H744 regulator whistle

From: Sipke de Wal <sipke_at_wxs.nl>
Date: Sat Jan 12 19:54:24 2002

Sometimes it helps to fasten coils a bit with siliconekit
or araldite, or if a bit of heat is not a problem thermal-glue
Silicone kit has the added benefit of dampening high freq.
vibrations cause it has a somewhat rubbery constitution....

Do not totally immerse the coil in glue cause you might run
into thermal problems, just enough to fixate it a bit (better).

It worked for me in TV-sets with a similar problem

Sipke de Wal

----- Original Message -----
From: Pete Turnbull <pete_at_dunnington.u-net.com>
To: Discussion re-collecting of classic computers <classiccmp_at_classiccmp.org>
Sent: Sunday, January 13, 2002 1:57 AM
Subject: H744 regulator whistle

> I have two H744 regulators in my PDP-11/40, along with an H7441, H745, and
> H754. I also have two spare H744s and one each H745 and H754. All the
> H744s emit a fairly loud whistle, and it's driving me nuts. I've seen a
> note somewhere that a loud whistle is caused by the coil de-laminating, but
> I don't think that's the case. I tried swapping the two original H744s for
> spares, no difference. I also tried swapping the coil from the spare H745,
> which runs almost silently, and that made no difference either. I don't
> think I can just remove (short out) the coil either, as this is a switching
> regulator and the coil is needed to make it work properly.
> Any suggestions?
> --
> Pete Peter Turnbull
> Network Manager
> University of York
Received on Sat Jan 12 2002 - 19:54:24 GMT

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