Hey Siggi,
Thank you for posting additional comments. I had hard times disassembling the attenuator as I could not figure out where the second screw was hidden in the bottom. When I located it, I retrieved the whole block and carefully cleaned all contacts on the PCB the relays too. I did extract the same elements as in your pictures. Need to be careful as all seem quite brittle. But I managed to make it work as the correct noise was then heard "clic-clac" when changing the settings with now a correct reading with 10:1 probe. I could also read 50 ohms for the input resistance while I was having 1 Meg before. So all seem to work fine now. When I reassembled the whole scope and powered it back with the case, I started noticing jumps on channel 1 displaying the >500 mV sign, indicating that the setting is altered by the VAR knob. It was lightly the case before but and I can now see the display intermittently toggles between 500 mV and >500 mV with the AUTO LVL trigger displayed or not. On channel 2, very stable and no toggling at all. If I run EXER 01, I can clearly see an unstable display while turning the VAR knob in Channel 1 and bringing back to the lock position. So the pot is noisy.
I have tried to leak de-oxyder along the shaft several times, but nothing worked. I looked at the pot and I don't think there is a hole somewhere to inject the cleaning spray? Also, please correct me if I'm wrong, but it seems the VAR lock is just a mechanical position and there is no electrical switch behind right? So the > should disappear when the knob is rotated full CW, just before locking. I am not sure what to do next. I have seen 3-pot assemblies for 9 US so I may want to order one and replace the old one. Unless someone has a trick to real clean these potentiometers or encoders? Thanks a lot!
Cheers,
Christophe
