Re: PSU Ripple Update

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.