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Old 19th Aug 2005, 8:45 am   #1
David_Robinson
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Default Thorn 980 Faults

[Continued from Last All Valve / Hybrid Set

[Re : Thorn 980]

Quote:
Originally Posted by Heatercathodeshort
The only faults were poor line sync diodes...
John, that's an interesting point because my set suffers from line oscillator drift with the line hold having to be reset after about half an hour. Is that likely to be the diodes do you think, or is it worthwhile replacing the slightly obscure 6/30L2 (ECC804) oscillator valve?
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Old 19th Aug 2005, 6:44 pm   #2
Heatercathodeshort
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Default Hybrid TV Faults

Hello David,
The 6/30L2 valve is a very rare failure. I know I have said this about valves before but I would estimate that over 50% of valves replaced for faults were not in fact responsible for the fault! The line sync diodes on the 980 were a stock fault. The original diodes were enclosed in a common pack and failed within 12 months. They can be replaced by a pair of silicon diodes such as the 1N4001. The exact type is not critical. You may well have the original pack in our set. If this fails, suggest you thread. We may have shift this to another topic section. Regards JOHN.
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Old 21st Aug 2005, 8:36 am   #3
David_Robinson
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Default Re: Hybrid TV Faults

Thanks John, some new diodes have indeed 'rectified' the problem! The original device looks like a transistor and seems to read OK on a meter, but now the line lock is a lot more solid. The pincushion distortion and line linearity are still pretty dire, but I guess these are 'not faults, but features'.

I agree with your comments about valve replacement - people are too ready to swap valves because it's easy to do. I haven't replaced any valves in this set. Most valve failures in my experience are due to external faults that overrun the valve, such as leaky grid coupling capacitors or cathode bias resistors going low.
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Old 21st Aug 2005, 7:22 pm   #4
Heatercathodeshort
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Default Re: Hybrid TV Faults

Hi David,
Well thats part of it solved! The pincushion fault can be cured by bending the 'T' shaped ears that are mounted on brass strips from the deflection coils. As to the line lin problem, you may find that the 'closed loop' sleeve mounted or rather slipped between the scan coils and the crt neck has been pushed too far in the coil assembly. Suggest it has about 1/4" of space between the plastic ring [if its still there..] and the scan coil clamp ring. The picture should be of good geometry on this sets. Good luck with it! Regards JOHN. PS You did have the original diode pack by the way.
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Old 22nd Aug 2005, 10:49 am   #5
David_Robinson
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Default Re: Hybrid TV Faults

Thanks John, yes I know about the pincushion magnets, but those for E-W are not quite strong enough no matter how you adjust them, and as for N-S - there aren't any! Maybe I'm being too fussy. The results aren't too bad.

http://homepage.ntlworld.com/david.r...20geometry.JPG

This picture is best viewed at 100% - there is a lot of aliasing on the camera with the TV line structure, so any attempt to resize it creates a bit of a mess!

I have readjusted the line linearity sleeve - it actually needed to be further in.

Thanks
David
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