I had the exact same problem with the digits on my Keithley 191. It was a cracked solder joint on the transformer, which is soldered directly to the PCB, which can explain why it cracked in the first place. Try that first.
I'd also clean that flux off and take it to a cal lab if budget allows. Screw that, I would resolder the parts completely. Someone messed with the low leakage circuitry. Let's hope they didn't mess with binned parts or matched pairs or anything like that. ***Is that metal can the voltage reference???!!!*** Go download the schematic off keythley.com while you can. You will have to leave your email address but it's okay, they don't spam. Try to figure out what was botched/repaired.
I got the schematic off the internet when I bought it, so I'd have it ready. If you go by the solder flux residue, it looks like what was replaced was a small bridge rectifier, a low power 15V regulator, and some signal conditioning components in the attenuator section.
P.S. if you're going to restore the plastics, do tell us. I'm interested.
Will do. I will have to re-attach plastic parts and repair others, and general clean-up.
Good luck. That 4 wire resistor/relay(beside the switches, furthest from viewer ) doesn't look very good.
It doesn't look good but that's just the way it's made. I thought the same thing but it just has a case that looks bad, it has not been damaged.
I have one winging it's way across the Atlantic to me. Saving 5l of pure methanol for cleaning the board in places ( not the switches) and then will see how it behaves. Has the battery removed by now, to cut the shipping mass.
Yea mine needed cleaning too. I need to get some methanol.
Looks like a bit of a challenge, good hunting!
Thanks for sharing your work.
Thanks, I'll post more today as I investigate things.
In the meantime I need to repair the front panel, because the overlay has been mucked up by being re-assembled improperly. Some of the edges are curled up pretty badly. What I'm doing now is not gluing it but trying to impart a flat "memory" to the mucked up plastic overlay. I want the plastic to lay flat by itself before I glue it down, so it won't try yo pull off later.