Has anyone worked on Sony Power Supplies for television sets here? I have a 32" Sony 1999 kv-32s42 find. The power supply uses a dual bipolar transistor design coupled with two transformers and some capacitors to form a power oscillator for developing the B+. It looks like the two NPN transistors , actually it is ONE case with TWO NPN transistors in it, called a mx0841ab-f.

Using EchoWars's transistor diode equivilent test, both read ZERO all six ways each, and on a conventional ohmmeter, I get less than one ohm all six ways each. Looks like they're dead, BUT has anybody done something like this before?

The circuit is common across Sonys, I have a 20" Sony 199(8,9??) tv with the same setup, but a slightly different part number. I also found computer monitor schematics with the same setup. I just don't have the intestinal fortitude to open that set up, remove the similar part and make comparison readings.... (It's my "daily driver").

I also don't like the readings I am getting with the Horizontal Output Transistor, AND upon removal, the heat sink grease only covered the top of the tab area, NOT the body where the heat was produced. No surprises on THAT failure.

I know about the kits for Sony parts from B&D enterprises, which has both the dual transistor and the H.O.T. for about 20 bucks.

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The original cause of failure is bad soldering on the horizontal drive transformer which takes out the HOT. It should be ok after replacing the HOT and that dual transistor. There's also a .1 ohm resistor in the power supply that will be open (it protects the fuse).

There's also a .1 ohm resistor in the power supply that will be open (it protects the fuse).

...thats thoughtfull of them.

Thank You Andy, Yes, I know about that resistor/fuse, .1 ohm 1/2 watt, mounted in eyelets on the board. It's open.....
Part number fnf12nr10ku (sony 1-202-933-61) , and it is part of bdent.com's kit #4 which I ordered.

This seems to be a newer chassis, as some of the solder joints to the board that I would consider stressed by either component size, or thermal dissapation of the component have eyelets installed in them, increasing the solder contact area, as well as providing a mechanical backstop for movement on both sides of the board.

I have checked the Horizontal Output Transformer solder joints, and while (to my somewhat expert eye) they seemed good, I cleaned out the old slobber and put in some good Kester 44 60/40 . (The old crap actually outgassed as I heated it).

When I removed the Horizontal Output Transistor, I found that only the tab area of the transistor (25 - 33 % of total area) had any Thermal transfer compound on it AT ALL. Can you say "OVERHEATING" ???? I don't blame it for going belly up..........

My only hope was that that expensive dual transistor in the power supply was good, despite the readings that lead me to believe it is shorted. It would be a real kick in the shorts if the new one I ordered reads the same.

The DRIVE transformer is not the same as the output transformer. It is the little 4 terminal transformer on the base of the HOT.

Something caused the HOT to short. It may have been the lack of good thermal contact with the heat sink. Hopefully it's not something less common like the flyback. It sounds like that double transistor is definitely bad. It should test like a pair of normal NPN BJTs. I wish there was a way to test these sets without risking another power supply rebuild! Most power supplies aren't damaged by this type of overload.

The DRIVE transformer is not the same as the output transformer. It is the little 4 terminal transformer on the base of the HOT.

Absolutely!!! Nakdoc, my bad, mis-spoke there, the DRIVE transformer (T501), OUTPUT Transformer(T502) and FlyBack Transformer (T503) were checked, as well as the HOT's base resistor, actually the FORMER base resistor, now specified as (and IS) a 7.5mm jumper. The 3 damper diodes and a pile of other components in the circuit were also checked.

The kit is coming UPS 2nd day air and the weekend interfered, so I won't be getting it until Monday... oh well....

I have located multiple sources for the FBT (~$20), if I have to replace it...

I will report back with the readings of the good (and bad) components when available, and either whether it works, or needs more work...

I'M BAAAACK.......... as promised

It's up and running :banana: :banana: :banana:

As promised here are the readings of the MX0841AB-F dual npn transistor (Sony 8-279-041-12 )
the bad one reads 0.000v forward drop all the way round, and 0.4 ohms on a genuine ohmmeter.

The new part reads as: with the leads arranged left to right:
(r is red (+) meter lead, b is black (-) meter lead)
e.b.c...c.e.b....
r.b.................OL
..b.r...............OL
b.r.................537
..r.b...............474
r...b...............OL
b...r...............OL
.....................
.........r.b........OL
.........b.r........OL
.........b...r......475
...........b.r......538
.........r....b.....OL
...........r..b.....OL

thus it reads as a pair of normal NPN transistors

and for the Horizontal Output Transistor, it reads normal now too.

So the power supply dual transistor, the hot and that .1 ohm "fusible" resistor were replaced, with the failure being caused by insufficient heat sink grease on the H.O.T. resulting in the the lack of good thermal contact with the heat sink.

Thank You for the assist folks!!:D

Thus one curbside find, of a 1999 Sony 32" TV on New Years Eve, LIVES AGAIN!!!!

I'm glad it worked out for you! I'm getting ready to do the same thing with a Sony that i have. Its the older 32S26 but has the same problem...dead as a doornail. I hope mine repairs as easily as yours did.
-Tony