1974 22" Ultra 6714: Thorn 3500 chassis

Well I waited almost 1 hour, powered up again, it came up with line lock at 15,625kHz. Left it on for an hour monitoring the line oscillator, the frequency remained steady no wavering whatsoever. I can't think what was happening the first time. What might have cleared all I did between the first attempt and second was to remove the core from L501 completely, blew out chamber and refitted. Hardly see how that would do anything.

Did a quick adjustment now TCF is looking a little more geometrically acceptable but still work to do there.

It looks like the decoder is working as I have colour, that's a plus. First thing I'm going to do is replace the 'Thick film' on the video board to see if that clears up the all red problem.

More to follow.... 

I wonder if there could have been some damp in the oscillator coil (or somwhere else) that's dried out with use. Maybe that's all it was.....

Removed the video board and gave it a good clean. The board is as far as I can tell, virtually untouched, looking at the rear all the solder joints seem factory. Anyway I went over the whole board with the ESR meter checking all the electrolytics. All were OK, a few were borderline and with use likely will need changing. 

Found a NOS 'Thick-Film' unit in stock so soldered it in and tested. The red overkill was gone replaced with a ghastly mess, I would hazard a guess as this thing was dying the RGB A1's were adjusted to compensate. Did a rough and I mean rough twiddle of the A1's to give a reasonable picture.

Not looking too bad, needs grey-scaling and some convergence. I will go through all the set-ups on the video tomorrow.

Some might be screaming at the screen now, "Change the Film unit, modify it back to the more reliable six resistor configuration". I agree the film units were not the most reliable of components and can lead to intermittent Grey-Scale drift.

For those slightly interested and not sure what this means, to improve reliability you just install six individual resistors, three 12K 7W and three 56K 1W.

These are as follows:- R259, R264 & R277 (12K) R249, R263 & R276 (56K)

However I'm not going to do that, why not you may ask? Well I've done the mod on other 3500 sets and I want this one to run as an example of the technical progression/life-cycle of the 3500. Its not going to be run 7 hours a day so it wlil be fine. If we modify every set then there will be no examples of the film unit in action and that's erasing history.

The body count to get to this stage is very low and once I've done the set-up, that's how I will leave it. Fix-on fail after that as I've said often, I prefer to repair than restore. 

All coming together very well, excellent work, very impressed.

Frank

The early 3000 sets had individual resistors fitted.

I know 

chris said

Some might be screaming at the screen now, "Change the Film unit, modify it back to the more reliable six resistor configuration". I agree the film units were not the most reliable of components and can lead to intermittent Grey-Scale drift.

For those slightly interested and not sure what this means, to improve reliability you just install six individual resistors, three 12K 7W and three 56K 1W.

These are as follows:- R259, R264 & R277 (12K) R249, R263 & R276 (56K)

However I'm not going to do that, why not you may ask? Well I've done the mod on other 3500 sets and I want this one to run as an example of the technical progression/life-cycle of the 3500. Its not going to be run 7 hours a day so it wlil be fine. If we modify every set then there will be no examples of the film unit in action and that's erasing history.

Phew! I'm glad you got there in the end, those CCL caps here were very troublesome but usually causing an intermittent line speed twitch.

Thorn pushed on with thick film units with even more complex designs as used in the 4000 but I wonder if anyone ever saw one of the last gasp 3500 sets fitted with the hybrid thick film module on the Frame & Sound PCB? This contained the field osc and driver stages, didn't see many and don't recall ever replacing one.

John.

You have the NOS modules, may as well use them and keep it original. Has you say it's not going to have heavy use. I remember in other makes the thick film resistors were unreliable. I am correct in remembering they were used as a way of keeping the components well within tolerance of each other under varying environments?

Frank

Removed and cleaned the decoder then tested all the electrolytics, all were OK. Only one on the board which might need changing if the set gets continual use, until it starts to cause trouble it will stay.

Set the CRT grid bias and the did the grey-scale tracking, as they say, "get it right in black and white". Way improved over lasts nights results, still some convergence errors to work out and I'm going to have the convergence panel out to apply some servisol to the presets. 

Starting to come along quite nicely now.

More to follow.......

Looking at picture #3 reminded me of my one dalliance with a 3500 - that it was a right royal PITA to get good blue convergence.

Looks a bit out of focus too, perhaps a tweak may help sharpen up the blue ? 

Well time to bring this thread and Ultra 3500 repair to a close. I've finished removing, cleaning and testing the remaining boards namely the Frame/Sound and I/F panels. Running the ESR meter over the electrolytics showed them all to be within tolerance. I did a final grey-scale and convergence moving any errors as such out to the edges as you're supposed to.

For a fairly ratty ( literally) high hour set which had lets be fair. a knackered CRT. Now rejuvenated its giving the best account it probably can. 

Oh and the first picture shows what a coward I am when it comes to sticking ones hand near the EHT cable which carries 25kV. Yes that's a square cut from a hot water bottle, don't all laugh at once.

That my friends, concludes the 1974 Ultra 6714.

Next on the bench? You'll have to wait and see. I have a batch of 3k Line time-bases to repair so I may just jump on over to the workshop section and do some Jig repair sessions to those. Then again an 8800 is calling as is the monster 3500 Marconi, we shall see.

Oh and I had the Ultra running for 6 hours straight over the weekend, the flyback tuning cap I used was cold to the touch. I highly recommend them as a replacement source.

Please Sir, can we have something that isn't a Thorn, Sir...?

I'm curious about that Decca CTV22C you have.

I'm waiting to see the Dynatron CTV 18 up and running

Hi Chris

Well done , another excellent restoration . I have the same model which came from a friend of mine in Kidderminster . 

I do hope that your 8800 is next on the bench as i have an ultra version which i have yet to start on so we will be able to compare notes .

Regards .

Gary .

Hi Chris,

Yet again another good job done 

Roll on the next project !

Marc.

I've been following this with interest. Great work Chris and a very good result on a set that not that long ago would have been considered hardly worth bothering with. How times have changed. We have to take what we can get these days!

A school friend's parents had the exact same Ultra set teamed with a Panasonic NV333 (I think) VCR. That would have been about 1984, so it was getting on a bit even then.

Steve

I am glad to hear your Flyback cap is holding up

Another comprehensive and interesting write up, thanks.

Well done Chris!

Another superb set sorted 

Excellent restoration job, well done.

I'm pleased I kept quiet about the very red picture. Our rented Ultra developed this problem in 1976, originally intermittent but became permanent with gross red fly back lines to add to the drama.

The Rumbalows field engineer was present when I got in from school. He'd been there for sometime replacing panels to no avail. He took the set away and left us a nice GEC 2110. The Ultra's CRT had to be replaced.

The 2110 was altogether a much better set, it allowed constant colour pictures from Yorkshire tv the Ultra could only manage when conditions were good. Unusually for a Thorn set gain wasn't very good in the 3000 series. Doesn't matter nowadays of course.

cheers

Brian