Path: ...!2.eu.feeder.erje.net!feeder.erje.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Cursitor Doom <cd@notformail.com>
Newsgroups: sci.electronics.design
Subject: Re: PSU Ripple
Date: Sun, 10 Mar 2024 23:19:33 +0000
Organization: A noiseless patient Spider
Lines: 45
Message-ID: <bafsui5j15sn8e3nn1mlb3eot48v26lf2h@4ax.com>
References: <jcrruih1b8lg091kt3ec9lplqlvhk97ija@4ax.com> <arasui1re9tko073a20tn5n3pbkhhlpn2v@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="3386827"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1/7DyJ625gfJEiMdPxatCl2vs+rPSSayu0="
User-Agent: ForteAgent/8.00.32.1272
Cancel-Lock: sha1:JKwUI6YYJ7e3cEgFNviH+C3ugyM=
Bytes: 2620

On Sun, 10 Mar 2024 14:55:36 -0700, John Larkin <jl@997PotHill.com>
wrote:

>On Sun, 10 Mar 2024 17:28:13 +0000, 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)
>
>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. 

>Why can't you open the box?

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.

>
>Is that old sig gen worth the hassle?

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