Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Cursitor Doom Newsgroups: sci.electronics.repair,sci.electronics.design Subject: Re: PSU Ripple Update Date: Sun, 17 Mar 2024 20:15:31 +0000 Organization: A noiseless patient Spider Lines: 31 Message-ID: References: <3haevi1jbhf4poc4s32t99391bq4tqfc42@4ax.com> <65f74d1b$0$876048$882e4bbb@reader.netnews.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Injection-Info: dont-email.me; posting-host="6b68b13d0f8cd75cb4b90b640cffe83e"; logging-data="3905904"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+OwP6Fo8pmxcDzeLW+cA8UCB714gomw9c=" User-Agent: ForteAgent/8.00.32.1272 Cancel-Lock: sha1:TPcyQsRvSn/+9E9gnhkW9OexKj4= Bytes: 2517 On Sun, 17 Mar 2024 16:05:46 -0400, bitrex wrote: >On 3/17/2024 1:48 PM, Cursitor Doom wrote: >> Gentlemen (and others) >> >> I only get a few spare minutes a week to look into this, hence this >> update. Hopefully my latest finding might ring a bell for some of you >> and assist in pinpointing the fault with this (linear) PSU. >> So, I've carried out a few more tests and discovered that there is a >> total absence of ripple on the storage caps when all the downstream >> circuitry has been disconnected. So it's totally fine with no load. >> However, as I re-connect all those downstream circuits, the ripple >> commences and the more connectors I re-attach, the worse it gets. This >> is a screen shot showing over a volt of ripple at only about 66% of >> the full supply voltage applied: >> >> https://disk.yandex.com/i/vgxfpXgNp-F4Yg >> >> Now I did check to see if there was anything downstream which had >> shorted or gone low-resistance which could possibly account for this, >> but found nothing amiss. So the question is: >> What could cause ripple to arise when even very light loads are >> applied to the output of a pretty substantial linear PSU? > >You sure you got your probe division/scope division configured congruently? Yes, it's on 1x @ 5ms. The only thing I can think of is some sort of issue with a rogue feedback signal which has ripple on it and is causing the PSU to (mis) regulate accordingly. But I have no schematic and there's none available online either, so I can't check for that.