GEC 2028 Line speed changing - UK Vintage Radio Repair and Restoration Discussion Forum

Dr-Watts · 7th Jul 2007, 11:00 am

Hi all.
This 2028 is becoming a regular on here innit !

Now the sync fault is sorted after replacing the 2 trannies, all of the resistors and caps, next fault...

The line speed seems to be running away; when first switched on all seems ok, after 5 minutes or so the picture loses hold.
You can chase it up the horizontal hold control until it runs out of travel (anti clockwise). and for this you get another couple of minutes' viewing.
I'll bung a scope on it later and check the frequency etc.

Can anyone remember a fault like this on this chassis ?
Or even suggest anything, please?
Would I be right to suspect the PCF802?

Here's a couple of before and after scope traces and the GEC under surgery.

Kind Regards

Dave W

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ukcol · 7th Jul 2007, 12:04 pm

Hi Dave

Has this line speed fault only appeared since you fixed the sync problem?

If so, you may have fitted an unsuitable component type; I would particularly suspect C513 which must be a close tolerance, high stability capacitor.

A silver mica would be ideal.

Dr-Watts · 7th Jul 2007, 4:39 pm

Well...
It turned out that it was a speed problem all along and I was just being stupid suspecting the sync stage; however, as you can see the pulses are now not noisy so all in all, I'm glad I changed the above anyway

Regards

Dave W

Focus Diode · 7th Jul 2007, 4:54 pm

Line Running at wrong speed or control one ended:

PCF 802, diodes D501 (I got away with 2x1N4148s), C513 (820pF), C514 (0.22uF), C510 (0.1uF), R519 (680ohm), R510 (330K), R507 (330K), C503 & C504 (both 470pF).

It's also not unknown for the hold controls to change value to cause this condition. As ukcol says the pF capacitors must be close tolerance, high stability types.

Hope that's some help.
Cheers,
Brian

7th Jul 2007, 11:00 am	#1
Dr-Watts Heptode Join Date: Dec 2006 Location: Milton Keynes, Buckinghamshire, UK. Posts: 696	GEC 2028 Line speed changing Hi all. This 2028 is becoming a regular on here innit ! Now the sync fault is sorted after replacing the 2 trannies, all of the resistors and caps, next fault... The line speed seems to be running away; when first switched on all seems ok, after 5 minutes or so the picture loses hold. You can chase it up the horizontal hold control until it runs out of travel (anti clockwise). and for this you get another couple of minutes' viewing. I'll bung a scope on it later and check the frequency etc. Can anyone remember a fault like this on this chassis ? Or even suggest anything, please? Would I be right to suspect the PCF802? Here's a couple of before and after scope traces and the GEC under surgery. Kind Regards Dave W __________________ Do you have the scope to be a TV repair man Last edited by Mike Phelan; 14th May 2008 at 3:55 pm. Reason: Edited typos

7th Jul 2007, 12:04 pm	#2
ukcol Rest in Peace Join Date: May 2003 Location: Harlaxton, Lincolnshire, UK. Posts: 3,944	Re: GEC 2028 Line speed changing ! Hi Dave Has this line speed fault only appeared since you fixed the sync problem? If so, you may have fitted an unsuitable component type; I would particularly suspect C513 which must be a close tolerance, high stability capacitor. A silver mica would be ideal.

7th Jul 2007, 4:39 pm	#3
Dr-Watts Heptode Join Date: Dec 2006 Location: Milton Keynes, Buckinghamshire, UK. Posts: 696	Re: GEC 2028 Line speed changing ! Well... It turned out that it was a speed problem all along and I was just being stupid suspecting the sync stage; however, as you can see the pulses are now not noisy so all in all, I'm glad I changed the above anyway Regards Dave W __________________ Do you have the scope to be a TV repair man

7th Jul 2007, 4:54 pm	#4
Focus Diode Octode Join Date: Jan 2006 Location: Borough of Gateshead, UK. Posts: 1,420	Re: GEC 2028 Line speed changing ! Line Running at wrong speed or control one ended: PCF 802, diodes D501 (I got away with 2x1N4148s), C513 (820pF), C514 (0.22uF), C510 (0.1uF), R519 (680ohm), R510 (330K), R507 (330K), C503 & C504 (both 470pF). It's also not unknown for the hold controls to change value to cause this condition. As ukcol says the pF capacitors must be close tolerance, high stability types. Hope that's some help. Cheers, Brian