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Old 12th May 2022, 1:32 pm   #1
bionicmerlin
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Default Ferguson - Thorn 980

I bought this set at retrotech last Sunday. The seller did say it was working but I always buy on the assumption itís not.
Itís in excellent condition apart from a small scratch on the screen.
The seller was right it did work . I only powered it up for a few mins . The only thing I have done is replaced a Callens Cap and the mains filter cap. I think it might be prudent to replace all the blue doublers as a few are split.
It appears totally original apart from a crack on the PC board thatís been repaired.
I was lucky as I already had the service manual.
Does anyone recommend any other repairs or upgrades or just leave it at that . Andy
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Old 12th May 2022, 2:41 pm   #2
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Default Re: Ferguson - Thorn 980

Over the years, there have been several posts about this chassis and I would heartily agree with the general consensus which is to replace all the resistors and all the capacitors. Every single one of them. The problem is that this set runs very hot due to being so compact.

Mine "worked" when I first got it but the line and frame hold kept drifting the width was excessive and the frame linearity was impossible to correct. Almost every resistor had significantly changed in value, many were double their marked value, a few had reduced in value. Most of the yellow capacitors couldn't be tested because, despite using an pumped de-soldering machine, their leads fell out when they were removed. Many of the blue capacitors were already cracked. The only capacitor that didn't need replacing was the main HT reservoir and smoothing block. I also had to replace the VDR in the width circuit and some of the pre-set pots.

Having replaced everything I was rewarded with an excellent picture, one of the best performing 405 line sets in my collection but, to be fair, also the youngest. Well worth the effort of restoring.

Len
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Old 12th May 2022, 4:43 pm   #3
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Default Re: Ferguson - Thorn 980

Whilst I don't disagree with what Len has said sometimes depending on where the resistor is in the circuit, the fact that it has risen in value sometimes doesn't matter much.
The A640 I repaired recently had various faults a lot of which were down to resistors being high or open. Every resistor I checked was high or miles out. I replaced the ones causing problems but a lot of the originals remain and I bet if I tested one at random it would be out of tolerance at least.
The same with leaky capacitors sometimes it doesn't matter. Not when they are split or falling off their lead-out wires though! As yet the I.F and sound amp panel is still all on it's original parts with the exception of one electrolytic capacitor and it works fine but I bet the resistors will test high and the caps leaky.... Plus of course if it develops faults in the future I get to play with it again!
Rich
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Old 12th May 2022, 9:21 pm   #4
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Default Re: Ferguson - Thorn 980

These must have been one of the last 405 line only sets available.

I imagine many would have been used as second sets up to the switch off with only BBC2 & Channel 4 unavailable.
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Old 13th May 2022, 12:55 am   #5
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Default Re: Ferguson - Thorn 980

Len and Rich . Thanks .
I changed most of the capacitors tonight . Tested a few random resistors and only found one out of spec. What’s all the fuss about changing all these resistors. Anyway switched on and had a great picture for about 20 mins . Then what you said made sense. Frame hold needed constant adjustment every 5 mins and increase in hight.
I will get cracking with new resistors . Maybe not in the IF and sound stage for now. It might take me abit of time. Andy
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Old 13th May 2022, 8:26 am   #6
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Default Re: Ferguson - Thorn 980

Quote:
Originally Posted by Richard_FM View Post
These must have been one of the last 405 line only sets available.
I imagine many would have been used as second sets up to the switch off with only BBC2 & Channel 4 unavailable.
During the week following the 405 switch off I had around six 980's brought it for service. They all landed up in my junk shed at the shop and were passed on to 405 enthusiasts over the years. One was given to the guy that designed all the Thorn tuners and to a large part the 980 itself.

I retained a scruffy one and it still gets use as my 'workshop' TV!

These models were released in 1966 and were the last 405 line models produced. They were a good buy at 39 and a half Gns. Common fault was the line discriminator diode block and dry joints on the wire wound resistors. Cracked circuit boards were often caused by impact damage due to failure of the cabinet handle in a similar way to the KB/ITT Featherlight.

I have only had a few resistors change value but after all these years the plastic capacitors are all leaking particularly the frame stage and AGC decoupling and don't forget the little gray .01ufs. Other than the frame ones being tucked away under the tube, they are an absolute doddle to service.

Very high gain and would have been great in the fringe areas of 1950! John.
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Old 13th May 2022, 10:09 am   #7
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Default Re: Ferguson - Thorn 980

These were the very last 405 only sets to have been made. They do work well and still produce an excellent picture. I bought a second hand one back in 1971 and despite living some distance from the Caradon Hill and North Hessary Tor transmitters it gave great results on both BBC1 and ITV just using its telescopic rod aerial. It was a very high gained or sensitive set. Unfortunately it suffered water damage and was scrapped.
Some years later I was lucky enough to buy a replacement from my friend Lee. It works as new.

I think a lot of these have survived so well because they were only occasionally used as a second set as they could not get BBC2 then they were retired when the 405 line service closed
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Old 13th May 2022, 11:20 am   #8
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Default Re: Ferguson - Thorn 980

Weren't some of these given away when you bought a new Thorn 2000 colour set in the late 1960's?
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Old 14th May 2022, 1:17 am   #9
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Default Re: Ferguson - Thorn 980

All great information thanks.
Can I ask is this the diode block that has been mentioned and already replaced. It looks like a transistor. Part number
MSDD 7002 I think.
Should I leave it or replace with new diodes . Andy
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Old 14th May 2022, 8:09 am   #10
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Default Re: Ferguson - Thorn 980

That diode 'block' looks OK. It is the later type. The earlier one was larger and square. Both can be replaced with 1N4148 type diodes, they are not critical. The rear line and frame hold controls are often the cause of intermittent loss of line and frame hold. Cleaning does not help.

The 980 was included as a 'free' package when you rented a Thorn 2000 from DER [not Derwent]. John.
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Old 14th May 2022, 9:52 am   #11
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Default Re: Ferguson - Thorn 980

Quote:
Originally Posted by Heatercathodeshort View Post
The 980 was included as a 'free' package when you rented a Thorn 2000 from DER [not Derwent]. John.
Here is a DER 405 only portable from 1969...
https://www.radios-tv.co.uk/communit...-tvs/der-5649/
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Old 14th May 2022, 6:47 pm   #12
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Default Re: Ferguson - Thorn 980

Andrew . Thanks for the link . Wouldnít mind one of those sets myself.
John thanks for the info thatís great.
I suppose itís a good idea to change those pots then .
I have looked in my bits and pieces and donít have anything new.
Can anyone recommend sensible replacements. And where to get them . Andy
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Old 14th May 2022, 8:00 pm   #13
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Default Re: Ferguson - Thorn 980

If you need to replace the pots then go for Piher PT15 with the extensions, just the job. I got mine from Cricklewood Electronics.

John.

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Old 14th May 2022, 11:54 pm   #14
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Default Re: Ferguson - Thorn 980

John . Thanks for that . It looks a proper job. I will put them on my shopping list
Andy
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Old Yesterday, 7:45 am   #15
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Default Re: Ferguson - Thorn 980

The 16" version of the 980 was quite rare over 40 years ago. J.
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Old Yesterday, 8:11 am   #16
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Default Re: Ferguson - Thorn 980

The symptoms of a dried out C36 1uf electrolytic are incorrect line speed, one ended line hold control and line jitter.
Just replace it! J.
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Old Yesterday, 12:34 pm   #17
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Default Re: Ferguson - Thorn 980

Thanks John I did replace that already. It was a Callins. I have replaced all the caps apart from 2 . They are on my shopping list.
Incidentally I did test all the old ones and they tested ok even the split ones.
I do remember what you have said in the past capacitors often test ok but are still suspect so I normally apply that rule.. Andy
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Old Yesterday, 2:33 pm   #18
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Default Re: Ferguson - Thorn 980

They may be ok when cold but will be very leaky as they warm up causing the frame to creep up from the bottom and uncontrollable AGC, the symptoms of which are signal overload with the contrast control having very little effect.. Looks a good! John.
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