Dead Sony KV-1200U

[freakaftr8]

Hey guys,

I didnt wq\anna resurrect an ol thread but this Sony's one I talked about before, just thought while im waiting for parts to come in i'd take another whack at it.

Well I can say the CRT's not the best, a bit on the pink side, I can tell this one's had some use. Well 20 minutes into it, (hooked up to cable) it went dead. Popped the circuit breaker in back of the set. So I turned off the power, reset it, popped it again immediatly. Well I checked the breaker to be weak, I have some in a bin and replaced it. It blew the 250v 5a fast acting fuse. THe slo-blo is still good.

So now imn thinking, hmm shorted filter cap. I did a quick ESR reading on the can and it tests in the limits, then I tested the other caps around the HV, all seem well in limits and no shorts. I did find a 6.5v 1000mfd cap on the vertical board at 1800mfd, so I replaced it. HOT and other various transistors and diodes test ok.

Any ideas what might be happening w/o a schematic?

Here's the old thread from Set of last year.
http://videokarma.org/showthread.php...=sony+kv-1200u

[kx250rider]

I wonder if the HVR block shorted? That's VERY VERY common. In fact, I have a KV-1200U here with a bad HVR.

To test it, you need to remove the 3A3 and see if it still blows. If not, your HVR block is shorted.

Charles

[freakaftr8]

Got it, i'll give it a go and see what happens, and where is the HVR block, are these the 2 transistors within the fly cage?

[kx250rider]

Originally Posted by freakaftr8

Got it, i'll give it a go and see what happens, and where is the HVR block, are these the 2 transistors within the fly cage?

You can see the back of it here.. Follow the anode lead and it's the red plastic box on the right in the photo... It may be slightly different on your KV-1200, which is a year earlier than this 1201.

Charles

[freakaftr8]

Hey guys
Well good news. I dont think the HVR is bad, I replaced the fuse and pulled the HV rectifier tube and the fuse still blows. When I pull the rectifier does this rule out a shorted HOT or yoke?

[freakaftr8]

The odd thing that I forgot to mention is when I do turn it on before it blows the fuse I hear a high pitch whine, like HV or something.

[andy]

---

[freakaftr8]

All the transistors, B+, HOT, and the one next to it, both rated the same specs, probably CONV, all test good. Caps are not shorted, all test ok on ESR, the 160v 470MFD is like 530 though. Fuse still blows with no rectifier tube installed. And now I used to get a whine upon startup and a quick blip of audio. Now I dont even get a whine or audio, just blows fuse. I think I might give up on this one again fgor a while and put it in the closet. I do have a working 1220U with a good CRT.

[kx250rider]

It doesn't necessarily rule out the flyback, but you can narrow it down by unhooking the collector of the HOT. In that set, just take the screws out of the HOT retainer ring, and the collector is out of the circuit (screws are the connection between the collector and the circuit).

If you unhook the collector from the HOT and the short is gone, next scope the horizontal oscillator at the base of the HOT to see if it's running, and also if there's crap in it (a rounded peak or a disturbance making it not a nice sharp sawtooth). If the waveform is fouled, it's maybe another electrolytic someplace in the B+ feeding noise into the oscillator, or an electrolytic squashing the peak between the oscillator and the HOT. If all that looks good, but it still blows with the collector hooked back in, then it could be an FBT problem or hopefully a dead short on a secondary line of the FBT.

Charles

[freakaftr8]

Ok cool, i'll check that out tonight.. I was thinking about disconnecting the HOT, but was not sure if it was going to do more damage then good. Technically, I don't know why im working on the set, it does have a weak CRT visually. I got no way to test trinitron CRT's with a meter. My sencore can test single gun CRT's but I lack the adapter.

[freakaftr8]

Ok well it seems the fuse still blows then I removed the collector off both tansistors in the fly cage.

[freakaftr8]

I have the high pitch whine and audio before the fuse blows again, after i reinstalled the HV rect, Is the HOT one of those 2 transistors in the flyback cage? Both of these NPN sony transistors are C806A.

[freakaftr8]

Well the situation with this one got worse.. After I tried a power up again, I got a bad fuse that wouldn't blow, instead, I think l lost the B+. I have a light on the tuner, and I hear the degausing field but thats it, so sound and no high pitch whine.

[freakaftr8]

Hey all. Has anyone worked on this set before possibly know if B+ is derived off the flyback? I think the 2 transistors in the flyback cage are not HOT, they are for B+. Am I right? There is a transistor on the bottom of the set, it's smaller than the TO-66 transistors, there is also one on the chroma/vert/horiz osc board.

Possibly a schematic?

[kx250rider]

Originally Posted by freakaftr8

I have the high pitch whine and audio before the fuse blows again, after i reinstalled the HV rect, Is the HOT one of those 2 transistors in the flyback cage? Both of these NPN sony transistors are C806A.

Q801 is the HOT, and Q802 is the converter; both 2SC806As. I'm looking at the schematic now, and I see 3 mylar caps, and the damper diode (D801) are still in the circuit when the HOT collector is disconnected. I've seen those caps short, but you should see that as a short to ground from the collector. I can't remember if you checked that and said?


The B+ comes from the emitter of Q903 (2SD69). I think that's on a heat sink, mounted on the chassis frame, if I recall (no pic in the book). It's a basic linear supply, with only a bridge, filters, Q903 to regulate, and Q601 (2SC867) as regulator driver. Those short OFTEN! I'd check that first. If it's blown, you likely have a load someplace which blew it.

How about I send you the schematic from the factory book? It's a very small manual, and I think all you need is the schematic and I can include the pages on adjustments. PM if you would like it.

Charles