Amplifone HV problems

Hi everyone.

A few months back, I wrote about the 19" Amp in my Quantum being very very dim,
and very out of focus. (it was previousely working just great). Since then, I
haven't had much time to work on it due to travelling a lot for work. Last
night, I decided to get back to it. Let me document as many details as I can:

When I picked up my Quantum, it was playing blind. It had the red HV
transormer, so I figured that was the problem. I planned to install a Wintron
and cap the board, but in the meantime I decided to borrow the HV unit out of
my Star Wars upright so I could play some Quantum. It worked fine.

The Star Wars HV board is a blue board that has been modified with the diodes,
50ohm 5 watt resistors, and a Wintron. It appears to have also been recapped
recently.

The setup was fine for some time, and I put off installing the Wintron in the
other HV board until I could really spend the proper time researching how to do
it properly. I had swapped the board back and forth between the SW and Quantum
a few times as I was troubleshooting some SW boardsets.

The last time I put the HV in the Quantum, I had the dim/unfocused problem.
Tried it in the SW as well, same problem. The 50 watt resistors would get
*very* hot, to the point of smoking. I also measured the HV at the tube and I
had around 8kV. Last night I finally sat down with the Amplifone FAQ Guide,
and started poking around.

Both 50 watt resistors were open. I replaced those. The added diodes checked
out fine with the diode function on my meter. Also, the BU406D also checked
fine with the meter. I checked the output of the deflection board, it appeard
to be within spec. I checked the output of the regulators, that seemed to be
okay. With new resistors in there, I decided to plug it all in and try it. I
still had the same type of problem. I could smell the resistors getting hot,
had little or no picture, and the HV was still around 8kV.

One other item to note- Q4 on the HV board was not present. This seems very
strange to me- I have never removed any components from this board (until last
night), but the board was up and running for quite some time. Apparently Q4 is
not important?

Any help is greatly appreciated.
Thanks
Robb Gonyer
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Received on Fri Aug 20 14:13:45 2004