HMV 2638- Another 960

[Focus Diode]

David and I landed back in the North East with a new addition, thanks Steve, of another Thorn 960 set!

The front styling is similar to the earlier 2633 though in "negative" form. The chassis is the later version with a dropper resistor and card rear back.

Now, the temptation to keep the set for spares has to be resisted, even if its older brother has a 3 minute warm up sequence. This model deserves to live in its own right.

Removing the chassis from the cabinet revealed a much improved feature; the CRT is properly Feinbridge guarded as found on 29" and 23" models, not the crude sheet with the CRT face resting on it then secured by a plastic cradle. Seems the best dust seal efforts won't prevent dust entering between the sheets and CRT face. I'm working towards CRT removal, a completely unprotected type, to clean it again. Not a nice job that would have been avoidable had a proper guard been used.

Anyway, back to this model in question.

Apart from a 1960s Mullard PCL85 the valves otherwise looked to be the original. The Mazda PL500 even had a version of the Mazda logo deemed vintage by the mid '60s.

Because everything had ceased up through rust I felt application of WD40 was justified in this case to free the system switch and UHF tuner mechanism, though it'll be awhile before I attempt to change systems via the solenoid.

The mains filter capacitor is situated under the on-off switch requiring chassis removal for access. This will be replaced when the next component order arrives.

Cold checks revealed nothing amiss so thought I'd wake it up via a lamp limiter.
Only evidence of life was a dim glow in the EF80 on its sub panel.

A further tests revealed a rather nice firework display within the PL500. Fit replacement PL504 and PY801s before proceeding further. Not unexpectedly the rusted original PY801 top cap came off with the valve.

Things very calm on the next test. After a few minutes try on full mains. Line lock miles out, bottom cramping and violent unlocking of the frame greeted me with hum on sound. As a quick test a known good PCL805 was tried making no difference at all so the valve itself could be ok. At this point the sound completely failed with the PCL86's cathode bypass electrolytic overheating. Fitting a new PCL 86 restored the previous sound with hum conditions.

So a lot of work to do which I'll soon be starting on the frame and sound stages, then go on from there.

The CRT certainly looks to be in excellent order.

[Focus Diode]

And here's first light. The black bar is from the camera, unable to cope with the rapid frame unlocking.

I'd forgotten how intense the 405-line whistle is with the original red jellypot Lopt.

[Focus Diode]

Negative cabinet colours?
Well, almost!

[Colourstar]

Very good work Brian. How is the crt looking in terms of emission?

Steve

[Focus Diode]

Hi Steve,

The CRT looks to be excellent.
Did a bit of work tonight including replacing R98 which solved the frame lock problem yet otherwise the linearity is as bad as ever.

Much time was wasted investigating a new fault- fuse blowing at switch on. Thinking I'd caused a major HT short I checked the work done to no avail. Three fuses later I found a chassis connecting lead was touching one end of the HT rectifier.....

We all have our off days.

Cheers,
Brian

[Focus Diode]

Yesterday on clearing the HT short the initial image was stable, allowing for the frame cramp. It soon became this wobbly mess.

I've had this one before, C43, 0.1uf sync separator grid coupler.

Like the other similar capacitors on the main board, they'll all have to be replaced.

[Focus Diode]

Good progress this afternoon. Replacing the components around the frame output transformer gave full scan with the expected wobbly verticals. Replacing C43 cured that as expected.

It's looking good! Much more work to do of course.

[neil29]

Its good to see a picture on it at last as I never bothered with it or the 1400 I bought from camber sands. and I did wonder whether they would need much doing to them when I walked into the shop thinking they had been badly stored.


Cheers
Neil.

[Focus Diode]

It's amazing how well they come up in spite of less than ideal storage conditions. There's a lot of internal rust, the volume control has ceased solid so will need replacing amongst other work. At least the system switch is now free so will see if the solenoid works and assess the performance on 625-lines.

There is of course some lack of width but I'll leave the line output stage well alone until I receive an order for 1KV rated capacitor's which will include the mains filter of course.

Cheers
Brian