29 Aug
2010
29 Aug
'10
6:38 p.m.
Tony Duell wrote:
As some of us know all too well, flyback transofrmers
fail, and are often
next-to-impossible to get. So I have been wondering if it's possible to
make a replacement...
There would appear to be 2 parts to this.
1) Desigining the replacement. I think we can assume a schematic of hte
horizontal output stage it's going to be used in. But how do you
calcualtor the number of turns on each winding? Since the origianl is
likely ot be potted in epoxy (for HV insulation reasons), counting the
turns there is impossible.
Are there any good references (books, web pages, etc) on the desing of
such transoformes and/or the design of horizotnal output stages? I would
have thought something must exist, but I've never seen it.
2) Making the replacement. It owuld ahve to be vacuum pmpregnated, I
think. But I believe some model engineers who make internal combustion
engines make the own ignition coils (and vacuum-impregnate them?). Again,
any good references on doing this?
-tony
Oddly enough, vintage TVs using pictures tubes of the same size as the
monitors you are trying to repair often have flybacks that could be used
with a bit of tinkering. You need only a few voltages out, and if you
know if the original monitor was tube or solid state then you know
somewhat what vintage TVs to hunt for (thrift stores/flea markets). You
also need to find one that has similar horizontal and vertical yoke
resistances to your monitor, as well as the B+. If you find these then
flybacks are somewhat interchangable with some mucking around to get the
pinout to match your monitor requirements. Due to the frequency these
are running at a CGA monitor yoke I would expect that the impedance
should be similar to the impedance of a similar sized TV yoke with
similar resistance windings to your monitor.
Schematics of your monitor and the TV you are swiping the flyback from
would be a big help...
Flybacks design is available (perhaps at a cost) from places like:
http://www.innovatia.com/Design_Center/mag_desn.htm
Which I found that as an early choice using the following search term
"flyback transformer theory" in google. A bit further down there are a
few PDFs on desinging Flybacks.
You can test flybacks using Bob Parker's Blue Ring Tester (sold at a few
places - like my shop) or you can make your own ring tester using a
scope and an audio signal generator - simply pump into the flyback a
couple of volts at the flyback frequency and see what comes out of the
lower voltage windings...should look fairly clean if the flyback is OK.
I have some older B&W flybacks for Motorola B&W monitors as used in
video games in the 1970s as well. These tend to be open frame flybacks.
John :-#)#
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