Re: PSU Ripple Update

On Mon, 25 Mar 2024 10:18:07 -0400, legg <legg@nospam.magma.ca> wrote:

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

Indeed. Anyway, if they hadn't made it such a bitch of an area to
inspect, I'd have spotted the issue at the outset.