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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old Yesterday, 2:27 am   #21
space_charged
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Default Re: Sony 2SD625 line output transistor

The frame timebase is now running. There were two defunct transistors, Q552 and Q553. Q553 is one of the frame output transistors so needs to handle a bit of power and needs to be reasonably high voltage because of its inductive load. I used a BU806 for that. Probably "overkill but I had them laying around. Q552 is a small signal NPN so for that I used a BC337.

There is no raster (yet). I had assumed that might be because of some sort of safety device operating if there is a frame collapse. Next step will be to check the various voltages round the tube base.

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Old Yesterday, 11:37 pm   #22
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Default Re: Sony 2SD625 line output transistor

Latest on the restoration of this KV9000 is that a nice colour picture is now being displayed on this set. The residual fault turned out to be an o/c resistor R353 in the collector of Q305 (pnp transistor). The effect of that was to bias off all three cathode driver transistors so nothing appeared on the screen.

It was then found that the brightness pot itself was o/c from the centre terminal to either side. Disassembly shows the wiper had corroded away. A couple of fixed resistors are currently in place and brightness adjusted by the G2 pot on the tube base. A replacement 5K pot is on order.

I should say that this set was in a very bad condition with a lot of rust on all the metal. The tracks and component markings were invisible on the timebase board copper side. Looks like the set had been in damp/wet conditions. The timebase board copper side was painstakingly cleaned with cotton buds moistened with 50% isoprop.
The screening cans on the main board below the timebase board were very rusty and had to be cleaned. The brightness pot was also rusty and had failed.
I originally bought it only to take some parts from. Tube, LOPT etc but cleaned it up a bit and cautiously applied power. One by one the faults were repaired and the result is a working set.

The set can run from either a 12 or 24 volt battery and at the moment I am running it from a current limited 12V bench supply. Next step is to test out its mains supply, which is a 24V conventional transformer. I am slightly worried about the condition of the mains transformer, given how wet I think this set has been in the past.

Photos attached show it on the bench. The RGB cut-offs and the green and blue drives need to be adjusted.
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Last edited by space_charged; Yesterday at 11:54 pm.
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