Fixing a GEC BT 302 Television

[Heatercathodeshort]

Originally Posted by deepspacedaz

Thats the Badger, sorry

Have you got a pet Badger? If you have, give him the soldering iron and let him have a go!

But seriously Darren,

No need to send pictures at the moment. Just make sure that the soldering is correct where we queried the possible short in the top right of the printed side of the board.

John.

[deepspacedaz]

Ok ill check it overr

[deepspacedaz]

Hello and good morning

[deepspacedaz]

Parts are here I'm ready

so I'm i soldering the new ones in now

[Heatercathodeshort]

Before you switch it on. Please read these notes Darren.


You need to carry out a few basic checks before you get involved with the acquisition of a signal source.
I have posted pictures that will give a reasonable indication of what you would expect to observe with a good frame timebase.
Before you switch on for the check, set the height R104 and form control R96 in the same positions as the picture. These are my settings and will give a rough position of the presets. The preset 'slider' R97 at the top of the board adjusts for small errors and can be ignored at this stage. Set it as the picture and adjust the vertical hold control midway.
The first one shows what a blank raster should look like. Note that the scanning lines are the same distance apart at the top and bottom of the raster. You may be able to see this easier if you reduce the height a little to give a black bar top and bottom.
If the scanning lines at the top or bottom are 'cramped up' you need to adjust the FORM control in an attempt to correct this. Little more can be done test wise without a signal but if the above appears to bring it into line, leave it well alone for now.
With the full raster on the screen rotate the channel selector knob between channels and see if you get flashes on the screen. The positions with no flashes will not contain any channel coils and can be ignored. The BT302 was usually supplied with pairs of coils known as 'biscuits' for the following channels: 1-2-3-4-5-8-9-10. They may not all be included but your flashes on the screen will indicate the positions that are fitted with coils.
These rather basic tests will confirm that a signal of sorts is getting from the tuner, through the I.F. stages and video amplifier to the CRT itself.
Don't worry about the sound. It should be a doddle to fault trace once you get a signal.
These simple tests can be carried out without an aerial and should indicate the progress so far.
The pictures show:
A plain white raster as it should appear.
The raster with the height control reduced slightly showing the scanning lines stretched at the top and cramped at the bottom.
The raster after adjusting the frame form control to equalize the spacing of the scanning lines.
IF everything appears OK. We can continue with the easy bits.... John.

[deepspacedaz]

So do i need to add the two new ones I thought only one was broke ?

[Graham G3ZVT]

Originally Posted by deepspacedaz

So do i need to add the two new ones I thought only one was broke ?

If you mean the presets, then only the "vertical form" needs changing at this point. We will find out in due course what else is faulty.

[deepspacedaz]

Ok thanks Ill do it now

[deepspacedaz]

Ok ive done that

[deepspacedaz]

This what I have now

[deepspacedaz]

we have lots of smoke from the tuner side that looks like a resistor. I can see all liquid

[Heatercathodeshort]

Ok.. So what effect has the height and form controls have on the display? See my post 406. Does the height control have any effect? Can you open it up?
Unless you make some adjustments and make a note of what the controls do, we don't have enough information to work with.
Have you fitted the replacement valves I sent you? They are chassis tested and I know they work 100%. J.

[Heatercathodeshort]

You have the GEC manual with all the components clearly marked on the printed panel layouts. What is the number of the component that has overheated? It can't be a resistor due to the 'liquid'.

[deepspacedaz]

Comp C82 Has blown

[deepspacedaz]

Ive not fitted the new valves the height has a little effect no scan lines

[Heatercathodeshort]

C82 is a .001uf capacitor, probably a disc ceramic. [It's a heater decoupler.] They produce very little if any smoke when they fail and don't contain any liquid but if you are sure it is the cause of the smoke, disconnect it. It's a very small component and the 302 will work without it and can be replaced later.
As far as the height problem, I would suggest you fit both valves I sent you and if there is no improvement it can only be down to two things.
Either you have a wrong value capacitor fitted or a solder splash has shorted a couple of the printed tracks.
Failing that I think we have just about covered everything that can be done at a distance. John.

[deepspacedaz]

Here you can see it leaked looked like where smoke came from

[deepspacedaz]

That stuff is near the resister

[19Seventy7]

It looks like hot wax.

Have any capacitors or resistors changed appearance?

[deepspacedaz]

Only the one in the picture