Path: ...!news.mixmin.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Cursitor Doom Newsgroups: sci.electronics.design Subject: Re: PSU Ripple Date: Mon, 11 Mar 2024 00:53:31 +0000 Organization: A noiseless patient Spider Lines: 63 Message-ID: <88lsuilqjiv3gcgf1fb39s7p26rf832l42@4ax.com> References: <2hjsui1hrfvg55ri9g80bc7qrj4u9rmjvv@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Injection-Info: dont-email.me; posting-host="842509ddb5b6262d421e7f39189230a8"; logging-data="3420635"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19QtGah49DmJhy42oDUEo/z1HUfJ8RydQs=" User-Agent: ForteAgent/8.00.32.1272 Cancel-Lock: sha1:NI802TxulqmoxBeubrEz+H5YpY4= Bytes: 3501 On Sun, 10 Mar 2024 17:25:29 -0700, John Larkin wrote: >On Sun, 10 Mar 2024 23:19:33 +0000, Cursitor Doom >wrote: > >>On Sun, 10 Mar 2024 14:55:36 -0700, John Larkin >>wrote: >> >>>On Sun, 10 Mar 2024 17:28:13 +0000, Cursitor Doom >>>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. > >So you are seeing capacitively coupled random crud. The diodes aren't >even conducting. The only thing you can be sure of is that all the >diodes aren't shorted. It's the same shape with DC coupling! I have no idea what the rest of your message means. >A resistive load and a dc-coupled scope would show you the classic 100 >Hz rectified waveform if the diodes are all good. Try to poke a >DVM-type probe in there and do that maybe. 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...) > >If you suspect a bad part but can't open the box, what next? 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.