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Failing encoders in a Tek TDS-320 scope
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Calambres:
Hi there!

My Tek TDS-320 scope recently developed a courious syndrome: all four encoders (Vert. and Hor. position, Trigger level and multifunction encoder) behave randomly and "jumpily". The other two rotary knobs (VOLTS/DIV & SEC/DIV) work perfectly but they're not encoders but rotary switches.

I extracted the panel, cleaned all encoders with generous amounts of IPA as well as the connectors for both flat cables to no avail. They still work randomly. To my surprise, when the scope is on for some time, all encoders begin to work OK again  :o

I've seen this youtube from a guy that's having the same issue with just one encoder (the multifunction knob) and how he found that there was some internal short and how to "zap" it out:



I'm refraining from going that way because it does not seem to me coherent with everything working OK again once my scope is running for a while and hot. Don't see how the operating temperature can make such an internal short to disappear in all four encoders at once  ::)

Don't know what is really happening here... Any ideas?

This is one of the offending encoders (img. taken from the aforementined youtube)
Code: ESZ0D-S00-ES0002   311-2534-00-0103X

wasedadoc:
What do those four encoders have in common? Eg All ground and voltage fed by same PCB tracks, all are handled by the same processor?
Calambres:
Yes, I guess so...
nctnico:
I'd check for leaky capacitors first. Maybe the electrolyte has eaten away a via or caused a short.
Calambres:
I forgot to tell that I replaced the couple of SMT 30uF 10V lytics in the encoders board. One of them was leaking and damaged one pad but I managed to arrange it. Once desoldered the leaked one measured below 100nF. The other SMT lytic in that board was 20uF and no trace of leaks but changed it too just in case...
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