Possibility of repair for Sony KV-21X5U CRT TV

[inse]

The most universal type is the S2000, but you will be more safe keeping to the original type.
Its a matter of will for tinkering and price/availability as well.
BUT its also worth finding out why the HOT had failed as described already before.
Better buy three transistors at once as they will immediately tell you that you forgot checking something...

[HwAoRrDk]

Oh yes, I will buy more than one, just in case.

Is it worth checking the horizontal drive transistor (on the other side of the transformer T531), Q535?

What kind of frequency will the horizontal deflection drive signal out of IC301 (the 'jungle' chip) be? Just wondering if I'll be able to scope it using my battery-powered (and thus isolated) 'toy' oscilloscope. It's only good for <100kHz signals. The schematic shows what kind of waveform and p-p voltage to expect, but not what frequency/period it should be.

Edit: I de-soldered Q535 and measured it. It's a 2SC2688 NPN. It measured as follows:

B-C: 0.6V
B-E: 0.61V
E-B: OL
C-B: OL
C-E: OL

That all looks good I think, probably nothing wrong with it, so I put it back in.

[wasedadoc]

What kind of frequency will the horizontal deflection drive signal out of IC301 (the 'jungle' chip) be?

The drive signal will be horizontal sweep rate. 15.750 kHz for NTSC.

[inse]

When you have the new transistor and solder it in, leave the collector open or interrupt the B+ somewhere else.
Then scope the base signal, compare it to waveform 10 in the service manual.
Then check everything upstream of the collector up to the B+, all the f... diodes and capacitors.
After that you are ready to sacrifice the first HOT.
There is still a chance the FBT is broken.

[andy2000]

Some Sony sets often had cracked solder connections on the horizontal drive transformer.  This would intermittently cause the output transistor to fail.  It's a good idea to resolder it just in case. 

[HwAoRrDk]

The drive signal will be horizontal sweep rate. 15.750 kHz for NTSC.

This is a PAL set. Although... I suppose that'd only make a difference for the vertical sweep rate?

Then scope the base signal, compare it to waveform 10 in the service manual.

Just wondering, will the form of the base signal depend on whether there is any (or what) video signal being displayed?

Some Sony sets often had cracked solder connections on the horizontal drive transformer.  This would intermittently cause the output transistor to fail.  It's a good idea to resolder it just in case. 

Thanks for the tip, I will inspect those solder joints closely. In fact, will give the whole board a good look over.

[wasedadoc]

The drive signal will be horizontal sweep rate. 15.750 kHz for NTSC.

This is a PAL set. Although... I suppose that'd only make a difference for the vertical sweep rate?

. 625/50 horizontal rate is only slightly different. 15.625 kHz. 64 microseconds period.

[eurgenca]

Hello.
Please check bad solder joint on FBT and C531 and C545 for ESR.

[HwAoRrDk]

When you have the new transistor and solder it in, leave the collector open or interrupt the B+ somewhere else.
Then scope the base signal, compare it to waveform 10 in the service manual.

I got a couple of new S2055N transistors. I took the precaution of measuring the new ones too - when measuring B-E/E-B on diode test the meter would still beep for continuity, but measuring resistance they were 40 ohms, which is close to what the built-in B-E resistor is supposed to be (50 ohms), and everything else checks out, so they seem to be good.

Bent the collector pin up and out of the way and soldered one in. Probed the base pin with my scope, as well as measuring the B+. The B+ was a solid 135V, and I got a regular-looking waveform of approx. 15.67kHz on the 'scope (see attached image). Voltage seems a bit low compared to what the service manual says, though. I got 4.7V p-p, and it says 12V.

No magic smoke released or anything, so it seems to be happy so far. Interestingly, about 10 seconds after power-on, it started flashing another, different error code on the LED. This time it was 4 flashes, which apparently means "no vertical sync" according to the service manual.

I gave the board a good look over for bad solder joints. Looking very closely at the horizontal drive transformer (T531), it seemed like there might be a very small hairline crack around one of the pins, but it was very hard to tell. I re-soldered all the joints on it anyway as a precaution.

Anyway, that's all I had time for this evening. Tomorrow I'll solder the transistor back in fully and see how it goes.

[HwAoRrDk]

Soldered the transistor back in completely, and... it works!!

Picture looks good, no distortion, B+ is still 135V, 'scope shows an actual proper 15.625kHz for horizontal drive (not sure why it was slightly fast previously), mains power consumption is approx. 0.5A (although I haven't hooked the speakers back up yet).

I did have to scrounge around for a while looking for some fresh thermal grease when properly re-fitting the transistor, but managed to find some in a box of old computer stuff.

Thank you everyone for your help, particularly inse.

[inse]

Triple thumbs up!!!