My Thorn 2000 back after 34 years!

[toshiba tony]

People were scared of the 2000\3000\3500. But access was easier than the 8000 and 8500 series. I only ever saw one 4000. Now they were nasty. Sorry if off topic. When it comes to old tv's I'm putty.

[greg_simons]

Originally Posted by 1100 man

Hi Greg,
I've still a way to go yet before considering it as 'finished'! The next task is the poor EHT regulation. It will be interesting to try your EHT board to see if that makes things any better. I still have a feeling it's going to be the tripler though. If the Selenium sticks have gone too high resistance, the control circuit won't be able to increase the drive sufficiently to keep the EHT at the correct level.

Rebuilding a tripler with Silicon diodes will be a project in itself!

Glad yours is going well- how long until you can get some power to it? It would be good to see some pictures of your cabinet just to see how bad it is!

Cheers
Nick

Hi nick
Got to get the chassis frame up to the house for a check and clean, realistically perhaps a few weeks. depending on how it goes with the chippy, I will go for power up regardless of how the cabinet is just so long as there is enough structural integrity left that it doesn't fall to bits while being moved, I'll do some pics this week coming and you'll see what I mean.
Greg.

[Welsh Anorak]

I think I gave Greg a good tripler with the TV. When I say good, it'll be out of the same box as the tuner! There was also one that had been dismantled and rebuilt.

[1100 man]

I've just awarded myself first prize in the ' chasing a fault that isn't there' category!

Having ascertained that my nice shiny tuner works fine, I reconnected it to the 2000 and once again got absolutely nothing. The only difference was that the AGC line was now connected. Disconnecting it produced a weak, low contrast picture:- the penny didn't drop.

Assuming it must be an AGC fault, I jumped in with both feet. There are two transistors that deal with the AGC. VT9 (PNP), is driven by the output from the video detector. This is then amplified by VT10 (NPN) to produce the AGC line to control the gain of the tuner and also the first IF transistor.

VT10 was turned off so it's collector and hence the AGC line was sitting at 30V. This was because VT9 was turned on, as being PNP, it's base voltage was too low.

Chase round the circuit and discover that the contrast control supplies a standing bias to VT9. I wonder if that's faulty? Measure volts- plenty going in to the contrast control, nothing coming out, because, yes, it was turned down to minimum! Rotate contrast and, oh look, we've got a picture! Grrr..

My lashed in tuner, done when I was a kid, didn't have any AGC connected, so it was producing maximum signal. Consequently, the contrast control had been set at minimum to compensate. It therefore never occurred to me to adjust it when connecting the correct tuner!

So now on to the next issue which I think will be the very poor EHT regulation.

All the best
Nick

[Welsh Anorak]

I think that is the tripler, but it's not as bad as a rebuild - just a small excavation. I'm sure Television magazine had some article on how to do this.

[greg_simons]

Originally Posted by Welsh Anorak

I think that is the tripler, but it's not as bad as a rebuild - just a small excavation. I'm sure Television magazine had some article on how to do this.

Hi Glyn
Be interested to see that article, crusty on the vrat forum did one but the sealant cost a fortune plus no mention of where he sourced the sticks from.
Greg.

[Welsh Anorak]

I don't think it needed a stick - I think a resistor went O/C and could be located near the exit for the lead. Also ordinary sealant could be used as it was relatively low voltage. I'm sure someone's had a go at one of the triplers I gave you - might be worth digging as the others are likely to be OK.

[1100 man]

Hi Glyn,
I've felt all along that the poor EHT regulation is due to the tripler, but have not investigated it properly yet. At anything other than very low brightness, the picture balloons. There seems to be feedback coming from the VDR in the tripler, as when the brightness is increased, the supply voltage for the EHT generator output transistor gets cranked up. However, the EHT still falls.

Along with the tuner and other goodies, Greg gave me one of your triplers. It's the one covered in rough brown silicon sealer with both the input & focus wires missing. I've dug out most of the sealer, but can't tell if it's had new sticks fitted or not. My plan was to rebuild it with semiconductor diodes. Various people seem to have attempted this, but no one seems to have completed the project! Someone else found the EHT was way too high with diodes rather then Selenium sticks, so it looks like experimentation is going to be the order of the day.

However, I might try your one as it is and see if it works. It might hiss a bit though as it is now 'nude'!

All the best
Nick

[1100 man]

Now the darker nights of Autumn have arrived, I was seized with the desire to do some more work to the 2000.

I was interested to see if it would produce a picture on 405, so I manually operated the three system switches (there's no feed resistors to the solenoids at the moment) and switched on. After a bit of adjustment, a remarkably good picture of test card 'C' resulted, albeit with the hold control hard round to one end. I'd previously noticed that the 625 hold was also one ended. Replacing the three out of tolerance resistors associated with the hold controls sorted that particular problem.

Time to finally tackle the poor EHT regulation and the ballooning picture. Hooking up the EHT meter showed 24KV at minimum brightness, but this dropped to 19Kv at maximum brightness. The picture increased in size by over an inch and went out of focus.

As the EHT drops, the regulation circuit should compensate by increasing the HT fed to the output transistor. This proved to be increasing from 43V at min brightness to 52V at max, so the circuit seemed to be working but the EHT was still dropping.

My suspicion again turned to the tripler, so I removed it and examined it carefully. Not for the first time with this set, a schoolboy bodge was there for all to see! The casing on this tripler is clear plastic covered with clear silicon potting compound. One corner has been excavated and filled with car body filler! It looks like one of the high voltage capacitors has been removed- I guess it must have failed so I just removed it! Isopon was my 'go to' substance when I was a kid as dad always had tons of it to repair our family 1100!!

I had a spare tripler kindly sent to me by Greg (Simons) but originally from Glyn (Welsh Anorak). This had been re- sealed with brown silicon, but I had dug this out earlier in the year with the idea of rebuilding it with modern components.

So I attached some wires to it and hooked it up. It hissed a bit but worked perfectly- the EHT now only varied by about 500V over the full brightness range and the picture size was rock solid! Adjusting the focus produced a very sharp picture.

Next task then will be to decide what I'm going to insulate it with and also to dig out the body filler on the original tripler and see what's going on in there!

All the best
Nick

[greg_simons]

Hi nick
That's great news, looks like glyn did us proud with good parts, even if they were coated in the grunge of decades!, Just got to sort out that sealant.
Greg.

[Welsh Anorak]

Wish I'd kept them in a nice airtight box now!

[1100 man]

Originally Posted by greg_simons

Hi nick
That's great news, looks like Glyn did us proud with good parts, even if they were coated in the grunge of decades!, Just got to sort out that sealant.
Greg.

Hi Greg & Glyn,
It was really handy having the spare tripler to prove the point. The above successful test was done with Greg's rebuilt EHT generator board which worked perfectly.

I spent some time digging out the body filler from my tripler which took ages as it was so hard & I didn't wan't to damage the rectifier sticks.

Sure enough, the capacitor was missing! Now I want to order some new caps and replace the remaining three as they don't look too well. I am unsure what the value should be though- the manual shows them as 1000pf, but measuring the ones in Glyn's tripler shows that they are all 2300pf! I can see 12Kv on them but no capacitance value. I don't know if they have been replaced at some point as the tripler had been re- sealed.

I have no idea how critical the capacitance value is in a multiplier circuit such as this one? Can anyone shed any light on this?

I've also been considering what to use as a sealer for re- encapsulating them. Using a rigid epoxy potting compound would be easy & fairly cheap, but I would like to be able to open it up again should the need arise. So I need a flexible sealer.

Possibilities are: 1) Neutral cure silicone sealer which is cheap.
2) Polyurethane sealer (PU)
3) 2 part silicone potting compound which is at least designed
for the job but moderately expensive.

More research is needed.

Cheers
Nick

[greg_simons]

Great to see you've got a result there, I'm working on the sealant myself, silcoset 101 as used by crusty over on the other forum seems to be the ideal stuff, the manufacturers website suggests free samples may be available, I'm very tempted to give them a go, they can only say no!.
Almost at the power up stage here, all panels done and looking good, the cab repair is still causing me grief but i may have a solution.....
Greg.

[1100 man]

Hi Greg,
Whilst I'm sure the Silcoset 101 is an ideal product, I would have to rule it out due to it's high cost.

However, there are several other products available designed for the potting of waterproof, submersible electrical joints in cables. I've been investigating the range from Raytech and watching some videos on Utube.

Raytech Magic gel (NOT Wonder gel which looks horrid stuff!) is a two part potting gel supplied in two 150ml bottles. You can use as much as you need- just mix equal parts together, stir for a minute, pour into the joint and it sets in 10 mins.

It seems to end up as a tough rubber/gel - look for some video's to see what I mean, but it adheres well, is removable if needed, dielectric strength 23Kv/mm, max temp 250deg C. Looks suitable for the job and is a pleasant blue colour.

Available from Toolstation for £13.01 !! (product code 47003)

Please note: I've not tried it and am not recommending it in any way. I have no connection to either company!

However, for that price, I'll get some and give it a try and let you know what happens!

All the best
Nick

[Peter.N.]

Looks very well preserved really, obviously been kept fairly dry.

The only experience I've had anything like that was many years ago when I used to buy sets from the local tip (after proving to them I was a TV engineer) I came across one with my sticker on the back, no idea who I had sold it to.

Peter

[1100 man]

Hi Peter,
It was purely down to luck that this TV has been preserved! It could just as easily have been taken to the tip! Instead, it ended up in a dry warehouse along with a whole load of other stuff for 34 years! The cabinet is not much worse that it was when I was a kid- there isn't even any woodworm! It's really rather special to have a TV back that I last played with when I was a lad!

My object is not to do a full restoration and replace every component that might give trouble, but to achieve good functionality on both line standards retaining as many original components as possible. Callins capacitors have earned the reputation of 'replace on sight', but this set is full of them. So far only one tiny one has warranted replacement: all the rest seem to be working quite happily!

Now to the results of the 'magic gel' potting experiment! I picked up some of this stuff from Toolstation this morning (stock code 47003 £13.01).

In the pictures below, the left hand tripler is the spare one I was given, which proved to be working but needed re-insulating.

I poured out 50ml of blue 'Magic gel', and added 50ml of hardener, stirred for 30 seconds and poured it slowly into the tripler casing. It flowed very well and filled up all the spaces.

It should have cured in 5 minutes, but I had overlooked the fact that the workshop was only at 9 degrees so it took an hour and a half!

1) It's transparent with a blue tinge.
2) The consistency is that of a child's jelly.
3) It's tacky when touched.

However, when installed in the set, it works perfectly giving 24KV of EHT. There is no leakage that I can detect even when waving a screwdriver over it. I think it will be fine if it's not interfered with, but will probably end up with lots of dirt stuck to it!

So not the absolutely ideal product for the job, but ticks most of the boxes, does work from an insulation point of view and is cheap!

Having done some more research tonight, it would seem that Raytech's ' Magic rubber' would be better, but it's quite a bit more expensive at the best part of £50.

So another step forward I think. The EHT regulation is now excellent and the set is able to give a really good picture on 405- the tube seems to be in great shape giving a sharp, bright picture. If I can manage to turn the thing round with all it's innards hanging out, I'll take some pictures!

All the best
Nick

[Welsh Anorak]

It's the luck of the draw - poor Greg's TV had been kept in a damp shed without its back - not by me, I hasten to add!
The tripler's looking good - you can see the 'works' as well, which is very trendy.
You're lucky with the Callins capacitors. In my experience they change value, frequently upwards.
I'm looking forward to seeing where my basket case parts ended up.

[greg_simons]

Nice work with the tripler, as i recall in the day, before generic epoxy encapsulated triplers were common the rubber compound could be quite tacky, given a few more days it may cure a little more.
No reply from the silcoset folks yet so i will probably go down the magic rubber solution when the time comes.
Greg.

[1100 man]

After a bit of heaving & struggling, I managed to get this beast turned round on the bench so I could photograph Test card 'C' on 405. It still seems odd to hear that piercing line whistle coming from a colour set!

It's not had more than a quick rudimentary set up as yet, but for 5 minutes work roughly setting the purity, geometry, static convergence, greyscale & dynamic convergence, the results are pretty good!

Looking at the first photo, it's surprising that there is so little pincushion distortion. I can see why they didn't bother to fit correction circuitry!

The second picture shows the tuner buttons I lashed in all those years ago- the aluminium front panel has been hacked away with side cutters!

Next step is to remove the front panel and figure out how to repair it. I can then fit the nice restored tuner rather than it residing on top of the set!

All the best
nick

[greg_simons]

That really is a good picture, this was a high performance job back in the day without doubt, that front panel looks sad, is it an aluminium sheet?, i wonder if a new one could be fabricated and silk screened with the appropriate artwork, just a thought.
Greg.