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PSU Ripple

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?

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(probes are on 10x and I did compensate them first)

Reply to
Cursitor Doom
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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

Reply to
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!

Reply to
Cursitor Doom

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

It is AC coupled, yes.

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.

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

Reply to
Cursitor Doom

It's the same shape with DC coupling! I have no idea what the rest of your message means.

On another forum one of the accredited gurus said to do the measurement *unloaded* which I did. Loaded makes more sense to me, though. I'll give it a whirl next time I get an hour to spare (that could be some days away...)

I *can* open the box if I have to. But it's quite a big deal so I just wanted to know there was a fair chance the bridges could be the issue first, that's all.

Reply to
Cursitor Doom

I did have a light bulb moment at about 3am and came to this conclusion. I think of these signals as 'ghost voltages' and they're the same thing that cause electricians to get false positives for mains voltage on cabling that isn't live when they use their hi-z neon screwdrivers. It's the same thing we're just calling different names if I understand you correctly - which I believe I do.

I have a hunch it will just make it all the more obvious there's something amiss with the rectifiers.

Reply to
Cursitor Doom

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