Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Cursitor Doom <cd@notformail.com>
Newsgroups: sci.electronics.repair,sci.electronics.design
Subject: PSU Ripple Update
Date: Sun, 17 Mar 2024 17:48:07 +0000
Organization: A noiseless patient Spider
Lines: 23
Message-ID: <3haevi1jbhf4poc4s32t99391bq4tqfc42@4ax.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Injection-Info: dont-email.me; posting-host="6b68b13d0f8cd75cb4b90b640cffe83e";
	logging-data="3838905"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1/CRPx+7HwvCfjmRI9tfQ0gqtBKwjB7TtI="
User-Agent: ForteAgent/8.00.32.1272
Cancel-Lock: sha1:O0DV/z3195ZE/ZW/aBHRG/GX7MU=
Bytes: 1969

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.