Metrahit 18S

[najrao]

Picked up this 'Rishabh' 18S in clean condition, for a low price.

Though unmolested, it does not work for 'diode', capacity and ohms. For diode, I get a continuous beep and zero reading even with probes unplugged. The ohms fails to auto zero with probes shorted, and displays a wandering hundreds to megohms.

Two diodes, apparently back to back, are SHORTED. See them just under the daughter board on the left.

Yes, I have read through the multiple threads on Gossen Metrawatt in our forum.

The manufacturer has not done a good job of soldering, and has not cleaned the board at all after, it seems. I want to do this too.

Request help to locate the fault and save this excellent instrument. Thanks.

I have read through the multiple posts in this forum.

Edit: The two diodes are NOT shorted. There is a R50 across them.I did remove them to check, unnecessarily.

[shakalnokturn]

It looks as if someone has had a try at fixing it before, there has been solder rework on the resistors around the switch.
If it looks dirty take it apart and scrub it all clean, when repairing handheld DMM's delaying this step has often proven to be a waste of time.
Also consider that the switch may have been previously disassembled and not realigned correctly.
Have you been able to confirm with a known good meter that V and A are giving correct readings?
If you do disassemble for cleaning make the most of it to take better photos, you'll have more chance of getting help.

[najrao]

Thanks, Shakalnokturn.
I have solved it ! :  Small compression spring hidden inside the red switch contact carrier was simply absent! It is essential,  to hold the contact pressed lightly against the switch tracks. It's absence was inferred by beeper test.
Snapping open the contact carrier was awkward to say the least. I managed to find a spring to fit, and bingo!
Unfortunately my new spring is bit harder to compress, which lifts the carrier arm an extra 0.5mm, and presses a little harder on the tracks. Finding an exact spring is a wild chase, and I would rather not try disassembing the all-plastic carrier again.
The back of the board has a large plastic shroud which also carries the display and backlight. To gain access to the back of the switch, this shroud has to come off, but won't,  without desoldering at least four awkwardly located pins at the back of the lcd.
This makes cleaning impossible. Dunking the whole board in IPA is a way, but what about the pots and trimmers?
I checked DCV calibration against an U1242 calibrated by Keysight. Very good! All other functions seem to work as intended.
I need a user manual, Rishabh's support is useless. No download available anywhere.
Thank you again for help.
Edit: I got the exact spring from another  Rishabh mule, perfect. R support sent me a scanned user manual, nice.