Sony KV1320UB Mk1

[Tazman1966]

Well...it's been a while since I asked for help but here's a request.

A friend of a friend who's a bit of a retro freak recently acquired this old Sony set and asked me to give it the once over.

As old Eugene Trundle would have said in Television magazine, it had been twiddled from black level to teatime! It was also covered in a thick carpet of dust in places well over an inch thick!

I gave it a light brushing out and vacuumed the dust away to reveal quite a clean looking chassis.

After a lot of undoing the work of the phantom twiddler, I was left with three faults:

1. Weak sync, both line and frame including sometimes wobbly verticals although that aspect is intermittent.

2. The picture is very much darker on the left than the right and there is some white streaking from low-lights and black streaking from highlights.

3. The raster size sometimes keeps changing in both aspects. I've measured the 115V line and it is totally stable.

Any initial ideas and possible stock faults from any of you? I'm no Sony expert!

Thanks in advance.

[Studio263]

The darkness of one side will be a crumbly cap on the panel that hinges down at the back, I can't remember if it smoothes the supply to the RGB stages or to the A1s but there are only a few there to check, it's 10uF 350V from memory, something of that ilk anyway.

For the picture size changes check the EHT rectifier valve and its holder. I have a spare (new) one if you get really stuck, it's a Toshiba version of a GY501 but with more pins for some odd reason.

Sync: that one jiust needs working through but may clear when the capacitors on the rear panel are dealt with.

[Tazman1966]

Thanks Tim. I've PM'd you by the way.

[bobbyball]

That's (otherwise!) a good picture for a MK1, most have totally flat tubes by now.

If I am not mistaken, this is the version with the large transformer that provides, I think, 110 volts, but also on this version, and again unless I am mistaken, the tube heaters are left on when the main set is off... I think the rectifier valve is a 3AT2 from memory...

[Studio263]

Originally Posted by bobbyball

and again unless I am mistaken, the tube heaters are left on when the main set is off...

Only in the early ones and then at a reduced power, the chassis was soon modified to remove this function. A quick way to tell which you have is to look how many wires run between the mains transformer in the rear cabinet and the rest of the set; if there are only three then the heaters stay on, if there are more than that they don't.

I don't know how much this arrangement contributes to the aging of the tube, after all the KV-1310UB / KV1330UB (etc) don't have it and they are mostly encountered with flat tubes these days.

[Tazman1966]

On the money Tim!

First the shading and smearing. Sure enough it was the RGB smoother/decoupler electrolytic, C613. The other two electrolytics, C612 and C615 on the board were also oozing so were changed too in order to avoid later trouble.

Onto the sync problem. By now the fault had become permanent with very weak frame and line sync and wobbly verticals - it looked as if picture information was getting into the sync signal. I followed the feed to the sync separator (Q459) back to the signals board and with an air of confidence, changed the 1µF coupling e/lytic but no change. There were a couple of e/lytic decouplers around the sync separator transistor which I suspected but these were faultless. Tim had suggested that the biasing of the transistor may be at fault and to check the resistors nearby but all read okay. Transistor maybe? A weird Sony PNP one. I noticed that it was bent over almost double. Just for the hell of it I straightened it up while the set was on and suddenly the sync was perfect! What was going on here? Had there been a dry joint all along that hadn't responded to any kind of tapping? I remade the connections just in case. Maybe something weird was going on inside the case of the transistor. In any even, I can't make the fault reappear although I may (when I get a suitable replacement) change it anyway.

As to the bouncing picture, sure enough the pins on the 3AT2 EHT rectifier valve were well manky! With them cleaned up all was well with the EHT.

A final tickle up on the convergence and grey scale a thorough cleaning of the cabinet and controls and that was that. The red gun is very slightly lower than the rest but hardly. Here's a couple of pics of the old girl in action.

Thanks again to Tim for the information and inspired diagnosis and to Bobby for the additional comments.

[threeseven]

Spot on, good job! I have on of these too, off freecycle! Fortunately fully working with an excellent tube! The giver had owned it from new and was annoyed that his wife had thrown out the original box only the week before! Justifiably well acclaimed sets from a users perspective but can be tricky to service.

[Focus Diode]

Excellent result Tas, well done. Surprisingly good colour in view of the modified NTSC circuit employed.

Cheers,
Brian

[bobbyball]

I knew I would be "corrected"!!

At least I remembered the 3AT2 valve! The transistors in these and similar (eg the KV1800) sets can suffer from a sort of "tarnishing" on the legs and often go noisy. Type 2SC1128 springs to mind.

Other than flat tubes and dying caps these sets are pretty bomb proof and, with a good tube, still give modern stuff a run for it's money. Even the odd decoder gives a decent picture when set up properly. Nice work...

[Nickthedentist]

Originally Posted by Tazman1966

On the money Tim!

No surprise there!

Looks lovely, Tas, nice work.

Nick.

[Tazman1966]

Thanks again chaps.

I thought I'd give the set a good run this morning before work (I'm on 1400 until 2200 shifts this week) and the sync twitched a few times after it warmed up and then shortly afterwards reverted to its previous fault condition. I left it like this for about ten minutes and tried some tapping of the cabinet but it seemed permanent so I set about removing the back cover to give the transistor a shove to make absolute certain that it was that which was the problem. Eleven bloddy screws to undo and by the time I'd done that and pulled the brightness and vertical hold knobs off in order to remove the cover, the fault had cleared! I will replace that transistor as I'm still almost 100% certain that will effect a permanent cure.

Ha! The fault has reappeared. Tapping the board in the area around Q459 did nothing but pushing the transistor and bending it over slightly stopped the shenanigans straight away so fault confirmed

[Hybrid tellies]

Nice one Tas. Wish you luck finding a replacement or equivalent transistor

[Mikey405]

Well done Tas. Looks like a tip-top job to me.

[Studio263]

Originally Posted by Hybrid tellies

Nice one Tas. Wish you luck finding a replacement or equivalent transistor

More or less anything will do in these low level stages, I use BC547 / BC548 (A, B, C etc, it doesn't really matter) for the NPN ones and BC557 / BC558 (...) for the PNPs. There is nothing special about any of these, they are just the ones I keep as they seem to work in just about everything.

The only thing to watch is that the pinning is often different; Japanese transistors usually have the collector pin in the middle where as normal European practice is to put the base there.

[Tazman1966]

Thanks chaps. I'll look out for that Tim.