Repairing a Sanwa PS-8 Pocket Multimeter - Now Fixed!

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Hi all,

I know everyone here is a bit of a test equipment nerd , so I thought I'd write up a post as I tried to repair this lovely pocket multimeter! It was bought quite a few years ago and I re-discovered it the other week... lo and behold, it doesn't quite work...

Voltage... fail!



Continuity... fail!



Resistance... fail! (Ignore the LCD screen, it is working fine, but camera caught it in the middle of changing digits)

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Let's open it up!

Wheel
Two screws and we're in (like Flynn ). Nice selector wheel with copper (?) contacts - better keep my fingers away!



Back
Looks like there's going to be a lot of surface mount goodness in here (surprising for the vintage...)



Front
Well this is annoying... to release the PCB we need to delicately desolder a few wires - I wonder how they manufactured these en masse.



But nothing a soldering iron can't help



Look at all that corrosion from leaky batteries! Better clean that up as a first effort, hopefully we didn't permanently destroy anything. Also look at all that MELF goodness. (Dave would be all over this )

This isn't a review, but there looks to be absolutely no input protection? (Expected for the vintage I guess...)

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No improvement after cleaning the corrosion off the board

Problem found?

Checked the resistance from probe tip to it's PCB solder joint: black seems okay, red is in the megaohms. Could this be it? Replace the red lead with some other wire lying around...



Put the necessary bits back together, and... bingo! Got you.



Replacing the probes

Note to self... check whether the tips are screwed in before freeing them with a soldering iron. (You can see the heat damage on the red probe below haha)



I thought it would've been the solder joint coming loose between the wire and tip, but surprisingly, it appears that it's the wires themselves.



The red wire appears as if it's (literally) hanging on by a thread. The black at 6 ohms isn't fairing much better to be honest... best to replace them both. A bit tricky to find the right gauge of wire to fit through the probe body, but our donor today is cable from a set of old crappy PC speakers!



Alright, everything cut to length and soldered back together (mostly).



Everything fits back into the box nicely and yay it works!



(Side note: the continuity buzzer on this thing is amazing - absolutely instant with latched tone!)

Finally!

A beautiful little pocket multimeter, 100% working and now with white probe leads! (I'm actually quite liking the white, it's growing on me)