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Old 28th May 2020, 12:13 pm   #441
deepspacedaz
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Default Re: Fixing a GEC BT 302 Television

thank you for the information
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Old 29th Nov 2020, 2:25 pm   #442
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Default Re: Fixing a GEC BT 302 Television

Thread reopened at Heatercathodeshort's request.
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Old 29th Nov 2020, 2:36 pm   #443
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Default Re: Fixing a GEC BT 302 Television

Thanks Graham.

Thanks for sending your receiver and timebase panels from your GEC BT302 received yesterday [Saturday]

First to tackle was the timebase panel. On examination it was discovered that a number of dry joints were evident and a couple of the new capacitors were of the incorrect value. The use of non leaded solder will aggravate this with vintage receivers.

I thought the best approach was to remove all black GEC capacitors from the board, together with the replacements that you had fitted and with the aid of the GEC service manual, rebuild the board with everything hopefully in it's correct positions.

With the board cleaned up it was a simple matter to fit high grade modern capacitors knowing that in this department at least, everything should be correct.

With the old capacitors removed and the printed circuit cleaned up it was time to fit the new components. It didn't take long to do this and I was very tempted to let INTERLACE my pet Orangutan do the job but he scurried from the workshop having read the saga of the history of this BT302.

With the new capacitors fitted I decided to fit a new main frame linearity preset. This passes a heavy current and often failed. The GEC mod was to fit a 120K resistor across the track on the reverse side of the board.

All new solder joints were sealed with varnish to give a neat and tidy appearance.

With everything carefully checked I fitted the panel to my chassis using my set of valves and powered it up.

The line note was soon heard and a few seconds later a raster appeared on the screen. It was lacking height but this was soon sorted out by means of adjustment to the height and linearity controls. It was noted that both the line hold and frame hold controls were at the ends of their travel to obtain correct lock. Sync was very solid and a look at the circuit suggested a check on a couple of resistors should clean the problem up and it did. R90 a 360K 5% connected from the slider of the line hold to the grid of the oscillator read 390K. Due to it's odd value this is obviously a critical component and with a couple of resistors in series brought the line hold to the center of it's track. In a similar situation, R105 390K read high and a replacement brought the frame hold to mid travel.

Next to examine was the receiver unit/IF panel. Upon removal it appeared to be completely original and when fitted produced a fair picture without adjustment but where was the sound? Not a click or trace of hum from the speaker and my cynical approach led suspicion on the audio output transfromer. A quick check on the anode of the output valve read zero volts but a check on the HT side of the transformer also showed ZERO!

A quick check on the circuit revealed the supply to the output stage is derived via a 470 ohm 2 watt resistor and a 32uf, part of a twin can electrolytic. A meter short confirmed a very heavy leak at this point but a check revealed that the 32uf was innocent. The actual short was caused by the tone correction capacitor C90 .01uf. It is connected from the anode of the output valve to chassis and was completely S/C. A replacement brought the sound back with a roar and all was well. Fortunately the components used by GEC are of very high quality. The black moulded capacitors had a very long service life and even today rarely shut down a chassis completely. The audio output transformer appears unaffected by the overload but the 470ohm supply resistor looked a bit stressed and was retired from duty.

I decided to replace the remaining black moulded capacitors. It seemed a shame to risk further breakdowns after having travelled such a long road. I also replaced the screen grid decoupling capacitor to the vision IF amplifier V5 Z329 Mazda 30F5. These tend to crack and go O/C resulting in the stage bursting into oscillation producing a bright white screen with the video amplifier glowing red!

With the IF board refitted it was only necessary to adjust the two beehive trimmers, C56 and C58 the sound rejectors to obtain a very steady and reliable picture and sound. These are critical adjustments with all GEC chassis from the BT2147 to the end of genuine GEC television production at Coventry.

I will give the chassis a long soak test before returning them to Darren. I hope this clears up this long running saga.

Components replaced. TIMEBASE BOARD: C113, C112, C110, C111, C114,C115,C118,C117, C116, 120, C126, C123, C119, C124, C108, C107. VR106 Frame lin control preset 250K + 120k mod resistor.
[16]IF/RECEIVER:C61, C60,C91, C44,C45,C67,C74,C77, C79,C85,C90 and R41 [burnt].

I would add that many of these capacitors are probably 'serviceable' and I would probably have left a number in place had it been my own receiver but Darren is a long way from Horsham and the less chance of a breakdown is well worth the trouble of replacing them.

Well it's over to you Darren. I've post them off early week weather permitting!

Pictures show the two PCBs and the results. Regards, John.
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Old 29th Nov 2020, 5:13 pm   #444
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Default Re: Fixing a GEC BT 302 Television

Lovely write up John. Perhaps you could start a "factory refurbished" panel service, put Interlace to work!
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Old 29th Nov 2020, 5:18 pm   #445
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Default Re: Fixing a GEC BT 302 Television

Great to see this resolved at last, nice writeup John.
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Old 29th Nov 2020, 5:56 pm   #446
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Default Re: Fixing a GEC BT 302 Television

Impressive dedication to the task over a long period from John.

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Old 29th Nov 2020, 6:50 pm   #447
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Default Re: Fixing a GEC BT 302 Television

BT 302 (and 318) a pleasure to do. Sadly my 302 needs a rear cover, must get around to
that one.
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Old 29th Nov 2020, 7:47 pm   #448
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Default Re: Fixing a GEC BT 302 Television

3 Posts moved to new thread here:

https://www.vintage-radio.net/forum/...54#post1315654

Cheers

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Old 30th Nov 2020, 3:24 pm   #449
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Default Re: Fixing a GEC BT 302 Television

Now posted.
Take care when you fit them with special regard to the valve positions. Ask if your not sure. It's hard to get them mixed up if you take a look at the pictures I posted a couple of days ago.
Good luck and I'll keep a light burning in the porch. Regards, John.
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Old 1st Dec 2020, 8:54 pm   #450
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Default

The TV has a Raster, few loose wires soon cleared up a lot of things. With help of john I've managed to get it working.

Here are some pictures
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Old 1st Dec 2020, 9:30 pm   #451
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Default Re: Fixing a GEC BT 302 Television

Well at last it's a raster Darren. You mentioned that the frame output valve glowed blue on switch on and you fitted the spare one you had to hand. By the look of your picture it looks a bit low emission.
I will test up a decent one and forward it together with a couple of 30F5/Z329 valves to replace the two Z152/6BX6 valves that have been fitted some time in the distant past in place of the correct Z329/30F5 valves on the timebase panel. The Z152 and 6BX6 will work OK for now so leave the whole chassis alone until you find a signal source.

You're getting clicks and flashes on the screen when you rock the turret tuner positions. This goes a long way to prove that the tuner and I.F. stages are working.
98% complete. Regards, John.
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Old 1st Dec 2020, 9:36 pm   #452
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Default Re: Fixing a GEC BT 302 Television

Thanks again John I really appreciate it mate. I managed to fix the record player that,s in the second picture on the left, Great now tellys working
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Old 3rd Dec 2020, 7:22 pm   #453
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Default Re: Fixing a GEC BT 302 Television

Where can I buy a standards converter?
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Old 4th Dec 2020, 11:20 am   #454
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Default Re: Fixing a GEC BT 302 Television

Darren, you require what is known as a system A standards converter. There are two well known ones one of which has been around a long time, the AURORA. I believe these have now ceased production but from time to time they do turn up on the usual auction sites.
It is an excellent converter with a good reliability record.

The new boy on the block is the Hedgehog. Two versions have been produced, the Mk1 and the Mk2. Either will serve your purpose admirably. This is a brilliant successor to the Aurora giving excellent results.

The slight drawback is that they both cost around £185-£200 and if you have only one 405 receiver, it may be a lot to spend. They are both excellent value for money probably giving better results than the massive converters fitted at the transmitters in the late 60's and they cost many thousands of pounds back then.

Standards converters realize good prices on the second hand market and if you decide to sell one a considerable amount of it's cost can be recovered.

Do not confuse standards converters with digital set top boxes. Digital set top boxes are completely useless for displaying pictures on a 405 line receiver.

Just enter the words AURORA and HEDGEHOG into Google..

John.
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Old 4th Dec 2020, 3:52 pm   #455
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Default Re: Fixing a GEC BT 302 Television

I was reading this article:-

http://www.nostalgiatech.co.uk/240%20lines.htm

about using this to convert the 405 signal I have the parts but not the modulator. Will this work for the modulator:-

https://trade.vision-products.co.uk/...SB-240V-120009

Thanks
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Old 4th Dec 2020, 7:32 pm   #456
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Default Re: Fixing a GEC BT 302 Television

Darren, I don't think this is suitable for your requirements but there may be others that think differently.
To be perfectly honest I don't think you are experienced enough to cope with the problems that may be encountered.
You can talk about issues for ever but you may have problems with this and problems have to be solved.
I would suggest you keep an eye for someone disposing of their older Aurora. It would be the easiest and probably the cheapest way to solve this. John.
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Old 4th Dec 2020, 7:58 pm   #457
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Smile Re: Fixing a GEC BT 302 Television

Another vote for the Aurora. I have 2 now and very easy to use too. 625 line video in and sound in on phono sockets, and 405 line RF output on band I or band III with switchable channels. Just need the right wall wart to power it and a coax cable from the telly to the Aurora with an F connector on one end.

Also displays test card C when no video data is being received which is a big plus when you are setting the telly up to do some viewing.

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Old 4th Dec 2020, 9:07 pm   #458
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Default Re: Fixing a GEC BT 302 Television

They are both excellent. I have both Aurora and Hedgehog converters. The Hedgehog has very useful easy to access features and gives a first class picture. I am more than pleased with both of them. John.
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Old 5th Dec 2020, 7:41 pm   #459
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Default Re: Fixing a GEC BT 302 Television

Hello Darren, I only have experience with the Aurora, I bought mine in December 2008, it must have been one of the very first ones available.
It has worked very well with no problems in all that time.
It really is a first class product as several others have already stated.
Keep an eye on eBay as they do come up for sale from time to time.
Regards Alan
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Old 5th Dec 2020, 8:52 pm   #460
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Default Re: Fixing a GEC BT 302 Television

The Aurora also has a 405 composite video output so you can test monitors or feed to
other modulators. I can connect to the modulator of my old Domino converter - these
are also excellent but will only operate on a single channel (B1 or B4 as ordered).
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