Question about Philips Magnavox 51MP392H Rear Projection Television
For a past couple of nights recently, the picture would start to "Shake", I guess is a good description. then once or twice, the picture would sort of
"Wink" out, but then reapear w/ no further issues. Then on occasion
would shut down after this. After letting it set for a couple mins,
turn it on and it would be ok the rest of the night. I thought maybe
loose/cold solder joint some where, because it seemed to come back
after tapping wiggling board sometimes, but what do I know.
Well I had it on this morning for a bit, worked ok, had to go do some
things in town, and shut it off. Come back today and all it will do
now is power up for about 3 seconds, then shut down w/ a real faint
sort of instantaneous "Squeak" sound (luv my descriptions so far???...lol)
This is all it will do now. I got the HV/Vert def board out on bench
lookin @ it now, but not even sure if its on this one or other board.
Was hoping theres a small case history of this issue or if anybody has
an idea on what to check 1st. horizantol output (D2539) seems ok (Q802)
but then again i ask...what do I know.
Well after replacing that diode anyways, i connected back up, now tv
will power on, but no HV, 15watt 30 ohm resistor (R938) near FBT, cold
as a stone, theres another on other side of FBT (R980) that gets
warm/hot. Had a retired TV guy over here last night, but he was a
bull...burnt up a trace/pad tryin to remove a diff diode that was good
anyway's, bitchin/moanin bout not havin service manual,etc..then he
broke the tip of my 100w gun. Hence why I rather do these things myself.
I repaired the damage and put it back together to see what the state of
the union was. Like I said, set powers on now, have audio, but no
HV...vertical looks to be there...I'm afraid I'm lost unless anyone
there has a schematic for this Mag/phil
(That is if anybody is reading this babble)
If the video is shrinking and expanding then its likely the opto chip is doa. Its a common problem on the older sets. Check with www.magnavoxhelp.com and see if they have a chip kit for your model.
Posted on Sep 13, 2008
Jeez, you ramble on as bad as I do (must be another old fart).
It sounds like you know enough to be dangerous.
Getting service literature is not likely, BTW, Sam's Photofacts is not keeping pace with the proliferation of models, brands and re-branding.
Your first description does sound like a cold or fractured solder joint.
If you've had the board out, do it again and inspect the HV area with magnification for solder joints that look cracked.
You didn't mention how old the box is and if it was built in the 2003-2006 period, you may be a late victim of millions of capacitors which failed because of counterfeit and defective electrolytic solution.
Sorting out the good and bad caps needs patience and a cap meter with DF (losses) feature.
Locate the main power supply transformer; it will be about 4 cubic inches and the core will appear smooth (ferrite).
Check the diodes you can identify near that transfomer, you may have to lift one end of some of them since the ohms (or diode) reading you see may have a low-resistance winding parallel and a low resistance load to ground.
It sounds like the PS output for the HV circuit has failed but that may be a symptom of the problem, not the origin.
You've checked the horizontal output transistor (2S)D2539 but made no comment about what you found.
This type has an internal damper diode that can make it look bad if you aren't familiar with it.
Two of the three leads should be desoldered and centered in their mountng hole so they are not contacting.
Pinout is here:
(This is for a replacement type of the same ratings.)
Checking from E to C; with the positive on the collector, the negative on the emitter, it should measure quite high, maybe infinite is all is well.
Reversing the leads will probably show a typical diode drop of something less than a volt (the diode function is supplying current but measuring and displaying a voltage drop of ~ 0 to 2000 millivolts).
The base to emitter and base to collector MAY show values quite close to each other, hundreds of millivolts when the positive (it's an NPN type) is placed on the base and the negative on the other two - separately of course!
Posted on Jul 05, 2008
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