Re: Magnavox FP5230 repair

Wow, this is some good stuff.  Thanks!

Bill S. wrote:
If you get sound, the "regulator" is probably fine. 

I'm assuming they were talking about the flyback transformer.

More likely the large signal board (LSB), which has the power
and deflection circuits.


Is that the large board dead-center in the rear the TV?

Having said that:
If the tube filaments light, you have horizontal deflection.
The buzzing you hear is probably vertical deflection.


I don't see any activity in the tubes.  Is it very subtle?

A bad thing happened on some of these sets if connected to, say, a
VCR that goes to blue screen due to loss of signal.  Blue tube after
being driven 100% for awhile gets so hot that it will actually crack
and lose vacuum.  Sometimes you can see the crack through the lens,
sometimes it drips onto the LSB, which burns things up, but in either
case the blue tube now draws excessive beam current which shuts down
high voltage.  Usually throw away when this happens.

I'm assuming I'd be able to tell this right away. I don't see anything amongst all the dust in there television.

If that hasn't happened, a common electrical failure is for the high
voltage transformer T900 to break down, which causes the HVOT transistor
Q906 to overheat and short out, which blows open 0.33 Ohm fusible
resistor R934.  R934 is hidden in front of the heat sink on the right
front of the board.  It's not easy to get at, but easy to test once you
do.  If open, it usually means T900 and Q906 are both bad.  Couple hun
to fix, but usually worth it.

That's some good tips. I got my gloves on and started playing around with that resistor. It was exactly where you said. My multimeter isn't the best, so I don't know if it would detect that as a short. It certainly didn't. I know I wouldn't get the specified resistance if I tried plugging in straight, but I figured the equivalent power-off resistance (assuming a day unplugged) showed 60k kOhms for that resistor. What is most telling is it looks like a chunk on the right side of it has burnt out. It's rough right there, so I suspect it has blown.

If that's a sign that it's blown, I'll clip it off at one end so I can measure current through that path. Do you know how much current should go through that when powered up? I just wanted to check before I did that. I don't have a soldering iron on hand right now. But if it comes down to that, I can get a Weller in a hurry.
.

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