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Old 20th May 2020, 12:01 pm   #361
deepspacedaz
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Default Re: Fixing a GEC BT 302 Television

I'll send some pictures now I m of to the electric shop today please let me know what I should get
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Old 20th May 2020, 12:32 pm   #362
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Default Re: Fixing a GEC BT 302 Television

Here we are
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Old 20th May 2020, 12:40 pm   #363
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Default Re: Fixing a GEC BT 302 Television

Daz, I'm loosing it a bit. Do you have a full screen or just the line? You seemed to imply that you now had an illuminated screen.
What is this line switch? Do you mean the control that you broke? Have you replaced it with the new one? Why are you going to the spares shop?
Until you answer these questions it will be impossible to continue.

The picture is what you are aiming to obtain. This is known as a screen raster. It's just a blank white screen that will respond to the brightness control.

Until you get somewhere near this we cannot get any further. What is the point in visiting your spares guy until you advise us of the position since you refitted the panel.
You cannot divert from the methodical steps taken in the right order. It's the only way we will get anywhere. Hope you understand where I'm going. John.
PS DAZ Our posts crossed.
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Old 20th May 2020, 12:44 pm   #364
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Default Re: Fixing a GEC BT 302 Television

No, I have not fitted the part as it's under 100k. Vert. The screen itself is brighter but still has the line
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Old 20th May 2020, 12:44 pm   #365
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Default Re: Fixing a GEC BT 302 Television

Nowhere near like yours
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Old 20th May 2020, 12:45 pm   #366
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Default Re: Fixing a GEC BT 302 Television

Did you get the pictures ?
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Old 20th May 2020, 1:07 pm   #367
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Default Re: Fixing a GEC BT 302 Television

OK. One good bit of news, Your tube looks good.
Your pictures show that the frame timebase is at last producing a scan. Congratulations!
The bad news is that it looks a bit weird. What effect do the height and frame form controls have on the raster?
My first thoughts are that you may still have one or maybe two capacitors fitted that are the incorrect value.
If your CERTAIN that they are all in place and correct [If not we will be led a merry dance]I would advise you to switch off and with your meter switched to the ohms range, measure the value of that resistor I mentioned that looked a bit overheated. It is R98. It's listed value is 300 ohms but this is a non standard value and can be replaced by a 330 ohm 2 watt. 1 watt will suffice if you can't get a 2 watt.
If you are going to your spares guy I would also suggest that you obtain a 220uf 63v electrolytic capacitor to replace C111 on your circuit. The resistor and capacitor form the cathode bias components and will have a serious effect on the shape of the raster, particularly the bottom of the screen. It is that large blue capacitor just below C113 when looking at the board from the component side.

On your circuit they are connected to pin 3 of the N379 [PL84] valve V15. The original value was 200uf. The modern replacement for this is the 220uf as mentioned earlier.

Now being an electrolytic capacitor it is Polarized. That means it is essential that you must connect this capacitor the correct way round. It will be clearly marked.
You mention that you have some intermittent cracking. Is this still happening? [I hope we get somewhere with this.] John.
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Old 20th May 2020, 1:09 pm   #368
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Default Re: Fixing a GEC BT 302 Television

Ill get the parts now
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Old 20th May 2020, 2:10 pm   #369
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Default Re: Fixing a GEC BT 302 Television

Daz, Before you fit any more parts, Can you answer my queries in my last post? failing this we are just going to start another long journey into the darkness. procedures... John.
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Old 20th May 2020, 2:31 pm   #370
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Default Re: Fixing a GEC BT 302 Television

Reluctant to chip in and maybe confuse matters but was the query on post 322 to 327 approx. (think it was for C116?) resolved satisfactorily?
I must say that I am in awe at the patience and helpfulness of those contributing, and the doggedness of the OP.
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Old 20th May 2020, 2:37 pm   #371
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Default Re: Fixing a GEC BT 302 Television

If St. Monica ever wanted to retire, I recon she would propose John as a replacement.
Dave
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Old 20th May 2020, 3:47 pm   #372
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Default Re: Fixing a GEC BT 302 Television

Quote:
Originally Posted by deepspacedaz View Post
No, I have not fitted the part as it's under 100k. Vert. The screen itself is brighter but still has the line
Yes, you need to fit that part, it's the vertical linearity potentiometer, also called vertical form pot, and I would expect exactly the fault you have shown with the damaged original.

You have done well to get to this point.
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Old 20th May 2020, 6:45 pm   #373
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Default Re: Fixing a GEC BT 302 Television

Agree! You will never get anywhere with a missing pot! You may have to carefully bend the legs on the new pot to fit the circuit board.
The pot is in the linearity feedback circuit. That corrects the vertical shape of the scan basically to make the test card circle a circle rather than an egg shape. If the circuit becomes open circuit, in your case a broken or missing pot the output stage goes mad and produces all manner of strange symptoms. I thought it looked a bit weird but I thought you had replaced it. No worries.
We will get there Daz. John.
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Old 20th May 2020, 6:49 pm   #374
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Default Re: Fixing a GEC BT 302 Television

Quote:
Originally Posted by deepspacedaz View Post
No, I have not fitted the part as it's under 100k. Vert.
Daz, I don't understand what you mean here. Have you actually got the part? If the guy you get your parts from can't supply I can send you one in the post.

If that is the case let me have your address details VIA PM. J.
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Old 20th May 2020, 7:30 pm   #375
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Default Re: Fixing a GEC BT 302 Television

Yes, I have the part its and just under 100k. today I purchased 1 100k but it's modern I may have to attach wires
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Old 20th May 2020, 7:32 pm   #376
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Default Re: Fixing a GEC BT 302 Television

I have the 330 resister I need. the only cap he had is 220uf,
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Old 20th May 2020, 7:39 pm   #377
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Default Re: Fixing a GEC BT 302 Television

That is what I suggested you purchase. Did you buy it? Have you got the 100k preset? John.
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Old 20th May 2020, 7:49 pm   #378
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Default Re: Fixing a GEC BT 302 Television

Yes I have it
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Old 20th May 2020, 8:07 pm   #379
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Default Re: Fixing a GEC BT 302 Television

Here is the cap. the old vert reads 52.0 ohms the new black one is 100 k
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Old 20th May 2020, 8:10 pm   #380
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Default Re: Fixing a GEC BT 302 Television

Here they are
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