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Old 24th Jan 2018, 12:44 am   #1
rbm1973
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Default GEC 2110 picture distortion

Anyone had this problem with this chassis?

if you look at the testcard it has N/S distortion.

which after restoring the set this fault i have been unable to rectify.
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Old 24th Jan 2018, 11:19 pm   #2
FERNSEH
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Default Re: GEC 2110 picture distortion

Rest assured it's not the scanning coils which are faulty. There are certain adjustments associated with the pin cushion transductor. I don't have a service manual to hand right now in order that the pincushion correction controls can be identified.

DFWB.
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Old 25th Jan 2018, 12:30 am   #3
1100 man
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Default Re: GEC 2110 picture distortion

Hi,
I can't help you at all, but it's great to see someone using the Channel 4 test card It's the testcard I have the most fondness for and in my opinion, it's the most useful for linearity & convergence! I spent many, many hours in the early '80's using this card when CH4 was getting started. It was a real pain when they started showing 'Countdown' instead!
Happy memories of a small, seldom used classroom at school where I had a stash of TV's that I would attempt to repair during lunchbreak!
Cheers
Nick
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Old 25th Jan 2018, 2:51 am   #4
Argus25
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Default Re: GEC 2110 picture distortion

It does appear to have pincushion distortion, that could be probably be adjusted out on the E-W modulator circuit, but interestingly more on the right than the left and an error in that circuit usually gives a more symmetrical defect in the geometry. Ignoring that though, for the moment, looking across the center of the scan from left to right there is a horizontal linearity error with compression of the scan centrally and stretching on each side to some degree. I wonder if there is something wrong with the S correction capacitor value or if that capacitor is leaky or shorted. Worth checking, just in case.

Sometimes there are external magnets on the yoke or tube bulb that can distort the geometry of the raster, and affect all three beams the same if they are out of adjustment. It does seem the defect is more on the upper right side of the raster than elsewhere.
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Old 25th Jan 2018, 2:18 pm   #5
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Default Re: GEC 2110 picture distortion

Also interesting to note the distortion is worse on the right closest to the speaker. Incorrect speaker fitted at some point in the set's history?

What is surprising is how good the purity and convergence are despite the distorted images.

Also, is the Transductor ok and the correct type?

Brian.
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Old 25th Jan 2018, 10:12 pm   #6
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Default Re: GEC 2110 picture distortion

If I'm right this is a 90 degree delta crt? There are normally two adjustments to the pincushion correction, amplitude with a pot and phase using a coil. It looks as though the phase adjustment is well out.

Move the error at the top left to the centre of the screen using the phase coil and adjust the amplitude pot for straightest horizontals, there is some interactions so you'll need to experiment a bit.

John.
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Old 26th Jan 2018, 11:51 am   #7
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Default Re: GEC 2110 picture distortion

Still haven't found the service manual for the GEC C2110 series. The attachment shows the transductor circuit of the Pye 691. Although this is a hybrid receiver the circuits around the transductor will be very similar in the all transistor GEC C2110. The 0.047uF capacitor and the phase coil are adjusted to resonate at 3 X fH. A variable resistor across line windings of the transductor adjusts the amplitude of the correction waveform. So the adjustment procedure is: first find the phase coil and adjust it for a symmetrical shape at the top of the picture and adjust the amplitude control to straighten up the top of the raster.

DFWB.
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Old 26th Jan 2018, 12:15 pm   #8
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Default Re: GEC 2110 picture distortion

If the transductor is found to be faulty I'm sure I have a spare one. Check the 120ohm resistor in series with the line coils of the transductor.

DFWB.
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