I never had this problem with an H744 power regulator, but once I had a
horrible intermittent problem in the RK05 power supply where the caps
were 'wafting in the breeze' of the fan.
Metal fatigue had created almost microscopic cracks around the part of
the land where the screws attached, causing a disk fault every week or
so. It was in one of four drives and the only way I found it was to
swap the drives one by one and wait, since the emerg signal was paralleled!
I told the chief engineer that the problem was the same thing that
caused planes to crash, and he suggested maybe the cargo door had fallen
off! (that puts it in 1972 since it was AA Flight 96 that had just
happened!)
Try reheating around the screws.
cheers,
Nigel
Nigel Johnson, MSc., MIEEE, MCSE VE3ID/G4AJQ/VA3MCU
Amateur Radio, the origin of the open-source concept!
Skype: tilbury2591nw.john...@ieee.org
On 2022-01-07 15:21, Rob Jarratt via cctalk wrote:
Weirdly, the whine has disappeared. This is after I put the suspect capacitors
back in. Because I had previously removed them for reforming, I wonder if one
of them was not properly screwed in?
Regards
Rob
-----Original Message-----
From: cctalk<cctalk-boun...@classiccmp.org> On Behalf Of Jay Jaeger via
cctalk
Sent: 07 January 2022 16:02
To:cctalk@classiccmp.org
Subject: Re: Source for replacement caps in H744 regulators
On 1/6/2022 7:03 PM, W2HX via cctalk wrote:
My 2c. I am not familiar with a "whine" but certainly a "hum." Sometimes if
a power supply has seen a lot of heavy load over its lifetime, the heat
generated can begin to do things to the transformer. And once that heat has
done its "thing" to the transformer, it stays that way. And no replacing
external components will change the hum. However, there are some
transformers with bolts and nuts that hold the laminations together.
Sometimes they can be tightened to reduce the hum. I don’t know this PS
specifically and whether it falls into this category or not.
I don’t know if what you are hearing is transformer hum, but if it is, you
may just have to live with it.
73 Eugene W2HX
Subscribe to my Youtube Channel:
https://www.youtube.com/c/w2hx-channel/videos
This does not fall "into this category". This is typically high frequency (in
excess of 10KHz) whine, not 60 cycle, 120 cycle or even
400 cycle "hum".
My experience with many PDP-11 machines going back to the mid 1970s, and
those in my collection, is that this whine from the *switching* power
supplies is very common. For some people, it may be above the frequency
that they can hear. For me it is not (I could also hear burglar alarms in
excess
of 20KHz back in the day, though I doubt I could now, at age 70.)
My *guess* is that it comes from the inductors in the switching circuit, and is
*mechanical*, induced by the switching waveform, which in turn is
dependent upon load. If I had one that was really bad, I'd be tempted to put
on a glove for insulation and hold those to see if the mechanical pressure
made any difference.
JRJ
