Re: 555 restoration

Richard Knoppow

Did you get the fan or fans going? If not that could be the problem. If so my guess is tired capacitors in the PS.

On 9/3/2019 2:55 PM, Sparky99 wrote:
Hi everyone, I recently purchased a 555 - it arrived in very dusty and grubby, but has cleaned up to be in almost mint condition. Despite very clearly not being powered up for a very, very, long time (both fans were immobile ...) it more or less works in the more general sense of the word - a tribute to the quality and robustness of the engineering !
There is one problem however, which is why I'm posting here. On power up, both the upper and lower beam traces are displayed with good brightness. About 3 minutes later, the upper beam fades and then disappears. Turning up the intensity temporarily brings the trace back for a few seconds, but it then permanently disappears. The lower beam is still fine.
Powering the instrument off/on temporarily brings the upper beam trace back for a few seconds only, which seems to indicate that the problem is temperature related. Does anyone have any ideas where I should be looking of what the problem might be?
All the best
Richard Knoppow

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