Re: PSU Ripple

On Sun, 10 Mar 2024 14:55:36 -0700, John Larkin <jl@997PotHill.com>
wrote:

On Sun, 10 Mar 2024 17:28:13 +0000, Cursitor Doom <cd@notformail.com>
wrote:
>

Returning to this Marconi signal generator which has a lot of ripple
on the (linear) PSU output, I managed to get probes through a barely
accessible crevice and get a couple of screen shots of the rectifier
outputs I'm seeing on the scope.
So there's mains incoming which goes into a toroidal transformer and
thence to the rectifiers. There are two secondary windings on the
transformer and they each get their own bridge rectifier. This is the
waveform that's being applied to the storage caps of the PSU (which
I've disonnected for testing purposes).
The outputs of neither rectifier look at all correct to me. What does
the Panel make of them?
>
>
https://disk.yandex.com/i/CP8qRMy-QA-fCg
https://disk.yandex.com/i/ubNazf1pFhuNtg
>
(probes are on 10x and I did compensate them first)

>
Are the filter caps removed? Is there a load on the rectified DC?

There isn't a load other than the probe itself. The downstream storage
caps are completely disconnected.

I assume the scope is AC coupled. You may be seeing a lot of
capacitative coupled hi impedance cruft, not necessarily a failure.

It is AC coupled, yes.

Why can't you open the box?

It *could* be done, but the manufactures have made it as difficult as
possible. I suppose I should just be grateful they haven't potted
everything as well.

>
Is that old sig gen worth the hassle?

Yes. It's a 10khz to 5.4ghz and they still fetch a tidy sum despite
being 25 years old.