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Old 19th Sep 2022, 8:07 pm   #1
THERMISTOR
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Default Ferguson 988t

Hi I wonder if anyone can help me with a problem with a Ferguson tv .I have always contented myself with restoring vintage radio sets but have come into possession of a few vintage TV sets .Never really touched them before for several reasons , the high voltages and lack of knowledge plus the possibilty of failure of the main parts , the tube and Lopt . However all being said I thought I would see what I could do . I obtained a service sheet and sorted out replacing the caps and some previous repairs . It seemed there were a few different versions of the circuit which became confusing .The Lopt coils all checked out fine on resistance readings .Finally I switched the set on . It came on with audio noise and the screen lit up with a raster . Unfortunately this lasted all of a few minutes and then disappeared , fading away . Leaving the set 10 minutes and then switching on led to a repeat .I did replace the eht rectifier but same issue still existed . Has anyone got any ideas or am I flogging a dead horse . I would be grateful for any help . Thanks Alan.
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Old 19th Sep 2022, 9:24 pm   #2
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Default Re: Ferguson 988t

Well you'll need to get a bit technical! It could be the line timebase that stops. Can you hear the line whistle when the picture fades away? Check with a meter, voltages around the line oscillator. Is the boost HT voltage OK? Basically, you are going to have to measure voltages and see what is happening. There should be a negative voltage on the control grid of the line output valve. If this is fading away due to the line oscillator stopping you will soon know as the anode of the line output valve will glow red hot.....don't leave the set on if that happens! It won't blow up or anything drastic like that but it certainly won't do the valve any good!

Don't be disheartened! It seems as though you are almost there since you do get a raster. One important point. The windings of the line transformer may have absorbed moisture over the years and this will severely damp the line stage and cause it to stop. Many restorers like to remove the transformer and leave it in an airing cupboard for a week or so, sometimes longer, to drive out any moisture. It might be worth doing the same. In the very worst cases, you may need to consider a rewind. Hopefully it will be something much simpler.

Firstly please do some voltage checks and come back with your findings.
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Old 20th Sep 2022, 3:28 pm   #3
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Default Re: Ferguson 988t

These receivers are very straightforward and reliable. Does the EY51s heater diminish when the picture fades? You need to check the CRT base voltages under fault conditions.

Pin 10 should have around 300v+, Cathode 90V and grid 0-130v varies with brightness control.

They do work very well.
Just a final note. I presume it is a 988T that you are dealing with? They are often confused with the 998T that is a completely different chassis. John.
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Old 20th Sep 2022, 6:46 pm   #4
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Default Re: Ferguson 988t

Hi all . Really grateful for the replies . I have moved on to another project I need to sort out but will get back to the Telly as soon as possible and post again . Once again thanks for the help . Cheers Alan.
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Old 20th Sep 2022, 6:57 pm   #5
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Default Re: Ferguson 988t

Just to give you a glimmer of encouragement this example was in a truly nasty state when I pulled it off the tip so long ago that I forget.
It was filthy rotten with veneer missing, chassis top rusty and the CRT surround cracked into three pieces.
It was only seconds away from being scrapped! I did the write up a while back but it turned out OK. The cabinet required veneer patches and repolishing but it works!
Good luck with yours. The LOPT tends to suffer from saturation but responds to the current through the windings trick. John.
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Old 21st Sep 2022, 7:45 am   #6
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Default Re: Ferguson 988t

https://www.vintage-radio.net/forum/...highlight=988T

That was a really super result John.

Peter
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Old 21st Sep 2022, 3:25 pm   #7
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Default Re: Ferguson 988t

Great news Alan,
Hope to see it in the not too distant future.
This is the final version of the 988T, same cabinet, chassis and model number but a larger mask opening giving the biggest picture area possible on it's dark filter MW31-74 tube.
John.
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