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, 24 Mar 2024 18:20:58 +0000 Organization: A noiseless patient Spider Lines: 51 Message-ID: References: <3haevi1jbhf4poc4s32t99391bq4tqfc42@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Injection-Info: dont-email.me; posting-host="c08a9455afafb065202a3accf161b866"; logging-data="552756"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/yuHvmzkLK+dPcvA1GkWCSCsdlt5OQWHQ=" User-Agent: ForteAgent/8.00.32.1272 Cancel-Lock: sha1:PV3UmW2CJK8azccfCFlyWrVsqjQ= Bytes: 3186 On Mon, 18 Mar 2024 07:19:08 -0400, legg wrote: >On Sun, 17 Mar 2024 17:48:07 +0000, 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? >> >>BTW, the bridge rectifiers were fine and have been exonerated from any >>culpability in this fault. > >Did you replace the rectifiers, until something (anything) changed? > >The ripple has changed since your last photo, as have your test >conditions. You still don't indicate a 0V reference, so we can't >tell what the % ripple IS. > >This waveform shows equal phase peaks at the expected frequency. > >What is your problem? > >RL >frequency. I fell into the same old trap as last time and the time before that and the time before that.... It was nothing to do with the PSU. I eventually tracked it down to a coax's shield in the RF section which had come adrift. When re-grounded, the ripple on the output completely vanished. Must have been somehow picking it up from the mains transformer despite all the screening and compartmentalisation in this device. All that time I wasted on the PSU - just because ripple *has* to be a PSU problem, doesn't it. Until it isn't, that is.