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Old 8th Jun 2019, 12:14 pm   #41
Welsh Anorak
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Default Re: My Thorn 2000 back after 34 years!

Sorry about the state of that tuner! It was just lying in the bottom of a long-forgotten box of Thorn bits that didn't get thrown out more by luck than judgement. Of course when sets like this were scrapped no-one could have imagined they would be desirable so many years in the future. If only we'd had a crystal ball....
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Old 8th Jun 2019, 1:13 pm   #42
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Default Re: My Thorn 2000 back after 34 years!

Indeed Glyn
I wince at the thought of all those early CTV's we broke up at work when they were clapped out from a long rental stint, never gave a thought to whether they would be collectors items, they were plentiful and cheap and most were ragged for spares, should really have kept an example of two.
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Old 10th Jun 2019, 10:23 pm   #43
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Default Re: My Thorn 2000 back after 34 years!

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Originally Posted by Welsh Anorak View Post
Sorry about the state of that tuner! It was just lying in the bottom of a long-forgotten box of Thorn bits that didn't get thrown out more by luck than judgement.
Apart from the heavy rust and filth, it's actually survived surprisingly well! On removing the rusty lid, I was amazed to see the internals were corrosion free and only a little grubby. The band 1, band 3 & UHF slide switch was also in good order and all the electronics look unharmed.

The tuner body was originally plated with a silvery zinc. The top cover, front bracket & band selector slide bar were all gold passivated. As the body couldn't be re-plated anyway due to the electronics and we didn't have enough stuff for a batch to go to the platers for the gold parts, painting was the only option.

This technique, (activated 2 pack base coat matched to the colour) worked well on my Pilot chassis. Obviously you can't match gold passivate with paint, as it contains multiple shades, but my friend Jon came up with something that looked pretty good.

The tuner body was carefully masked to prevent sand getting where it shouldn't, and then all the parts gently sandblasted with fine grit.

After being treated with a rust killing fluid and a final clean, all the bits were sprayed with their respective colours.

After overhauling/ de-rusting the button unit & cleaning up the wiring & switches, it was all put back together.

I'm pleased with the end result, but as yet, I've no idea if the electronics work!

The biggest problem is the lack of useable tuner buttons. Whilst all six buttons were present, the plastic has crumbled away where they mount to the shafts. The buttons only allow the shaft to be rotated when pulled out, which makes them difficult to repair.

So if anyone has any spare buttons....

All the best
Nick
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Old 10th Jun 2019, 11:07 pm   #44
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Default Re: My Thorn 2000 back after 34 years!

Hi nick
Good work on the tuner, I hope it works as good as it looks, I'll take a look in the spare buttons bag tomorrow but don't hold your breath, I'll get the 2 k spares done as well, I'm pleased with the system switch, all contacts work fine.
Might be worth a general ask on the wanted thread for the buttons, they must surely be common to other models of the period.
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Old 12th Jun 2019, 10:57 pm   #45
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Default Re: My Thorn 2000 back after 34 years!

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Originally Posted by Welsh Anorak View Post
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.
Having now studied how the tuner operates, I see exactly what you mean.
Each button can be arranged to be either band 1 405, band 3 405 or UHF. To set each button required a visit by an engineer as the tuner has to be removed to make the adjustments!

The 405/625 changeover microswitch is operated by a bar that runs past all 6 button spindles. To make a button 625, the knob has to be removed and a spring, washer & circlip added to the shaft. This then presses on the bar when the button is pressed in.

The problem is, as soon as the button un- latches, the system switch changes back to 405. So if you're on 625 and then select another 625 channel, the set momentarily changes over to 405 and then back to 625! Madness!!

When there was only one 625 channel, I suppose it was not a problem, but once multiple 625 buttons were in use it must have been a nightmare of burnt system switches and dead line o/p transistors!

I connected up my newly refurbished tuner and unsurprisingly, it didn't do anything: not a sausage! I didn't really expect that it would considering the state it was in. So time to do some fault finding with the scope and signal generator and find out what's going on.

Cheers
Nick
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Old 13th Jun 2019, 11:48 am   #46
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Default Re: My Thorn 2000 back after 34 years!

The accepted simple cure was to open the three spring resistors on the reverse of the power board. Of course this could be too late...
I can't believe that's 'my' tuner! It would have been OK before it had a long rest, but that means very little of course. Mind you, I have no doubt it will soon be up and running again.
Unfortunately, the only tuner I can think of with similar knobs was the rare 6-button 950 set, and possibly early 1400s - the 17" one with the buttons under the CRT. Of course they'd only have four buttons. It might be possible to mate later buttons as used in the 1500s with your knobs if the spindles are the same diameter. Not easy, though!
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Old 13th Jun 2019, 7:00 pm   #47
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Default Re: My Thorn 2000 back after 34 years!

Dear Nick,

Congratulations on being reunited with your 2000. The 2000 was the first colour TV that I repaired (line output transistors) while an apprentice and the first colour TV that the shop stocked. Hence my forum name.

Some years ago I had to leave my business premises (several robberies and subsequent loss of insurance cover) and most of my collection of interesting television sets had to go but I kept a 19" 2000, one of only two that I had repaired over many years, hopefully I will restore it one day.
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Old 13th Jun 2019, 9:02 pm   #48
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Default Re: My Thorn 2000 back after 34 years!

Indeed Glyn. The earlier Thorn p/b tuners used 1/8" spindles where later ones used 1/4".
I remember fitting a new UHF tuner to a 1400 when the original developed intermittent loss of signals.
Although it was a direct plug in replacement, I didn't expect to have to fit new buttons as well. Cured the fault though.
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Old 13th Jun 2019, 10:47 pm   #49
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Default Re: My Thorn 2000 back after 34 years!

Hi Nick,

I have been reading here and following the progress of this repair. Very nice and interesting set. It's great to see that you have brought it back to life again.

Would a 3D printer be an option to make replacement tuner buttons? I think any button from that era would probably be very brittle and would not withstand normal use for very long.

I had this problem on one of my Sony TV9-90UB sets. The fine tuning dial had fallen to pieces. I took the broken dial to a friend who has a 3D printer and he made a new dial for me that worked perfectly and looks almost like the original. Depending on the shape of the buttons and the forces they need to handle 3D printing might be an alternative for creating new buttons. Just an idea...


Cheers

Semir
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Old 13th Jun 2019, 11:31 pm   #50
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Default Re: My Thorn 2000 back after 34 years!

Hi Semir,
I guess 3D printing might be possible, but that's well outside my skill set! What makes these knobs more tricky to replicate or modify from another set, is that they comprise two parts with a spring inside which are solvent welded together.

Normally, the knob rotates freely without engaging with the spindle. The knob is pulled outwards to engage the spindle for tuning.

I checked my 1400 tuner and while it does have 1/8" spindles, the knobs are single piece. The 1500 tuners I have, have 1/4" spindles.

I will put up a request for some buttons, but I imagine they will be scarce. I think two of mine are useable, one is engaged all the time, and three have broken centres. If none are forthcoming, I'll have to try and reconstruct the ones I've got!

All the best
Nick

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Old 13th Jun 2019, 11:42 pm   #51
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Default Re: My Thorn 2000 back after 34 years!

Hi Geoffrey,
Thanks for your comments. Nice to know you still have a 2000. Maybe the two current threads will inspire you to dust off your one and start the restoration!

Cheers
Nick
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Old 21st Jun 2019, 11:47 pm   #52
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Default Re: My Thorn 2000 back after 34 years!

To facilitate repairing the tuner, I decided to hook it up to a known working dual standard TV and get it working on Band 1 first. My reasoning being the frequencies are lower and within the capabilities of my 'scope & sig gen.

Connection was straight forward as it only needs a 30V supply and the AGC line already has a fixed bias.

Connecting up the Hedgehog on Ch1 produced a perfectly good picture. One of the many things I love about the HH is the knob on the front to change channel. This allowed me to easily check the tuner over the whole Band 1 range.

Setting the tuner to Band 3 and adjusting the HH accordingly, proved that it worked fine on this band as well.

Selecting UHF and changing the TV to 625, showed the tuner to be working fine, so the next move is to connect it back up to the 2000 and find out why it wasn't giving any pictures.


Ultimately, I would like to have 3 buttons on the tuner for UHF, two for Band 1 405 and one for Band 3. I don't like the idea that every time a different UHF channel is selected, the set changes momentarily to 405 and then back again. That seems a sure way to kill the line o/p transistors! I am trying to devise a way to prevent this, but the mechanics of the tuner don't lend themselves to do it. More thought needed on this one!

And now to the broken tuner buttons. Semir wondered whether the buttons could be 3D printed and in fact a kind forum member with a 3D printer said he might be able to help.

Each button consists of three plastic parts and a spring. I've dissected all 6 buttons and the outer parts can all be re-used. It's the inner part the fits on the tuner shaft that needs re making.

This looks to me to be a rather intricate part to print as it has fine detail in the form of little gear teeth and the whole thing is pretty small. It might be possible though but I will see if anyone can find some spare buttons first.

Actually the shafts on the tuner measure 3/16" rather then 1/8".

All the best
Nick
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Old 22nd Jun 2019, 12:32 am   #53
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Default Re: My Thorn 2000 back after 34 years!

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Ultimately, I would like to have 3 buttons on the tuner for UHF, two for Band 1 405 and one for Band 3. I don't like the idea that every time a different UHF channel is selected, the set changes momentarily to 405 and then back again. That seems a sure way to kill the line o/p transistors! I am trying to devise a way to prevent this, but the mechanics of the tuner don't lend themselves to do it. More thought needed on this one!
It's easy. Just swap over the NO and NC connections on the micro switch. Then on the buttons you fit springs for 405 and leave them off for 625.

It does mean though though that if you change from one 405 channel to another the set momentarily switches to 625, but I imagine this is less commonly done. I did this many years ago when I had a 2000 as my only colour set.
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Old 22nd Jun 2019, 1:14 pm   #54
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Default Re: My Thorn 2000 back after 34 years!

This switching is not a good thing, and led to the demise of many a 2000 as we've discussed earlier. However I'm sure Mikey 405 devised a mod to prevent this happening, renderng it more conventional, though I'm sure you could work out a way.
Told you it was a good tuner - only needed dusting!!
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Old 22nd Jun 2019, 1:22 pm   #55
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Default Re: My Thorn 2000 back after 34 years!

How about disconnecting the micro switch entirely and fitting a small 405/625 switch on the back panel independent of the tuner.
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Old 22nd Jun 2019, 4:02 pm   #56
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Default Re: My Thorn 2000 back after 34 years!

Hi nick, glad to see the tuner's ok, the buttons are tricky but the parts look as though they would lend themselves to 3d printing, as Glyn says it just needed dusting down!, Looks like you're nearly there with yours, mine is progressing nicely, last few parts to fit and then get the mainframe up for cleaning, the carpenter comes on Friday for a look at the cab, I'll let you know how it goes!.
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Old 23rd Jun 2019, 11:44 am   #57
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Default Re: My Thorn 2000 back after 34 years!

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How about disconnecting the micro switch entirely and fitting a small 405/625 switch on the back panel independent of the tuner.
That's probably what I will do, at least until I've finished all the testing & repairs.

I could replace the front panel 'tint' control with a rotary 405/625 switch. Once the greyscale is set up, the tint control probably won't be needed and the mod could easily be reversed.

What it needs is a mechanical delay fitted to the microswitch operating mechanism on the tuner. Something like those dampers used on cassette deck doors. That would keep the thing in 625 while the next 625 button is pressed.

I've thought about doing it electronically, but then you have the problem of a change of state at switch on. I'll need to give it more thought, but it's not a major problem to deal with yet!

I would be interested to know what Mikey 405 did to get over the problem?

All the best
Nick
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Old 23rd Jun 2019, 11:56 am   #58
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Default Re: My Thorn 2000 back after 34 years!

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Looks like you're nearly there with yours, mine is progressing nicely, last few parts to fit and then get the mainframe up for cleaning, the carpenter comes on Friday for a look at the cab, I'll let you know how it goes!.
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
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Old 23rd Jun 2019, 1:40 pm   #59
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Default Re: My Thorn 2000 back after 34 years!

With reference to Greg's post, we binned loads of G6's and 2000's. Even in the 80's if a 3000 (Thorn) came in we shuddered because they were considered junk. Now we feel spoilt if we see one, but a 2000! I'd kill for one. We used to neck them. When I came into the trade (1970?) I was given a 2000 to play with at lunchtimes. Being new to the trade I gained many hours of pleasure.
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Old 23rd Jun 2019, 1:47 pm   #60
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Default Re: My Thorn 2000 back after 34 years!

At DER Ltd in the 70,s,I did my training (colour) on the 3000 but still of course had to repair to component level the 2000,s.

Not difficult once you understood them.
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