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-   -   GEC Junior Fineline - yet another fault. (https://www.vintage-radio.net/forum/showthread.php?t=173279)

GreasedMonkey 19th Nov 2020 8:37 am

GEC Junior Fineline - yet another fault.
 
1 Attachment(s)
This set has been used little but often. It’s main use is for me to watch a bit of news while I have breakfast at the kitchen table so tends to be on for about 20 minutes a day.
However, yesterday evening I sat at the kitchen table to do a small job and decided to put the telly on. I was greeted with the left half of the picture on the right hand side of the screen and vice-versa. Along with this the image was quite distorted with straight lines not being very straight. Deciding this would be more interesting than my planned task, I picked it up and took it out to my workshop.

When I put it on in the workshop the horizontal frequency was off, but not so far that I couldn’t correct it with the hold control. Now the image was as it should be, but adjusting the brightness or contrast now changes the horizontal frequency, and the picture is sort of wavy. It’s like watching it on a flag blowing in the breeze if that analogy makes any sense to anybody out there. It was at this point I left it and went back to what I should have been doing all along.

As this forum has been so helpful with past faults, I was wondering, can any of the experts on here shed light on what may be happening here? It’s not something I have seen before, but I have little experience compared to many on here.

Thanks in advance.

murphyv310 19th Nov 2020 9:43 am

Re: GEC Junior Fineline - yet another fault.
 
You should set the control midway between going out of lock. As you increase the brightness and contrast the load increases on the line stage which is reflected back to the power supply which can alter line frequency.
All quite normal.

GreasedMonkey 19th Nov 2020 9:55 am

Re: GEC Junior Fineline - yet another fault.
 
Quote:

Originally Posted by murphyv310 (Post 1312065)
You should set the control midway between going out of lock. As you increase the brightness and contrast the load increases on the line stage which is reflected back to the power supply which can alter line frequency.
All quite normal.

Cant say I have noticed before, but this makes sense. Maybe I have an issue with poor regulation of the supply then, as this seems excessive. I can go from out of lock one way, right through to out of lock the other way just by varying the brightness. This is definitely new as I do tend to alter the brightness often depending on ambient light in the room.
Certainly the Wavy picture is a new thing.

Welsh Anorak 19th Nov 2020 11:18 am

Re: GEC Junior Fineline - yet another fault.
 
I'd go back to basics, which is the power supply, especially as there have been problems there before. If the voltage is low then the line frequency could be off and the waves (hum?)appear. Hang a meter on the HT and see if it's correct and doesn't vary with brightness. That will point you in the right direction.

murphyv310 19th Nov 2020 11:47 am

Re: GEC Junior Fineline - yet another fault.
 
Certainly not right if it goes from one side of the lock to the other with beam current.
As Glyn says check the power supply first, the other issue could be weak sync.

GreasedMonkey 19th Nov 2020 11:52 am

Re: GEC Junior Fineline - yet another fault.
 
I think I will run it up on a regulated Bench supply this evening, see if that makes a difference. I have a 5A regulated DC supply not currently in use, I will try that.

GreasedMonkey 22nd Nov 2020 9:15 am

Re: GEC Junior Fineline - yet another fault.
 
2 Attachment(s)
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.

Restoration73 22nd Nov 2020 7:07 pm

Re: GEC Junior Fineline - yet another fault.
 
Like Thorn 1590 flywheel sync means the lock should be solid. It seems a hum problem.
The chassis is covered in the April and May 1976 issues of Television magazine;
https://worldradiohistory.com/Practi...n_Magazine.htm

GreasedMonkey 22nd Nov 2020 8:17 pm

Re: GEC Junior Fineline - yet another fault.
 
Forgive me if it is my misunderstanding, but I would take the word ‘hum’ to mean a low frequency noise of mains derived origin propagating through the circuit. Is there a differing description of ‘hum’ in the TV world. Sorry, but my background is not tv or even AV based.

Surely if it were mains hum causing the issue, it would be evident in the audio as well? There is no noticeable buzz from the loudspeaker, and running the set up from a bench supply would eliminate any mains derived issues.

I know when one leg of the rectifier packed up it played merry hell with both picture and audio. This is different to that, though I understand that that would have been an extreme example.

Top Cap 22nd Nov 2020 9:37 pm

Re: GEC Junior Fineline - yet another fault.
 
Could be the sound stages are powered from a supply derived from the LOPT with its own smoothing components so immune at this time from ripple on the main supply.
The problem you show reminds me of TV I had fun with, hum bars upsetting the video and sync. Spent ages looking for the fault until I discovered that the steel frame that encircled the circuit board had numerous dry joints and was meant to be the main ground bus. Once re-soldered all the way round the set worked great. I had another set, same make and model, with similar fault and only took a few minutes to fix this time.

GreasedMonkey 23rd Nov 2020 1:58 pm

Re: GEC Junior Fineline - yet another fault.
 
Top Cap, I have checked the steel frame as suggested, and reflowed all of the solder points. I also found the ground strap to the tuner was open circuit, only held together by the outer sleeve so have replaced this also. But sadly no change.

Unfortunately I feel the end may be in sight for this set as the main PCB has had so many repairs and previous repairs and bodges done to it, it is starting to be in a bit of a sorry state.
Many PCB tracks are bridged with its of wire or lots of solder, or just missing entirely and bits of wire used instead. It has gotten to the state where I dont feel it will ever be a reliable set.

May be a long shot, but I will try a wanted post for a replacement PCB. Maybe somebody out there has one with a duff tube or smashed case. As I type this I am wondering if the PCB drawings exist anywhere? I could easily get one made if I could get hold of tracking drawings.


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