Re: PSU Ripple

On Sun, 10 Mar 2024 21:36:21 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

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)
 

>
If the bridges were working properly, there should be very little 50-Hz in
the ripple.
>
Looks like a bad diode in one of the bridges causing a lot of fault current
in one half of the secondary, and so messing up the other supply too.
>
Cheers
>
Phil Hobbs

Thanks, Phil. Getting those rectifiers out will take some major
surgery and I just wanted verification that by devoting some
considerable time and effort into getting at them wouldn't be a
complete waste of time. I shall proceed  with the extrication!