Re: Any advice on 547 power supply repair?


Robert Simpson
 

Wouldn't there still be a problem if the internal windings have already shorted?
Bob

--- In TekScopes@yahoogroups.com, "Bene's Mails" <bene.dienst@...> wrote:

The solution comes from my dad, he’s an electro-engine builder (excuse me if the translation is bad but I don’t really know whats the name of “Elektro-Maschinenbauer� in english). He said too, that it ist a problem of material degeneration, exactly that the epoxy becomes brittle with the time (a problem that a lot of transformers had in earlier days, he said). So it get microfissures, because of AC caused vibrations, where the moisture becomes encased. The water decreases the insulation ratio of the impregnition and so the leakage current increase. This current heats up the transformer and cause flux degeneration in the ferrite core, so the transformers efectivity decrease and the secondary Voltage fell off. Heating the transformer for a long time under dry enviromental contitions, dehumidifys the epoxy, so he said. The new epoxy seals the old bad epoxy against the air humidity, so it can’t absorb new moisture.

This is how my father described the problem to me. For my part I can say that it has worked well.

greetings an a nice weekend
ben


From: Chuck Harris
Sent: Friday, April 12, 2013 12:07 AM
To: TekScopes@yahoogroups.com
Subject: Re: [TekScopes] Any advice on 547 power supply repair?


I cannot imagine that any solution that involves putting epoxy
on a bad 547 HV transformer will work... heating it or whatever.
I spent several years researching the issue, and found that the
failure is a progressive and irreversible degradation of the
epoxy material.

In my experience, the epoxy has changed from its original composition
to something that is lossy in general, and will absorb water to
become even more lossy.

The only solution I have found to the transformer problem which
lasts long term is to remove the winding, and replace it with new.

I have been selling replacements for the 547 EHT for some years
now.

-Chuck Harris

Bene's Mails wrote:
Cool! I hope the rest of the instrument works fine. Pay attention on the
HV-Supply, I don’t know if you already hear it, but the transformers impregnation
is infamos for absorbing moisture, so that the insulation breaks down and with it,
the HV. Sympthoms for this are a fuzzy trace and inoperative Focus, Astigmatism
and Intensity controls after a period of ca. 20 minutes. A solution which works in
most cases is to dismount the Transformer out of the HV compartment and put it
into the oven at 70-80°C (160-180°F) not higher and leave it for around five hours
in it. Then you mix some epoxy-compound glue and put it on the windings and the
insulation tape. Be careful with the glue, it becomes liquid by heating it up, the
best way is to put it on the upper windings, wait until it’s dry (time for
diffrent temperatures is printed on the pacage), then turn it and glue the other
side. Next, lay it on the side, and glue the first half of the tape, wait again
and then glue the other side. Wehn you finished it, the problem shoud never appear
again.

ben


From: Dave Sent: Wednesday, April 10, 2013 6:30 PM To: mailto:TekScopes%40yahoogroups.com
Cc: Bene's Mails ; mailto:davidwhess%40gmail.com ; mailto:stefan_trethan%40gmx.at Subject: Re:
[TekScopes] Any advice on 547 power supply repair?


I replaced the 6BY8 in the 100V power supply and that fixed the problem. Thanks to
all who responded ...

Dave



On 3/29/2013 11:18 AM, Bene's Mails wrote:

good luck! Write here again, when you’ve fixed it!

ben

From: Dave Sent: Friday, March 29, 2013 2:58 PM To: mailto:TekScopes%40yahoogroups.com
Subject: Re: [TekScopes] Any advice on 547 power supply repair?


OK, I understand now. Thanks very much, Ben. Now, it's time to work on that
'scope...

Dave


On 3/29/2013 9:22 AM, Bene's Mails wrote:

Yes, but all other circuits where the +100V are used. I know it’s a lot of work,
but when the supply is allright, then you must find the problem in the rest of the
instrument.

ben






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