12 Jan
2002
12 Jan
'02
10:57 a.m.
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
12 Jan
12 Jan
6:14 a.m.
Date: Sun, 13 Jan 2002 00:57:51 GMT
From: pete(a)dunnington.u-net.com (Pete Turnbull)
To: Discussion re-collecting of classic computers
<classiccmp(a)classiccmp.org>
Subject: H744 regulator whistle
Reply-to: classiccmp(a)classiccmp.org
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.
Pete,
Sounds like PSU is reacting to overloading or medium shorts
downstream of that PSU outputs. Also can happen with dried
up capacitors (too high ESR).
I remember that too well when I shorted out a switching VCR's PSU
thanks to bent pin. :-) Rising thin WHISTLE then *snap!* with mini
fireworks (chopper transistor blowing up) then silence.
Blown bits tally: one of resistor series, chopper, chopper
transistor driver, fuse, straightened out pin. VCR functioned
afterwards for years. Even that friend's vcr is funai, with my mods
to improve it's quality, that thing lasted longer than it should be.
(!?) :-)
Cheers,
Wizard
11:54 a.m.
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
------------------------------------------------------
http://xgistor.ath.cx
------------------------------------------------------
----- Original Message -----
From: Pete Turnbull <pete(a)dunnington.u-net.com>
To: Discussion re-collecting of classic computers <classiccmp(a)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
13 Jan
13 Jan
6:27 a.m.
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ard＠p850ug1.demon.co.uk -
jpero＠sympatico.ca -
pete＠dunnington.u-net.com -
sipke＠wxs.nl