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#1
06-30-2014, 11:53 AM
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sony xbr d board problem
Hi guys. I have been trying to fix a kv-34xbr910.
So, I replaced the mosfets which were all shorted, one fusable resistor, both I'c (now socketed) and the thermistor. set was up and running! I bought a pattern generator to do an alignment, and when I powered it up again with the rear cover off, I saw a bit of light and then it was doing the 6/7 flash routine again. I remember that flash from earlier troubleshooting so pulled the board and sure enough a fusible resistor went. also 2 of the mosfets shorted out again. I replaced them and now the set is still doing the 6 blinks. I'm very unhappy  What could cause this board to eat mosfets like that? I'm out of spares (mosfets and Ics). I don't want to trash this set. I have spent a lot of time and a fair amount of $ on it by now.
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#2
06-30-2014, 12:12 PM
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If I remember correctly, there are some snubber capacitors that open up on the MOSFETS. When these go bad the MOSFETS will last a short time and fail again. Did you put sockets on the ICs? It makes life easier.
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#4
06-30-2014, 03:31 PM
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Also==did you use SONY replacement parts for the FET"s ? Sony sets do NOT like generic parts at all. And the thermistors/VDR's--MUST be the sony #s or you will get what you did. Been there...DOME THAT1!
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#5
06-30-2014, 05:04 PM
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the mosfets were genuine sony pulls. The thermistor is a generic. it measures the same as the one that came out. Same part number, different color. I can't find any more of those mosfets in my collection and can find no source for them.
Any ideas?
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#6
06-30-2014, 05:26 PM
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Also the 4 mosfets that originally failed, the two IC's and the thermistor were the original sony parts. Apparently this set does not even like it's own parts. Very few parts in this set are actually made by sony. Some of the chips are
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#7
06-30-2014, 05:27 PM
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If...that "thermistor" is the one off the gate of those transistors--it is NOT a thermistor, but rather a VARISTOR_-and you MUST use the original # on it--or the Sony #, I recall trying a generic varistor. It came up--I got HV for maybe 3 seconds...then BANG !! Out went everything !!
ALSO--make SURE nothing went in the horiz out area, such as the h-out--even if this set uses a split deflection system--it STILL uses a H out transistor.
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#8
06-30-2014, 06:01 PM
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No it was a thermistor in another circuit. It just makes the set error out if the transistor it is near gets too hot or it drifts out of tolerance. I have the schematic. The gates come off pins 12 and 16 vg(l) and vg(H) then go through a series 10ohm resistor then parallel a couple of sm chip diodes and a 10K ohm sm chip resistor
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Linear Mode
