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Old 22nd Nov 2020, 9:15 am   #7
GreasedMonkey
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Join Date: Feb 2019
Location: Worcester, Worcestershire, UK.
Posts: 115
Default Re: GEC Junior Fineline - yet another fault.

I found myself with a bit of time yesterday evening, so I tried running up the set from a bench supply.

I removed PL2 from the main pcb, as this completely takes the sets own power supply out of the equation. (It also disconnects the volume control and loudspeaker, but I am only interested in picture just now). I powered it up with a requalted and stabilised 11V DC directly onto the 11V line of the main PCB.

Unfortunately the results were much the same. Very wavy picture, brightness control makes a huge difference to line frequency and the whole image seems to “jitter” a bit.

Seems there is something more sinister than supply issues going on there. I could see the supply current varying with the beam current as expected, but the11V from the bench supply was solid as a rock.

Extent of the distortion can be seen in the picture, especially the one with the lass stood in a doorway. The dark horizontal bars on the one image are not there in real life, they were added by my camera.
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