My Thorn 2000 back after 34 years!

[Electricdreams]

I love the look of this TV!

Very Stylish!

[Richard_FM]

Originally Posted by greg_simons

Guilty as charged I'm afraid, I've rekindled your interest in the mighty beast, there's no letting go now!.
Yes indeed, the sheer amount of stuff in there is staggering for a domestic TV, some of which parts were being pressed to the limits of their specification, many thank for those pics, they told me what I needed to know, best of luck with yours.
Greg.

It's unsurprising that Thorn lost money on every set made.

[Welsh Anorak]

Welsh mud indeed! That's very high quality hydrated sand and humus, I'll have you know...

[1100 man]

Well whatever it is, there was a goodly quantity of it in the bottom of the box Greg sent me the tuner in! Made me smile when I unpacked it!

Seriously though, I'm well pleased to have finally got one and it will be great after a strip down and some TLC. Thanks to both of you for making that happen!


Having lugged it onto the bench the other night, I 'set to' this evening and gave it a good look over, partly to see what hideous things I'd done to it in the past, and partly to decide how I was going to tackle it.

The general condition of the chassis & PCB's is excellent- looks like it's been kept pretty dry with very little dust.

My handiwork is as follows:

1) Throw original tuner away and fit an electronic one (from a Pye CT205 I think). Mount tuner on nail banged into the inside of cabinet

2) Fit button unit from CT205 by hacking away the front panel where the original buttons were Well the hole spacing was different!

3) VT2 on power board hanging in free space and has obviously come off a scrap pcb as it's got wires extending it's legs!

4) 68V Zener diode replaced with something too small so has a bit of aluminium wrapped round it bolted to the chassis to stop it overheating!

5) Throw internals from system change solenoid on line scan board away as we'll never use 405 again will we?

There's a few track repairs on several boards, but most components look original.

My conclusion is that there are an awful lot of electrolytics in there and most of them are the dreaded Callins ones. However, I don't believe they are all faulty- after all, I'm the same age as they are and I still work quite well so I don't see why they wont! So I'm not going to blanket change them, but will have the fun of actually diagnosing and fixing faults as they appear.

I decided to disconnect the power feeds to the line scan & EHT boards and then apply some mains via a variac, gradually increasing the voltage over an hour or so and monitoring the various supplies.

The end result of all that was at full mains voltage, the power supply & regulator boards were working fine and all the supply rails measured what they should. There was a good hiss from the speaker and the frame stage could be heard gently purring away.

On connecting up the RF output of a VCR and a quick twiddle of the tuner buttons, Nirvana came blasting out the speaker!

Looking at the luminance output of the IF board, showed that video was present but not looking too good. There was some pretty grim video present at the blue cathode of the tube but I wasn't expecting much at all at this early stage.

So a very good start I think. The next step will be to see if the line scan and EHT generators can be made to function and then whether the tripler is any good.

Cheers
Nick

[thermionic]

Good luck with this, Nick. An exciting project and a trip down memory lane.


I’ve always liked this picture of the 2000 Chassis under development at Enfield. It’s amazing to think that the designers, John Bussell and Sid Jones, managed to achieve what they did given the state of that workbench!


Picture taken from the book, ‘The Setmakers’


Cheers. SimonT.

[Andrew2]

I've got that book, Simon. It's a great read, especially the chapters concerning the 405/625 era and the development of colour. That photo always amuses me, as does the section regarding the development of the solid-state LOP/EHT section (was it the 2000 or 3000?) when they slowly filled up a large coffee jar with popped transistors, which were expensive radar switching devices.

[1100 man]

Having got some sensible voltage rails coming from the power supply & regulator boards, the next step was to power the line scan & EHT boards.

I pondered whether there was a less potentially destructive way of doing this, but concluded there probably wasn't, so adopted the 'what's the worst that can happen' approach!

There was once a time where I could easily hear a 625 line stage in operation, but sadly those days are long gone However, the 850V A1 supply is derived from the line output transformers, so by monitoring that I could tell if it the line stage was working. I was planning to leave the EHT generator disconnected for the time being.

Switching on, after a second or so, the 850V rail rose to about 800V with no drama, smoke or fire! So the line stage must be functional.

Nothing to loose now, so I connected up the EHT generator and switched on again. I was rewarded with that old familiar 'rustle' of EHT on the screen and low and behold, a raster!

Applying a signal from a VCR, a not un-respectable picture was produced after a little careful twiddling.

Considering this set has not been powered for 30 odd years and stored in an unheated warehouse, the pictures are surprising. Don't forget also, that so far, not a single component has been replaced and there is a veritable forest of Callins electrolytics in there!

Even the tripler works, at least for now and the convergence is pretty good too!

Mind you, from here on in, the long slog of achieving optimum performance and reliability begins!

So who can name the music video and the satellite channel it was recorded from in the '90's? Proper analogue satellite too, complete with comet tails in areas of high saturation!

Cheers
Nick.

[Clydeuk]

The channel looks like the German? Viva music channel. I used to pick this up from Eutelsat 13 east in the 90's. No idea what the video is.

[Philips210]

Hi Nick.

That's coming along well. The CRT looks reasonable with good focus. The 2000 is a great restoration project.

Regards,
Symon.

[greg_simons]

Hi nick
Well done, it's alive without any drama, now you've got all those nasty caps to replace!.
My own 2000 is coming along nicely, only a couple of panels left to do plus a long checking and re-checking process, langrex are being kept busy with small orders for devices etc and a few eBay suppliers.
Still pondering that wreaked cabinet,,,,,
Greg.

[1100 man]

Originally Posted by greg_simons

now you've got all those nasty caps to replace!.

Those lovely Callins caps are as old as I am, so unless they prove themselves to be faulty; they're staying put!

Tonight, though, the first one has admitted it's guilt! This evening's task was to find out why there was no colour. Adjusting the reference oscillator frequency did produce some very weak, unstable colour. The saturation control had no effect. Measuring the voltages around the first chrominance amp (VT13), showed that it was biased fully off.

This implied that the colour killer was operating which meant there was a problem with the burst gate or associated circuitry. A quick check around VT1, the burst gate transistor, showed there was no volts on the collector. The culprit was C3, A 4mfd Callins which was dead short!

Removing it restored plenty of solid colour which actually looks really good- no Hanover blinds or other problems!

Hi Greg,
Glad you are making progress with yours. To be honest, I really didn't think my one would come back to life with so little effort after so long! Your's is somewhat more of a challenge (and therefore much more fun!). I don't see that you have any option but to reconstruct the cabinet- time to dust off those woodworking skills you learnt at school

That's coming along well. The CRT looks reasonable with good focus. The 2000 is a great restoration project.

Thanks, Symon. I always remember that the set produced very good pictures and so I never had any reason to expect that the CRT would be low emission.

Luckily the 2000 is fairly basic from a circuit design point of view. There is an awful lot of it, and it's all discrete, but there are no outlandish design ideas like the Syclops power supply/ line stage of the 9000, so faultfinding should be fairly straightforward.

The channel looks like the German? Viva music channel. I used to pick this up from Eutelsat 13 east in the 90's.

Well done Clydeuk, It is indeed Viva One from Eutelsat. That was the golden age of free satellite music channels. 13 east had several good German, French & Polish channels. I had two LNB's on my dish slightly offset so I could receive both Astra & Eutelsat.

All the best
Nick

[1100 man]

Back in 1983, when as a very pimply youth, I was trying to turn this into a usable TV, 405 line was totally obsolete. To my knowledge, I never tried to get it working on 405- why would I?

I must have had problems with the original tuner, so that got thrown away and a UHF only one lashed in place - hung on a nail banged into the inside of the cabinet!

The system change switch on the line timebase had been disabled by removing the internal metal plunger from the solenoid. Also it's feed resistor on the power board had been removed.

Not having been able to locate another metal plunger, i decided to make an exact copy of the one in the solenoid on the convergence board.

The original plunger measures 8.9mm diameter, a rather odd size. Not a problem with a lathe, of course, but I don't have that luxury! The nearest I could find was 9.2mm from the shank of an imperial sized bolt.

Using some rather crude techniques, I reduced this to the correct size. The small right angled rod connected to it was taken from a bicycle wheel spoke! How's that for recycling!

I was quite pleased with the end result- the original part is the upper one and my copy is the lower.

However, careful examination of the system switch on the line scan board shows it was disabled for good reason- there are burnt contacts and all is not well.

So the next task is to remove it from the board and see if it can be repaired.

All the best
Nick

[dtvmcdonald]

Originally Posted by thermionic

Good luck with this, Nick. An exciting project and a trip down memory lane.

... state of that workbench! ...

Picture taken from the book, ‘The Setmakers’

Oh please! "state of that workbench". That's how REAL designers pre digital worked.

An any case, they had the very finest technology of the day applied, as
clearly seen along most of the left edge of the picture.

[1100 man]

A serious session with the soldering iron and solder sucker, and the system switch was removed from the board.

There is a set of contacts that operates as 'break- before- make' which removes power to the line output stage as the system switch operates. I can't believe the LOP stage appreciates a removal of it's supply for just a few milliseconds!

Not only does this set of contacts carry the full LOP supply current, but to achieve the 'break before make', the contacts are only half the width of the normal ones.

Unsurprisingly, this set of contacts were just a charred mess and had been linked out on the PCB.

I imagine this part of the system switch was probably the most unreliable part of the whole set. It's a very poor design.

Looking at the circuit diagram showed, rather bizarrely, that the next set of contacts along on the switch was unused.

These were standard sized and needed to be modified with a Dremmel and miniature file to become the 'half sized' contacts of the original switch.

How well all this will work remains to be seen, especially as the modified contacts are just plain brass on the ends rather than silver plate.

The solenoid which operates the switch, for which I made the new plunger, comprises of two coils wound on a moulded plastic former. The end where the plunger goes in had fractured, breaking one of the connecting wires. I had to glue this back together and perform some micro - surgery to re attach the wire to the coil.
Luckily, the whole coil assembly is symmetrical, so I could reverse the whole thing, allowing the plunger to operate in the undamaged part.

So now it's a case of putting it all back together and seeing how well it works!

All the best
Nick

[greg_simons]

Hi nick
That's some progress, before you go filing away at the line switch I have the remains of a spare, the bottom fixed blades are fine, just the one slide contact wiper is damaged, with some micro surgery it can be replaced with the adjacent good one that's unused, I think when the set was designed and tested it probably worked fine with engineers changing channel, put it in the customers home. different story, probably gave up the ghost rapidly with the owner banging away at the buttons trying to find Wimbledon etc.
Also I have a slightly better PSU panel, only a couple of track joins!, needs complete restoration, no 80 ohm fusibles unfortunately.
Look forward to seeing the before and after pics of that tuner unit when it's done.
Greg.

[Welsh Anorak]

The problem was that the system switch would clunk in and out madly on channel change, even when the set was set for 625 lines unless the three PSU resistors were opened.
I believe the break before make contact design was done deliberately as the line output transistors used to fail if this wasn't the case. Why, and how this was better, I can't imagine, but it did seem to work, at least for as long as dual standard operation was required. I assume Thorn (correctly in most cases) assumed most would have the dual standard option removed early in the set's life.

[vidjoman]

When first introduced the main stations were all 405, and only BBC2 with limited appeal was 625 in colour. Some people watched it just because it was colour.

[HamishBoxer]

The first or one the first programmes was Wimbledon.Of course all the renters used to wind up the colour to bright green or they were not happy!

[1100 man]

Originally Posted by vidjoman

When first introduced the main stations were all 405, and only BBC2 with limited appeal was 625 in colour. Some people watched it just because it was colour.

Presumably, though, if you had gone to the huge expense of buying or renting one of these beasts, you must have had a serious desire to watch BBC2? So I would have thought it was highly likely that these sets would be used on both line standards.

I would imagine that some areas took quite a while to get the other two channels on UHF, thus prolonging the need for dual standard use.

I believe the break before make contact design was done deliberately as the line output transistors used to fail if this wasn't the case. Why, and how this was better, I can't imagine, but it did seem to work, at least for as long as dual standard operation was required.

Yes it seems strange as the interruption of power would only have been a few milliseconds. You would think that would do the LOP transistors more harm than good!

My set seems to have it's original transistors- they are both identical Texas Instruments branded ones. I certainly would not have changed them as a lad as I would not have had access to new ones- I only had spare valves!

It remains to be seen how long my modified switch lasts- I'm planning to use this as a DS set so it will need to work! It's soldered back into the board now, but Greg has kindly offered to send me a less damaged switch.

I've also been directing my attention towards the multi band tuner unit given to me by Greg but originally coming from Glyn (Welsh Anorak).

This is a 6 button mechanical tuner capable of receiving band 1, band 3 and UHF. Whilst it is very rusty and filthy, I was really pleased to get hold of it. The rebuild is going well & I should have some pictures soon.

Meanwhile, this is what it looked like...

Cheers
Nick

[Richard_FM]

Originally Posted by HamishBoxer

The first or one the first programmes was Wimbledon.Of course all the renters used to wind up the colour to bright green or they were not happy!

My Dad's first remembers seeing colour TV was a set in a shop window showing Wimbledon, with the colour turned so their bottles of Robinson's squash looked like it was glowing orange.