Solartron 7061 7.5 digits DMM -- some questions before repair attempt

[rodd]

Dear All,
I happened to put my hands in one of these beasts which seems to be in very good condition.
It passes self test and initialize properly, I think (see att 1)
Unfortunately the reading is very wrong, so I will try to repair it (att 2)
The PCB's are in very good shape, so I think no one has tried to mess with this instrument before (att 3)
My questios are:
1 - The configuration dip switch that is described in the manual has 6 contacts but the one installed in the board just 4.
I could not find a adjustment recomendation for it (near front panel in att 3)
2 - Some of the large caps are dated 1987, and one has a 5308 date code. (att 4 and 5).
Now the recurring question in this forum: Should I replace them?
3 - I can't find any date code in the small electrolytics.
Are they always printed? Should I replace them?
4 - The battery voltage is 2.4V and there are signs of corrosion near it.
I  could only find NiMH replacement here in Brazil.
Can use one of them?
Can this low voltage explain the false readings?
Thanks,
Roger

[Kosmic]

Start at the input and follow the signal path. You should find the problem before you reach the integrator.

I repaired a 7061 with similar symptoms. In the end the problem was the input selector switch. I cleaned it with deoxit d5 and was working fine after. Was probably just a little bit dirty.

You should find some pads around the switch to test continuity.

[Kosmic]

Also I tested all the electrolytic cap from 2 units made in 1988 and they were all in good shape with low ESR.

For the battery, both of my unit already had NiMH. I used this one from ebay:

https://www.ebay.com/itm/1-pc-x-New-Rechargeable-3-V150H-3-6V-160mAh-Ni-MH-Backup-Battery-With-3-Tabs-/222674552150?redirect=mobile

[coromonadalix]

It would say   do one thing at the time

Follow signal paths, try to find the problem source,   when the meter eventually will work, change the caps section by section if needed,   check all voltages points with a meter and with a scope if you have one,  you'll see noise / ripple currents if they dont do their job

some manuals
http://bee.mif.pg.gda.pl/ciasteczkowypotwor/Solartron/Solartron_7061_Voltmeter_Operating_Manual.pdf
https://www.opweb.de/en/model.php?id=10069
https://elektrotanya.com/solartron-schlumberger_7061_systems_voltmeter_1986_op_sm.pdf/download.html
https://www.download-service-manuals.com/en/manual.php?file=Schlumberger-7389.pdf


Maybe this one ?
http://doc.xdevs.com/doc/SOLARTRON/Solartron_7061_7062_7.5_Digits_Systems_Voltmeters_Service_Manual.zip

Or at K04BB,       if you search solartron, you have lots of eeproms dump too.
http://www.ko4bb.com/getsimple/index.php?id=download&file=06_Misc_Test_Equipment/Solartron/Solartron_7061_7062_7.5_Digits_Systems_Voltmeters_Service_Manual.zip

A thread here
https://www.eevblog.com/forum/reviews/solartron-7061-help-and-come-photos/

[grizewald]

If the onboard battery has leaked, remove it from the board and make sure that you neutralise any alkali that has leaked onto the PCB. You should use a dilute solution of white spirit vinegar and water and lots of it with plenty of scrubbing. Check the solder resist near any leaks as the alkali from the battery creeps under the solder resist and continues to eat away at the PCB unless you deal with it.

I am currently repairing a Solartron 7151 where the same thing happened. The damage is extensive, particularly nasty is the fact that the alkali gets into the vias and eats them away from the inside. The only outward sign is that the solder has turned grey and is almost impossible to melt. If you check for conductivity from one side to the other, it will be open circuit. Then the fun begins with trying to clear the via so you can repair it with a wire from one side to the other.

It all adds up to many hours of fun peering down a microscope and scraping, cleaning, scraping, cleaning. 

[coromonadalix]

err  some damadge indeed

[rodd]

Hi Folks,
Thank you for the replies.

I started by checking the power supplies voltages and they are ok, except by:
1 - the +5Vc (TP-503) is reading 4.4V, probably because the aged battery)
2 - the  +40V unreg (TP-505) is reading 38.6V ( not a clue about this one).

The reference voltages are right on spot.

I will check the continuity of the input switch and follow the signal input while I wait for a replacement battery.

Roger

[grizewald]

err  some damadge indeed

It didn't look too bad initially...



but when I removed the two yellow electrolytics, it was obvious that the alkali had spread over a wide area. All the vias underneath the battery are open circuit, including the one at the top of the picture which I'm just about to fix with a wire. Then, every via where the solder looks grey will have to be drilled out and given the same treatment.

Most sane people would declare it "beyond economic repair".



Sorry rodd, I'll stop hijacking your thread now.

[rodd]

No problem. All information is usefull.


Enviado do meu iPhone usando Tapatalk