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Old 23rd Feb 2019, 1:39 pm   #1
GreasedMonkey
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Default GEC Junior Fineline project.

Hi all,

I have now secured a set for my project, many thanks to Neil29 of this parish for the kind donation.

There are some nice signs of life from the set, the tube is nice and bright and some good and loud audio crackles for the dirty pot, but no snowy screen or white noise, just a blank raster with a slight hint of fly back lines with contrast and brightness fully up.

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.

Thanks in advance.
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Old 23rd Feb 2019, 3:41 pm   #2
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Default Re: GEC Junior Fineline project.

I can't find a circuit online but I would check the LT supply to the tuner first. Then check the voltages on the transistors in the IF strip if there are any lockfit transistors they can be a source of trouble.
This is assuming it hasn't got an MC1327 or similar chip in the If circuits they were a very common problem on the Decca portables which are a similar age. The chip would fail causing blank raster and sometimes strange radio breakthrough I think on the Decca there were two chips in the IF one or both could fail causing problems.
I can't remember if the GEC uses all transistors or not I didn't see many when they were current....


Rich.

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Old 23rd Feb 2019, 5:02 pm   #3
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Default Re: GEC Junior Fineline project.

Yes the set is all transistor.

It looks like itís had a few repairs over the years.

I seem to have lost the nice bright screen now, just a single line through the centre. I think I need a circuit diagram to go any further, I have little-to-no experience of these things.
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Old 23rd Feb 2019, 7:50 pm   #4
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Default Re: GEC Junior Fineline project.

Quite comprehensive coverage including circuit in Newnes Radio & TV Servicing books,
1973-74 pages 400-418, also later version revisions in 1974-75 volume pages 306-307.
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Old 23rd Feb 2019, 9:19 pm   #5
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Default Re: GEC Junior Fineline project.

Where can I obtain this information?

I am an electronic engineer by trade and have basic tools, meters, scope, function generators etc, but without the circuit data these are not much use.

I have had a quick look and the scan coils check out, 13 ohms out of circuit. I have found a suspect inductor but I don’t know specs of the component (L202) which appears to be something to do with vertical deflection.
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Old 23rd Feb 2019, 9:40 pm   #6
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Default Re: GEC Junior Fineline project.

Quick update:

I have a full raster again. I luckily L202 was open circuit right at the end of the winding so I managed to repair it, itís lost half a turn, but probably close enough.

Now on to the lack of video / audio.
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Old 24th Feb 2019, 11:54 am   #7
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Default Re: GEC Junior Fineline project.

Back onto it for a little while this morning,

In answer to Rich comments from yesterday, the set is all transistor, there is a demodulator IC for the audio, and the audio amp is a single IC job. No IC for video demodulation, but the thing has lockfit transistors all over the place.

Anyhow, I think I have identified where I should find demodulates audio and video signals so this evening when I get back to it I think I will inject some signals into it with a function generator and see if that side of things is all working as it should.

Still coming up short on the hunt for any data on the set though, it would make life so much easier. Does anybody know if the chassis is shared with any other sets that may have information easier to find?
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Old 24th Feb 2019, 12:32 pm   #8
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Default Re: GEC Junior Fineline project.

Sorry I don't have a manual but I would start by checking voltages on the BF196 & BF197 transistors, no or low collector volts would suggest a supply fault. Check particularly between the base and emitter for around 0.6 - 0.7V, replace any that are wide of the mark. If the BF196s are less than 0.5V then you may have an AGC fault.

John.
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Old 24th Feb 2019, 12:48 pm   #9
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Default Re: GEC Junior Fineline project.

Quote:
Originally Posted by GreasedMonkey View Post
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.
Here's a thread about one of these sets, and at the bottom of the first post is a link to the service data

Regards,
Lloyd
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Old 24th Feb 2019, 1:28 pm   #10
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Default Re: GEC Junior Fineline project.

Thanks Lloyd, I will register later today and have a gander.

I may have more luck now I know to search for 2114. There is nothing in the model number box on my set. I assume it was a sticker of some sort that fell off years ago.
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Old 24th Feb 2019, 4:21 pm   #11
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Default Re: GEC Junior Fineline project.

A little more progress, thanks to data at the link from Lloyd.

I now have a functioning tuner and nice clear audio. Confirmed by using a VCR as a source.

Still no picture, just a blank, flickering screen. Work has stopped for a while now. I shall move on to the video stages later today.
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Old 24th Feb 2019, 7:37 pm   #12
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Default Re: GEC Junior Fineline project.

Armed with more information and a sense of confidence (not sure if it was the success with the tuner or the cider that came with Sunday lunch) I decided to go back to investigate the lack of video, but sometime between before lunch and now, my scope has decided it does not want to play any more.

I could probably fix it if I had a scope to investigate with.
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Old 25th Feb 2019, 11:33 am   #13
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Default Re: GEC Junior Fineline project.

So the 2 steps forward, one step back continues.

After searching for my old handheld scope and finding it still works, I set about investigating the lack of video, working my way through the circuit diagram to find only steady DC levels being fed to the vision detector. Upon poking R117 with my scope probe I was rewarded with a brief picture. Prodding that area of the PCB generated in intermittent picture to appear. So powered off and set about looking for dry joints, again. I had already scoured the PCB under a magnifier and found a few, but maybe I had missed one. I couldn't see any so decided to re-solder all the joints in that area on the thinking that prodding the PCB was making a connection somewhere.

Now I am back to a blank raster and no amount of prodding will produce a picture. My theory now is that a component has failed short circuit and my prodding was actually breaking a connection rather than making it, I suspect a filter or decoupling capacitor somewhere.

What do others here think of this current theory? or am I barking up completely the wrong tree? I have little to no experience with these sets so would welcome the wisdom of those more experienced.

Any advice will be gratefully received.

Thanks.
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Old 25th Feb 2019, 4:19 pm   #14
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Default Re: GEC Junior Fineline project.

Does your hand-held 'scope have enough bandwidth to display video? Many older ones dont.
Personally, I would work backwards from TR107 to the diode D103, which is the vision detector diode if the scope will display video. If not, use voltage measurements.
Vision detector diodes are always suspect in my experience, and replacement is sometimes the only way to prove them faulty. I would think there was a signal up to the video detector, as you say you have sound, which is tapped off the collector of the final video I.F. amplifier via R145, so the I.F. circuits can hopefully be considered Ok.
I've never worked on one of these, but at least it looks a nice easy chassis to work on. Dont forget there may be up to 100V. on the collector of TR107...Hope the Hand-Held 'scope will stand it.Tony.
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Old 25th Feb 2019, 4:49 pm   #15
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Default Re: GEC Junior Fineline project.

My handheld scope can display video. It was a good one back in its day. I don't know the specs off hand, but I did shove the probe into the video out of the VCR to confirm settings before I began searching.

I get what you are saying about the audio, and it being tapped off L105. So logic would say the fault lies to the right of this inductor in the circuit diagram.

When checked with a DVM the collector of Tr107 measures 58V which does seem a little low, but the book says "can vary significantly with signal".

Hopefully I can investigate a little more tonight.
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Old 25th Feb 2019, 5:54 pm   #16
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Default Re: GEC Junior Fineline project.

Quote:
Originally Posted by boxdoctor View Post
Vision detector diodes are always suspect in my experience, and replacement is sometimes the only way to prove them faulty. .Tony.
Very good advice! I had a right run around with a video fault on a KB VC4 that turned out to be the detector diode. I cannot remember now why it lead me a merry dance I do remember it was inside one of the screening cans though...

Rich
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Old 26th Feb 2019, 10:43 am   #17
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Default Re: GEC Junior Fineline project.

A little more progress, but I will be honest, I don't know why just yet. I need to go back to the diagram to work out what was going on.

I was quite tired last night so I decided that rather than do thinking I would spend a little bit of time going over the audio PCB as there are various crackles and pops whenever this is touched. So I removed it, cleaned the plug and socket, resoldered a few suspect looking joints and replaced 2 capacitors and a resistor.

At this point I planned to put the audio board back in, power up the set to confirm the crackles and pops had gone and go to bed. But upon powering the set I was greeted not only by clear audio the no longer popped and crackled when the board was touched, but also by a feint image, it was waving about and scrolling like a good un, but it was an image. At this point I was back to suspecting a bad connection somewhere, but despite all my efforts poking, prodding, shaking, even a good thump. I could not make the picture go away again.

Filled with renewed enthusiasm I squirted a little contact cleaner in the contrast pot and gave it a wiggle. I did a bit of fiddling and managed to obtain a watchable picture, not perfect by any stretch, but I will make the final adjustments with the Freeview test card when all is said and done.

There are still issues, there are rather annoying flyback lines visible and it seems incredibly fussy on the Vert and Horiz hold adjustments.

But hey, Progress is progress even if I don't know why or how.
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Old 27th Feb 2019, 12:34 pm   #18
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Default Re: GEC Junior Fineline project.

Hi G.M.,
I would be inclined to check the spark-gaps on the CRT base next for muck in the gaps. Check T202 Pin ! for a dry joint, as this is the source of the flyback blanking voltage (via R247 which could be high or O/C). Also you may simply have the brightness set too high.
Getting back to the video fault, my first candidate for replacement is D103. Unfortunately inside one of the cans. Hard to get at, but worth the effort, as they only cost pence and it's a strong candidate for being faulty. If you haven't found it by this stage, TR106 & 107 and the associated Rs and Cs would need to be investigated next.
As the sync appears dodgy from your remarks, I would think it is most likely to be around the circuitry between L106 and TR106, as the sync is taken off from the collector of TR106. Tony.
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Last edited by boxdoctor; 27th Feb 2019 at 12:40 pm.
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Old 28th Feb 2019, 10:56 am   #19
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Default Re: GEC Junior Fineline project.

Some more progress.

Looks like someone had been here before me. R202 had been removed and D201 had been moved, it cathode was connected to C201 and the anode connect in series with a 330K resistor which was then connected to the junction of R133 and R131. after putting this back to the circuit diagram I now have a picture that is much led fussy on the vertical and horizontal hold. Still the flyback lines remain. This evening I will scope up R139 and see what I have there in the way of blanking pulses.
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Old 28th Feb 2019, 1:26 pm   #20
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Default Re: GEC Junior Fineline project.

Good thing you spotted the "mod". That's saved a lot of going round in circles! I hate bodgers, a fault is there to be found, not masked.
Should not be too difficult to spot where the Flyback suppression pulse is disappearing. R139 and C218, and dry joints on them are looking like the prime suspects now. The video may well improve when you get that sorted, too. Tony.
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