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Failing encoders in a Tek TDS-320 scope
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adam4521:
Agree with the sentiment. I have even older 2245A, modern DSO is really nice but want keep classic one working too. Recently it developed a fault with one of the channel ‘VAR’ pots - there is a detent switch to indicate when it is in the ‘cal’ position but that stopped working, leaving the orange warning light illuminated. Not a big problem at all, just annoying.

This scope well over 30 years old but I was pleased to find a seller offering the individual potentiometers and another selling both front panel boards - the latter a very easy repair option leaving me with spare parts perhaps for ‘next time’. £25 I’m happy to spend, so I would encourage anyone with non-running classic scopes to put them up as spares, to help keep other units running.
Calambres:
Now that you say it, I've got another old scope which I use a lot, an analog Hameg HM203-6. It developed the same failure as yours, the potentiometer for the Variable Gain/Cal in Channel 1 went south. The pot is quite unusual in shape and heavily shielded. Fortunately the guys at Hameg (Germany) are still in business and sent me one original spare for a few bucks. Now it's working like new again.

I love this old junk  8)
EE-digger:
inner traces on a pcb should be pretty well sealed from surface level corrosion, moisture and flux residue.  On the surface watch for traces to a pad that originate under the solder mask.  In bad cases, I've seen these short segments gone from acidic residue and humid season.
snoopy:

--- Quote from: Calambres on June 09, 2022, 09:40:22 am ---
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?


--- End quote ---

I had a similar problem with a TDS784 but not sure that it was caused by internal shorts. The encoders are pretty well sealed but there is a tiny gap to get enough lube into. I used CRC-2-26 and sprayed through the straw nozzle into the gap between the shaft and the body and enough of it got in through the tiny gap to clean and lube the control. No problem since ;)

cheers
wasedadoc:

--- Quote from: snoopy on June 22, 2022, 12:54:52 pm ---I had a similar problem with a TDS784 but not sure that it was caused by internal shorts. The encoders are pretty well sealed but there is a tiny gap to get enough lube into. I used CRC-2-26 and sprayed through the straw nozzle into the gap between the shaft and the body and enough of it got in through the tiny gap to clean and lube the control. No problem since ;)

cheers

--- End quote ---
The OP recently wrote: "My TDS320's front panel died definitely. Now none of the controls or buttons are working at all and all the LEDs are permanently on. " I think that merely spraying into the encoders will not address that.
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