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Old 2nd Jan 2016, 5:27 pm   #1
GadgetM
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Default Problem with Granadacolour C20TA5/GEC

Hi, after having some great help with this set previously I'm hoping someone can help me locate and repair another fault.
It's a granada from 1978/79, and a rebadged GEC.
The screen suddenly went almost totally white, with flyback lines all across the screen. I've checked and swapped out every board in the set except the board with the line-output-transformer / "horizontal" controls, the only board I don't have a spare of.
I've checked for blown resistors and shorted caps but all seems fine as far as I can see.
Does anyone here have any experience with these or happen to have any old spare boards?
Any help or advice greatly received, as it's such a nice set (had a stunning picture) I'd hate to retire it. Thanks
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Old 2nd Jan 2016, 6:04 pm   #2
MALC SCOTT
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Default Re: Problem with Granadacolour C20TA5/GEC

Sounds like the 200v supply to the RGB output transistors is missing. This will be fed from the loptx via a safety resistor and diode. The smoothing cap could also be o/c on this supply, Malc.
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Old 2nd Jan 2016, 6:09 pm   #3
John123
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Default Re: Problem with Granadacolour C20TA5/GEC

Probably something like a bad boost capacitor on that LOPT board. If you have access to an ESR meter you could test them, but with a set of this age it's probably just best to go ahead and blanket replace (the critical ones).
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Old 3rd Jan 2016, 11:36 am   #4
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Default Re: Problem with Granadacolour C20TA5/GEC

Thanks Malc and John, but I'm a bit out of my depth here. Sure there's no voltage at all reaching the transistor (large one mounted to heat sink), but I've been unable to find the cause. Can't find any dead diodes, resistors or shorted caps. Any idea what pin of the lopt supplies that voltage?
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Old 3rd Jan 2016, 3:13 pm   #5
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Default Re: Problem with Granadacolour C20TA5/GEC

My mistake.... sorry, there is 400v at the C of the transistor, no voltage at B or E.
The C appears to be fed from the 1200v pin of the LOPT, but that in it's self is putting out just 400v. Any suggestions?
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Old 4th Jan 2016, 12:50 pm   #6
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Default Re: Problem with Granadacolour C20TA5/GEC

There should not be anywhere near 400v on the collectors of the rgb o/p transistors. Do you have a cct diag you can post? Malc.
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Old 4th Jan 2016, 4:32 pm   #7
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Default Re: Problem with Granadacolour C20TA5/GEC

Hi, I have no service data at all I'm afraid. The board with the R, G and B controls and transistors isn't the problem (vertically mounted board on left), I have a good spare board from another set (with duff tube), which when inserted does exactly the same thing, I also swapped the tube base board and power supply board, the only board that remains is the lopt board, which I don't have a spare of, so by process of eliminating all other boards, this is the only one left. The transistor I was referring to here is the one on the headsink at the rear of the lopt board, fed from the lopt, the pin labelled 1200v on the lopt is down to just 400v feeding the collector of that transistor.
I think given my total lack of service data, a board swap is the best option, but who has spares of those these days?
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Old 4th Jan 2016, 5:21 pm   #8
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Default Re: Problem with Granadacolour C20TA5/GEC

Plenty of spares if you are talking reses and capacitors.The feed off the loptx to video output transistors (RGB) is around 180 to 200 Volts when correct.

The feed comes off the transformer (loptx) via a safety resistor and a diode then the 400 Volt cap.

The diode and or the res will be at fault plus the cap can cause your symptoms.It should be a quick fix.

The transistor on the heatsink from what you say is the line output transistor.
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Old 4th Jan 2016, 10:19 pm   #9
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Default Re: Problem with Granadacolour C20TA5/GEC

Thanks to malc, John, hamishboxer,. I replaced the diode and 47uf capacitor on the 185v feed from the lopt to the rgb transistors, and Viola! A picture. The colours just need a bit of adjusting now then done (well, until the next time..... it is very old after all).
Photo attached shows the now repaired set next to my stand-in set, a ferguson tx100, which is actually pretty good.
Cheers!
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Old 4th Jan 2016, 10:25 pm   #10
McMurdo
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Default Re: Problem with Granadacolour C20TA5/GEC

dont set the framing with that widescreen test card will you!!!

Looks a nice pic
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Old 4th Jan 2016, 11:09 pm   #11
GadgetM
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Default Re: Problem with Granadacolour C20TA5/GEC

No, the framing's already fine, I have a DVD of proper 4:3 testcards for any adjustments, I did use that to tweak the convergence though.
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Old 5th Jan 2016, 1:35 am   #12
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Default Re: Problem with Granadacolour C20TA5/GEC

Nice one, well done!
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