Re: 7A26 edge distortion


 

On Wed, Oct 21, 2020 at 06:55 AM, John Gord wrote:


The 7A26 has a number of small ceramic trim caps of a design that has proved
to be prone to going open circuit. You may have failures at the same point of
both channels, unlikely as that seems. I would suspect C1432 and C2432 in
particular, since they seem likely to affect the highest frequency signals.
Try turning them: if they have gone open circuit turning them will have little
to no effect. If those are not the problem, try others!
Hi John,
I know the problem with the trimmer caps. I found several that had no effect, initially blaming that on the lack of HF content in the signal as it appears and not expecting a multi-device failure.
I temporarily put some small caps (3 - 10 pF) in parallel with one trimmer-cap at a time and so far, I've found 5 (yes, five) that immediately made the pulse steeper, without overdoing it, in both channels!
I'm afraid this is going to exhaust my donor supply...

Raymond

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