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Old 18th Jan 2020, 7:56 pm   #41
slidertogrid
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Default Re: GEC Junior fineline picture problem.

From my experience any hum on the LT line of a Transistorised mono portable results in a hum bar or large 'Kink' in the picture travelling up the picture causing the frame to roll when it reaches the top of the screen.
I still think the fault lies with the line speed being off rather than a frame fault.
Can you resolve a line locked picture or are there many pictures side by side when you adjust the line hold?
Have you checked the discriminator diodes? I would try to get the line speed right first and then see if you still have low picture height.
I don't profess to be an expert just my thoughts....
Rich.
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Old 18th Jan 2020, 8:28 pm   #42
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Default Re: GEC Junior fineline picture problem.

Quote:
Originally Posted by slidertogrid View Post
Have you checked the discriminator diodes? I would try to get the line speed right first and then see if you still have low picture height.
......same as I suggested back in post 21.....
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Old 18th Jan 2020, 9:01 pm   #43
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Default Re: GEC Junior fineline picture problem.

Success.

I remembered having trouble with this set first time round due to the aged pcb and lack of connection between the sides of the board through the track holes. I went back and soldered the component legs on the top side of the PCB as well.

I was rewarded with a full screen image, no horizontal lock, but full screen. A quick fiddle with L201 and all is well.

Thanks all. Iím sure there will be a next time.
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Old 18th Jan 2020, 9:56 pm   #44
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Default Re: GEC Junior fineline picture problem.

Very well done on your perseverance, itís paid off!

Now youíll be ready for the next project!

Another TV?

Cheers . SimonT.
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Old 18th Jan 2020, 10:10 pm   #45
slidertogrid
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Default Re: GEC Junior fineline picture problem.

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Originally Posted by Sideband View Post
Quote:
Originally Posted by slidertogrid View Post
Have you checked the discriminator diodes? I would try to get the line speed right first and then see if you still have low picture height.
......same as I suggested back in post 21.....
Yes, but we didn't get an answer to that (Sensible, IMO) suggestion so I was asking if it had been done. We got a load of theory as why the fault wasn't in the line stage and we started to go all around the houses Ö
Glad it's fixed though!
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Old 19th Jan 2020, 10:34 am   #46
GreasedMonkey
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Default Re: GEC Junior fineline picture problem.

In post 12 is a scope trace confirming correct line speed. After this I thought it was accepted that the fault was nothing to do with the line, but must have lay in the field. I saw no reason to poke about that part of the circuit any further.
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Old 19th Jan 2020, 10:42 am   #47
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Default Re: GEC Junior fineline picture problem.

The latest on this set is that another disaster has befallen it.this time completely caused by my own clumsiness and Han fisted attempts at reassembly.

I left the set running for a good few hours last night, while I drank tea and kept an eye on it. (For the sake of the set you understand, not at all because I felt like an evening in front of the telly).

Anyway, after a good few hours of trouble free operation, I decided to put it back together and go bed. Now, I lined up the chassis and proceeded to slide it all back into place by pushing on the metal work with my thumbs, or so I thought, stupidly one thumb had missed and was actually pushing on L201 which promptly snapped the plastic former, breaking the windings, both windings at the centre point and one at the other end.

I tried to solder them back together, but now can’t get a stable picture, it wobbles about all over the place in the horizontal plane.

If anybody has one of these inductors going spare, I will very much like to swap some small portraits of the queen for it.
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Old 19th Jan 2020, 3:34 pm   #48
GreasedMonkey
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Default Re: GEC Junior fineline picture problem.

Quote:
Originally Posted by thermionic View Post
Very well done on your perseverance, itís paid off!

Now youíll be ready for the next project!

Another TV?

Cheers . SimonT.
I quite fancy one of those mono portables from the 80ís next. They were normally about the 12Ē mark and had a single rotary tuner.

But letís see if I canít put right my ham-fisted butchery of this inductor first.
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Old 14th Feb 2020, 4:10 pm   #49
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Default Re: GEC Junior fineline picture problem.

Well another day of mixed fortunes with this set.

Many thanks to Dazzlevision, who supplied me with a replacement line oscillator coil, but from a thorn chassis. This could did not work as it was, but did provide me with a new former. I sat and transferred the windings from my smashed former into this one and managed to get a raster on screen, but the speed was way off. Today I went back to the set and scoped it up to see how far off it was, then took a wild guess at adding 6 turns to the top winding. A second poke with the scope showed this to be too far, so I removed 4 of these new turns and managed to get a stable picture. The core was not far off centre so plenty of adjustment either way. I was happy with this. Left it running for a while and after about an hour, the picture disappeared. Just a blank raster. I traced this down to L111 having gone open circuit. After repairing this I left it to run again for a while and then put the chassis back in and closed the set up.

Later on, while watching TV the blooming this gave up again. Now suffering frame collapse once again. I guess the scope will be back out again sometime soon.

I am seriously considering giving up with this set. I do remember taking many trips to the local repair shop with dad when I had one of these as a young un, so that one was never particularly reliable. Eventually the engineer in the shop did one last repair and said it was not worth bothering with if it packed up again. A few months later that one lost the picture and was replaced with a 12Ē single rotary tuner jobby, (I donít remember the make or model) but that thing worked for years and I ended up taking that into student digs when I went to uni.
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Old 15th Feb 2020, 2:07 pm   #50
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Default Re: GEC Junior fineline picture problem.

So here we are again. Another couple of hours spent with the set.

Currently it is once again up and running. And I was very careful not to smash anything on reassembly. I think the picture height needs reducing every so slightly and the video level is a tiny bit below the 3V Pk-Pk it should be, but I will spend time on getting the final adjustments spot on after it has proven itself capable of trouble free operation for a while. It is perfectly watchable as it is.
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