GEC Junior Fineline project.

[GreasedMonkey]

Some progress to report.

progress stalled somewhat recently as everything got horribly noisy all of a sudden, Nasty buzz on the audio and impossible to get a lock on the picture. Scoping up the power supply showed a ripple frequency to match half wave rectification, I assume one of the diodes in the rectifier has decided not to play any more.

None of the component suppliers I usually use had the correct part, I assume it went obsolete some time ago. I could find a suitable replacement from RS or Farnell bit that was going to have to wait until Monday as my account details are at the office.

anyway, last night it dawned upon me that the set is 12v DC as well. So armed with a small bench supply I powered it up and was happy to see all the noise had gone.

I have now solved the fly back issue. It seems these sets are quite particular about the voltage of the fly back blanking pulse. I replaced the biasing resistors and the fly back was much reduced, only now visible at very high brightness setting. Neither resistor has failed as such but both were out of spec, I assume just down to age. Comparing the signals before and after resistor replacement, raising the blanking level from 3.8 to 4.2V had almost got rid of the fly back lines completely. Assuming most of the other resistor in the set would be similarly out of spec (other than ones I have replace already) I decided to try adding a trimmer pot in series to try and fine tune the level.

Raising the level a bit more (4.3V) has banished the flyback completely.

Also, while searching for a trimmer pot, I found a bag of MR504 3A 400V rectifier diodes.

[GreasedMonkey]

4 diodes successfully installed in bridge formation and all is well again.

Now I have a picture and sound that I am happy with, I turn my attention to the case. During my investigations it had got to the stage where the only thing still secured in place was the tube, so this has now been removed so I can deal with an empty case. It has gone a sort of yellowy-brown colour over time. At first I thought it was nicotine stained, but I think it has been had by the sun as there is a loop of white where the cable would have been around the two hooks on the back. No amount of cleaning is bringing it back to its whiteness so I am thinking along the lines of a spray job now.

If anybody has any advise for restoring these plastic cases, I would be pleased to hear it. I did do a small abrasion test on an unseen area of the case and the yellowing is quite deep into the plastic.

[19Seventy7]

Have you thought about the "Retrobrite" technique? It seems quite a popular technique, especially for older computers.

This link might help you
https://www.youtube.com/watch?v=qZYbchvSUDY

[GreasedMonkey]

I have just been looking at the retr0brite stuff as it was suggested over on VRAT.

I have also found a few disaster stories and as a result I think I am going to rule that out. The plastic has gone a bit brittle with age so I think this would be asking for trouble.

Worst case is I just clean it all as best I can and live with the yellow.

[19Seventy7]

That sounds fair enough, I wouldn't want to take the risk either if it doesn't always go to plan.

Good luck!

[Vectamart]

Originally Posted by GreasedMonkey

Can anyone point me in the direction of service information for the G.E.C. Junior Fineline set please? Or does anyone know of any common faults for this set.

I have an ERT Service Chart that I could scan if that would be of help.

[GreasedMonkey]

Thanks for the offer.

Although o have the set working now, I would still be interested in this.

Cheers.

[Vectamart]

I'll scan it for you as soon as I get an opportune moment.

[GreasedMonkey]

Sorry its been a while for any progress, I have been distracted by life for a few days.



Anyhow, the set is all back together and resplendent in its nice new white coat.

All that remains is final adjustment, but I am struggling with this. I have some geometry issues. The picture is too low and to the right, not in he centre. The picture seems narrower at the top than the bottom and any vertical lines seem to get a little kinky.

The two magnet rings on the back of the tube are labelled as "picture centering" in the service info, but as much as I fiddle with these rings, I cannot get it any more 'Centre' without loosing some. I can raise the picture, but this results in an arc of darkness in the top right corner. anything else I try just results in some very odd picture shapes and positions. For now I have realigned said rings with my sharpie marks I made before I started to fiddle. Is there a general procedure for setting them rather than just rotating them at random and hoping for the best, as this method has not served me well so far.

Any other hints and tips for setting up will also be very welcome.

[Welsh Anorak]

Hi. There may be a couple of permanent magnets sticking out from the sides of the scan coils which are on soft metal so you can move them around to correct this. It's of course possible your small CRT doesn't have these, in which case you might see if you can find a scrap large-screen mono set which could donate a pair. They are about an inch long and are close to the bowl of the CRT..

Don't forget the average viewer might not have been too fussy! An old-timer in the trade told me of a customer of his who used to have a steel rule and callipers to measure the roundness and position of the circle of the test card after service. Slightly out and he was back for the evening....

[GreasedMonkey]

Thanks Glyn.

There is no mention of any magnets other than the two rotating rings with the little tabs on in the information I have for the set, and I dint recall seeing any, but I have not particularly been looking for them.

How powerful do these magnets need to be? I have access to ferrite rubber, ferrite, rare earth and neodymium magnets. I also have access to a magnetiser so I could theoretically make a magnet or 2 of whatever strength is required.

[ms660]

The rings are very interactive, also make sure the scan coils are fully shoved up on the neck.

Lawrence.

[GreasedMonkey]

I have discovered this. There seems to be no discernible pattern as to what movement of what ring has what effect on the picture. I was hoping somebody would be able to suggest what ring did what as I had given up trying to decipher and kind of logic from them. Luckily I marked the starting positions, so I was not going to make things any worse.

[ms660]

It's an art due to the infinite number of combinations, hard to explain how to do it over the web, just comes naturally when it's the day job, good luck anyways.

Lawrence.

[GreasedMonkey]

hard to explain how to do it over the web

Please try. I would be grateful for any hints or tips right now. This is the first TV I have messed with for a good 25 yrs and never been involved with one to this extent before so any words of wisdom from those more experienced would be very useful.

[ms660]

Just keep shuffling the rings, providing you don't physically damage things no harm can be done, also make sure the scan coil assembly is fully forward and in proper contact with the CRT bowl.

Lawrence.

[GreasedMonkey]

Thanks. I will check the scan coil assembly is fully home this evening (supposed to be working right now) but I cant see why it wont be, not messed with the tube at all other than shuffling the rings last night.

Despite all of the shuffling I tried I could not lift the picture. Or I could lift the picture but then the top right corner was cut off at a kind of chamfer. I can adjust the picture to fill the screen, but then I am missing some off the bottom.

I will feed it a testcard again this evening and have another play.

[1100 man]

Hi GM,
One ring tends to shift the whole picture diagonally. The other ring tends to shift it diagonally in the opposite direction. Moving both rings together also has an effect so it is usually very easy to get the picture where you want it.

If it's cutting off the corner, that is often because the scan coils are too far back. The beam is running into the cone of the CRT before getting to the screen. Try slackening off the scan coil clamp and (after making sure the coils are free to move) make sure they are as far forward as they will go.

The small magnets used to correct raster distortion are usually small cylinders 3/4" long. These are very weak. The magnetised tip of a screwdriver is more than powerful enough to experiment with.

It would be worth posting some pictures of the raster with a test card and also the scan coil assembly.

All the best
Nick

[GreasedMonkey]

Hi Nick.

Here are some pictures, test card and scan coils as requested.

I know the rest card is squished, I am not worried about that, the only test card I have access to is with a freeview box. The trouble is, the one box I have has only options for 16:9 or letterbox 4:3.
The freeview box I intend to use with this set has option for 4:3 pan and scan so keeping the aspect ratio correct and loosing the edges, but this box does not support red button services so I can’t get a test card with it.
This was as good as I can get after having another play last night. The scan coils are as far forward as they will go, I could not find any permanent magnets to adjust.

[Lloyd 1985]

Just looking at your pictures of the scan coils, I noticed the spikes sticking out of it nearest the tube bowl, is there anything on any of them? I’m wondering if there would have been some sort of magnets pushed onto the spikes for tweaking the picture, but not on all of them, just where they were needed?

Regards
Lloyd