Metex M-3610 repair help - dmm won't zero properly in ohms and DC volts

[retiredcaps]

I got this Metex M-3610 for free.  It looks like it was made in 1987.

Unfortunately, it doesn't zero when I touch the probes together on DC voltage.  It reads about 0.250Vs when the probes are not touching.  When I measure a 9V battery, it reads 0.63V even though it is a new battery.

On resistance mode, the multimeter correctly shows "1" or out of range when the probes are not touching, but when I touch the probes together, I get 25 ohms.

I have tried known good probes and fresh akaline batteries so I'm sure the problem is with the M-3610 itself.

It uses the IC7106 chip and in the datasheet at

http://pdf1.alldatasheet.com/datasheet-pdf/view/177757/INTERSIL/ICL7106CPLZ.html

it talks about AN032 "Understanding the Auto-Zero and Common Mode Performance of the ICL7136/7/9 Family", but for the life of me, I cannot find the datasheet/app note anywhere.

I'm assuming my problem is with the auto-zero function, but without the app note, I'm not sure what exactly to test.

Suggestions would be appreciated.  I know this multimeter isn't worth much, but I want to learn more about electronics and this is a great opportunity.

PS. Now I know why Dave Jones hates those 9V wires.  I managed to damage the red wire when snapping back the case on.  I didn't see it trapped between the case and screw hole when I put the front cover back on.   

[amyk]

That looks like the ancestor of the infamous DT-830 series.

Apart from checking to see if any components have drifted out of spec, the only other culprit is the '7106 itself.

[retiredcaps]

That looks like the ancestor of the infamous DT-830 series.

Yes, I had the same thought when I saw the 7106 chip.  At least I have your Elenco kit instruction manual allow with the 7106 datasheet to give me some idea how it works. 

Apart from checking to see if any components have drifted out of spec, the only other culprit is the '7106 itself.

Well, there aren't too many components so I guess I will start checking in circuit first and anything that looks suspicious will warrant desoldering and retesting out of circuit.

Thanks again for your input.  It is appreciated.

[retiredcaps]

FYI.  More rebadged dmm!!  Saw this thread and watched the video. 

https://www.eevblog.com/forum/general-chat/fake-transistors-!-never/

I noticed that the SkyTronics 600.527 is identical to the Metex M-3610 (made in 1986).

[wkb]

   That is the same multimeter as one in my collection.  Mine still works just fine btw.