Re: WG 19v2000 flyback sub?

Yes, I have spoken of this test a year or two ago as well. The ideal is to
run the audio signal generator at the frequency of the transformer and then
watch the voltage output. The ampliphones run around 19khz and if the
input voltage is 1/10 of the normal input, then the output voltages should
ALSO be 1/10 or normal. Easy test if you have access to an audio gen. Or
you can hook the hv transformer to the output of the 555, just watch that
the normal B+ is isolated from the input winding. You want to have the HV
transformer with one input to the 555 and the other to ground. If the 555
is running on 12VDC, then you are about 1/5 of normal working voltage in...

John :-#)#

At 04:29 PM 12/4/00, Marc Alexander wrote:

>I had some luck testing the infamous dead red Amplifone HV transformers
>by using an audio frequency generator connected to the B+ winding,
>and looking at the other windings output on a CRO.
>I don't have my notes here but I think I put in 10KHz, 10Vp-p sine wave
>from an ordinary signal generator,
>and looked at the outputs, if you want to know more send me a message,
>I'll dig out my notes with the voltages and waveforms I saw.
>The red transformer has an integral diode so I couldn't do resistance
>measurements on the output. (note this is an Amplifone one)
>Kind of a manual version of the LOPT meter I guess
>
>Marc
>
>
> > Even if the HV secondary winding was open you should still get the lower
> > voltages. Thus even if you get an infinite resistance on the HV lead you
> > should still get the lower voltages as they are, AIR separate windings.
> > Thus if NO output voltage at all, and the primary winding seems good, then
> > I would be looking at the driver circuitry...one of Bob Parker's (Dick
> > Smith Electronics in Australia) flyback/LOPT meters would be handy about
> > now (not an ad exactly, but we as well as a few other folks sell them).
> > Very handy to verify flybacks/HV Xformers.
> >
> > John :-#)#
> >
> > At 06:48 AM 12/4/00, Robert Bayes wrote:
> >
> >
> >
> > > >If you get oscillation, but nothing out of the flyback (actually a HV
> > > >transformer, as a flyback needs a yoke winding for it's operation-but
> > > >that's another group (Rasterlist))) then I would take a close look
> at the
> > > >driver transistor first, and it's connector.
> > >
> > >Thanks, John, I have checked it to the extent my test equipment will allow
> > >(DVM, scope).
> > >
> > > >
> > > >On the other hand, I have had those HV transformers that had loose
> winding
> > > >assembly and the wires leading from the coil break at the solder
> terminals.
> > > >You might be able to re-solder them if you bend the broken one out
> > > >carefully, burn off the insulation, then add a tiny extension wire. I've
> > > >managed to fix a couple that way. Oh, and then wedge in silicon glue to
> > > >freeze the coil windings. Other folks might want to check this on
> their B&W
> > > >vector HV transformers to make sure theirs aren't loose and do some
> > > >preventative maintenance.
> > >
> > >
> > >
> > >I removed the flyback and inspected it for broken connections as you've
> > >indicated. All connections were sound. However, I still have a problem
> > >determining the continuity of the HV secondary winding. I read
> > >"Sci.Electronics.Repair FAQ Testing of Flyback (LOPT) Transformers" on the
> > >web and it was ambiguous about measuring the flyback coil continuity.
> > >
> > >If I cannot read a finite resistance (before the HV rectifier) and *any*
> > >identifiable terminal on the flyback itself, I have a broken flyback -
> > >right? Unless I'm missing something here, or took the wrong exit to the
> > >Magic Kingdom, the HV secondary is open. Please correct me if I'm wrong.
> > >
> > >Where the anode wire physically connects to the core there is a small
> amount
> > >of movement. Could this wire have worked itself loose? If so, what
> is the
> > >likelihood of success in removing that epoxy, RTV or whatever it is
> coating
> > >the transformer and resecuring the connection?
> > >
> > >I really appreciate your help.
> > >
> > >
> > >
> > >Robert
> > >
> > >
> > > >
> > > >John :-#)#
> > > >
> > > >At 08:33 PM 12/2/00, Robert Bayes wrote:
> > > >>Thanks, John, for your quick response.
> > > >>
> > > >>
> > > >>
> > > >> >Are you sure the transformer is open?
> > > >>
> > > >>As best I can tell. HV circuits are not my strong suit. I measure
> approx.
> > > >>10Mohms (depending on the humidity down here in Houston) with the
> HV diode
> > > >>*out* of circuit. Should I see this *high* a reading?
> > > >>
> > > >>
> > > >>A common failure on these is a bad HV
> > > >> >diode...
> > > >>
> > > >>I bought one of those just in case.
> > > >>
> > > >>do you get the screen voltage (400V) and the 90V output from the HV
> > > >> >unit?
> > > >>
> > > >>I get *no* screen voltage (~0.0V), *no* focus voltage (~0.0V) and only
> > >about
> > > >>10V (should be ~95V) for the spot killer circuitry. I am mindful
> of the
> > > >>characteristic hi-z of the circuit but it shouldn't yield *that*
> much of
> > >an
> > > >>error through my DVM! Please correct me if I'm wrong.
> > > >>
> > > >>The HO circuit _is_ oscillating though. The feedback must be coupling
> > > >>through the transformer core.
> > > >>
> > > >>If so, then the unit is almost running...likely a bad diode at that
> > > >> >point...there has been discussion here about sources for those
> > >diodes...I
> > > >> >use ones from old B&W TV's...
> > > >> >
> > > >>
> > > >>
> > > >>Lord knows, I hope you're right. However, so far, it seems to point to
> > >the
> > > >>flyback.
> > > >>
> > > >>What do you think, given this *new* information? Any suggestions?
> > > >>
> > > >>Sincerely,
> > > >>
> > > >>Robert
> > > >>
> > > >>--------------------------------------------------------------------
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Received on Mon Dec 4 01:29:10 2000