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From: legg <legg@nospam.magma.ca>
Newsgroups: sci.electronics.repair,sci.electronics.design
Subject: Re: PSU Ripple Update
Date: Mon, 25 Mar 2024 10:18:07 -0400
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On Sun, 24 Mar 2024 18:20:58 +0000, Cursitor Doom <cd@notformail.com>
wrote:

>On Mon, 18 Mar 2024 07:19:08 -0400, legg <legg@nospam.magma.ca> wrote:
>
>>On Sun, 17 Mar 2024 17:48:07 +0000, Cursitor Doom <cd@notformail.com>
>>wrote:
<snip>
>>
>>Did you replace the rectifiers, until something (anything) changed?
>>
>>The ripple has changed since your last photo, as have your test
>>conditions. You still don't indicate a 0V reference, so we can't 
>>tell what the % ripple IS. 
>>
>>This waveform shows equal phase peaks at the expected frequency.
>>
>>What is your problem?
>>
>>RL 
>>frequency.
>
>I fell into the same old trap as last time and the time before that
>and the time before that....
>It was nothing to do with the PSU. I eventually tracked it down to a
>coax's shield in the RF section which had come adrift. When
>re-grounded, the ripple on the output completely vanished. Must  have
>been somehow picking it up from the mains transformer despite all the
>screening and compartmentalisation in this device.
>All that time I wasted on the PSU - just because ripple *has* to be a
>PSU problem, doesn't it. Until it isn't, that is.

Good to hear you've tracked down the problem.

Actually measuring the output ripple of a functioning linear 
can be an issue, as you're often expected to measure microvolts 
on a DC level repeatedly - requiring carefull decoupling, probe 
technique and sometimes external amplification, if the spec is 
typically silly.

Suddenly you will become aware of all of the unshielded sources 
of low frequency interference in your work area.

RL