC voltage, DC current and resistance (including continuity) work very well. Actually I could only test DC volts and it is very accurate but I'm confident current and resistance are ok.

AC voltage and current show over-range on any range including 1000V or 10A. Looks like AC-DC rectifier/converter is faulty, I will start with desoldering 4 or 5 small electros around that circiut. There is also one poliester cap with funny stuff on its surface, it will be replaced as well. After X-mas I'll have a chance to look under magnifying glass and with soldering iron around.

I'm not sure about quality of the photos as I'm in a bright sunny environment and cannot find a place dark enough to see camera or laptop screen very well... Hope you can see the photos all right.

[retiredcaps]

My thought was there are few electrolitycs there, they may need voltage applied to rebuild their insulation layer (the meter was unused since sometime in the 90's, in 2009 I briefly powered it but since it didn't show anything I put it back in the box).

After few hours I started to see very faint digits on LCD. Now, about 3 days later LCD display is very readable, certainly improved a lot and it is usable.

I'm working on fixing an old 30 Fluke.  Unfortunately, at least 2, possibly more capacitors have already spewed out their electrolyte and caused some collateral damage.

I'm planning a complete recap if/when I found out what the problem is.

I bought this multimeter used so I have no idea when/how it was used/abused.

[ttp]

Could not upload any more photos, I've resized them down a bit and try now...

[ttp]

Chemical spills on PCBs are not nice, seen few of them in old calculators left in drawers/storage with batteries iside the unit...

[SeanB]

First clean off all that flux residue on all the boards, and take the display off and clean the zebra strip with water ( do not do anything to the display other than wipe the contacts with a dry lint free cloth) and let it dry thoroughly. Take the IC out of the socket and reinsert it about 5 times to clean the pins. Solder the dry joint on the daughterboard connector and then clean the switch contacts and lubricate them. That will take care of the intermittent display ( probably backplane is high resistance in the zebra strip) and should help with any other non component troubles.

[Kiriakos GR]

I do not see how one bath it can cure damage on components.
And also why to take apart the display when there is no power ?
This meter needs point to point troubleshooting from the 9V clip all the way up to the power switch. (as first step)

[ttp]

Hi Kiriakos, the meter started working all by itself. It looks like AC ranges are still broken but DC volts, current and resistance seems to work fine. The display is not 100% intense but its reasonably ok.

[ttp]

SeanB, I will clean the PCB but since the meter was working very good for a number of years in the past in current condition I want to leave cleanup till last. I want to find out what broke the AC measurement first and fix it, then will resolder and clean up flux, possibly recheck/recalibrate the meter. Possibly next week when I'm back home and have all my tools. At the moment just looking at PCB, chasing the tracks and working out which components do what.

[ttp]

Good news! It is working good again including AC voltage and current ranges. Been in holiday mode for a while and then busy but finally I got around to order replacement electrolytic caps and fitted them last night. The meter works fine now on all ranges including AC.

Just a quick photo showing DC voltage measurement -  the meter reads 5.05V against reference of 5.0002V. This is 0.1%out, which is Metex's claimed accuracy for DC voltage - not bad for 25 years old meter that has never been calibrated since new.

I'll likely post more photos in the future and maybe calibrate the meter against my Fluke.

One lesson I've learned is never put your test gear away in storage - keep using it and it will keep working.

[MJLorton]

Excellent news! Thanks for the updated post.