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Old 29th Dec 2006, 3:20 pm   #1
Dr-Watts
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Default GEC 2028 restoration - advice with sync fault

Hi All,

What a great site !
I'm in TV Anorak Heaven

I'm currently restoring a GEC 2028, it had sat around for many years and it is still in 'showroom' condition. (I'm sure I paid far too much for it though!)
There were some interesting faults, first it was dead (no HT); this turned out to be a track that had passed away (on the dropper board on the right).

Then, when it did rustle up there was no width at all! This turned out to be the 'S-correction cap' The nice yellow chap was S/C, and now...

Very, very, weak sync. I have replaced the obvious valves and found that D501 was as leaky as hell, (funny square black thing with 3 legs and 2 diodes in it). I just can't seem to find one for love or money so I have replaced it with 2 1N4007's, will this work ?

You can get it to sometimes lock by de-tuning it and then slowly re-tuning it to your desired station.
I have also cleaned all sections of the system switch and it all seems OK.
When the picture does lock (very rarely) it's remarkably good, the tube doesn't seem to have seen much use!

I must also add that the red 'colour beacon' does work
If anyone's got any tips, please get in touch. Likewise, the tripler could do with replacing, has anyone got one for sale ?

I never had this much trouble restoring my superb 74 Decca Bradford ! ! !
The Bradford gets used every night, and apart from the annual frame fault (every Xmas) it always gives excellent results.
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Old 29th Dec 2006, 5:00 pm   #2
Steve_P
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Default Re: GEC 2028 Restoration - Advice with Sync Fault

Another one! Welcome aboard, sir!!

Is it frame, line or both syncs that are dodgy?
The sync amplifier on these is a PCF80, which I take it you've changed. The syncs come off the PCF80 anode, and the diode you mention only seems to be on 'line'.

The PCF80 is driven from the IF board, and the sync separator is TR9, fed from emitter follower TR8. If these transistors are OK, there's an electrolytic capacitor, between the two. Also a coupling cap on the board, before the signal leaves for the amp stage mentioned above. There's also a cap on the amplifier. Change these and try it.

By the way, if you want advice, try my site: www.oldtellys.co.uk

Cheers,

Steve P
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Old 29th Dec 2006, 5:02 pm   #3
Mike Phelan
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Default Re: GEC 2028 Restoration - Advice with Sync Fault

Dr W
Is both the frame and line sync weak?
The dual diode block is a pair of silicon diodes, so 1N4007s are fine, albeit a bit of overkill!

Have you a 'scope?

The colour beacon works from the killer, by rectifying the 7.8KHz ident signal, so will come on if there is colour present.

We may need a circuit to help you, although others may have better memories than me! I recall something like a 47k feeding line pulses to the aforementioned diode? Has it fried up?
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Old 29th Dec 2006, 6:31 pm   #4
Dr-Watts
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Default Re: GEC 2028 Restoration - Advice with Sync Fault

It appears to be line sync.

I've just had to swear at it... very loudly !

The lead from the tripler to the focus control broke down and made some unholy racket and very big sparks, so I thought 'I know, I'll just bung a new lead on it'.
A great idea until I broke the lead off the tripler trying to join a temporary new one on to it! (it's gone terribly brittle)

It's got to be said, it's been a year on and off, trying to find time to work on it and my patience is running very thin!

I photocopied the red book drawing at work and enlarged it, it's not too bad
The set is immaculate inside & out so I think it should be fixed & enjoyed.
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Old 29th Dec 2006, 7:55 pm   #5
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Default Re: GEC 2028 Restoration - Advice with Sync Fault

Replace the diode block with a couple of oa202 diodes. If you do not have them, try BY206. Malc.
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Old 30th Dec 2006, 11:51 am   #6
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Default Re: GEC 2028 Restoration - Advice with Sync Fault

I got away with 2x 1N4148 diodes in this area!
Other possibles are tag PL18/8 of LOPT broken or dry jointed, C503 & C504 (both 470pF), R502 (47K), R507 & R508 (both 330K).

The HVM Universal tripler I used in my CVC5 and G6 is sutiable for the GEC 2028, so presumably any "Universal" type should be ok.

They're superb sets, my fave of the dual standard CTV era. Very reliable once the usual problems are ironed out.

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