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From: legg <legg@nospam.magma.ca>
Newsgroups: sci.electronics.repair,sci.electronics.design
Subject: Re: PSU Ripple Update
Date: Mon, 18 Mar 2024 07:19:08 -0400
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On Sun, 17 Mar 2024 17:48:07 +0000, Cursitor Doom <cd@notformail.com>
wrote:

>Gentlemen (and others)
>
>I only get a few spare minutes a week to look into this, hence this
>update. Hopefully my latest finding might ring a bell for some of you
>and assist in pinpointing the fault with this (linear) PSU.
>So, I've carried out a few more tests and discovered that there is a
>total absence of ripple on the storage caps when all the downstream
>circuitry has been disconnected. So it's totally fine with no load.
>However, as I re-connect all those downstream circuits, the ripple
>commences and the more connectors I re-attach, the worse it gets. This
>is a screen shot showing over a volt of ripple at only about 66% of
>the full supply voltage applied:
>
>https://disk.yandex.com/i/vgxfpXgNp-F4Yg
>
>Now I did check to see if there was anything downstream which had
>shorted or gone low-resistance which could possibly account for this,
>but found nothing amiss. So the question is:
>What could cause ripple to arise when even very light loads are
>applied to the output of a pretty substantial linear PSU?
>
>BTW, the bridge rectifiers were fine and have been exonerated from any
>culpability in this fault.

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.