Re: 465B strange ripple


On Wed, Feb 24, 2021 at 02:58 AM, Siggi wrote:


Hey Stephen,

I haven't read this thread in detail, so please forgive me if I'm giving
you redundant advice.
No problem.

First, here's a document you should probably read if you haven't already:
I will read that. Thank you.

Given the equipment at hand, you ought to be able to isolate the origin of
the noise. First is to figure out its frequency, if it's your line
frequency or double your line frequency, that'd hint at power supply
primary filter caps or bad grounding.
Ok... I haven’t seen anything that is supposed to be grounded and isn’t... but maybe..
I’ve already changed the 100v and the -8V filter caps. And the ones I replaced did test good.
I have no ripple on the other rails either, but I will also change the 55V cap as well...

Since the noise is stationary with
the line trigger, it's a fair bet that it's your line frequency bleeding in
I guess, yes...

If you look at the block diagram on page 10 of the document I linked,
you'll maybe be able to isolate this a little further. By using the XY
mode, you can e.g. see whether the noise is present on the Y. If you can
trigger on it, that isolates it further (though it looks like a very low
amplitude signal, so might be hard).
I forgot to mention that while in XY mode, I NEVER get a clean dot. It’s always a very small line about 3 mm wide.

By checking the signal on your CH1 output on the back of the scope, you'd
be able to see whether it's originating from the attenuators/vertical
Hmmmm.... I think I did that...

BTW: Do you know for sure that the outlet the scope is plugged into has a
good ground?
Well... none of my 9 other scopes do that. Although I may have noticed that on my 466 as well...
I’ll have to recheck.

Thank you.

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