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Old 15th Jul 2010, 9:02 pm   #101
MALC SCOTT
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Default Re: GEC BT1156 First Light & Vidor CN4216

Change that selenium rectifier. Chek the ht volts before and after.
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Old 15th Jul 2010, 9:05 pm   #102
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Default Re: GEC BT1156 First Light & Vidor CN4216

Chris...just an observation. You might want to use an alternative type of resistor in the heater of the EHT reccy. Remember that resistor is at EHT potential. Those blobs on the lead terminations may be OK this weather but come the cold and damp, you may get some corona and arcing. Best to use a carbon type of about 1 watt.



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Old 15th Jul 2010, 9:31 pm   #103
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Default Re: GEC BT1156 First Light & Vidor CN4216

Hi, Well its been 2+ hours and the set is running fine, picture is stable, I managed to find the width controls. Calling it quits for tonight and will be back at the bench tomorow and try to get the HT & EHT up to the correct levels.

Hi Malc,

Yep going to give that a try in the morning, I've created a clip in affair I will try (see pic)

Hi Rich,

Thanks for the tip, that's all I had to hand I will try and order up a 1W 5R then.

Cheers
Chris
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Old 15th Jul 2010, 9:43 pm   #104
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Default Re: GEC BT1156 First Light & Vidor CN4216

Find the Height control too while you're at it. Bring the picture out too.

Then it looks like you're almost there!

Cheers,

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Old 15th Jul 2010, 9:52 pm   #105
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Default Re: GEC BT1156 First Light & Vidor CN4216

That's it Steve, max I can get, I found the vertical form and I assume the reduced height and width is due to low HT and EHT, i'm down about 5KV
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Old 15th Jul 2010, 10:01 pm   #106
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Default Re: GEC BT1156 First Light & Vidor CN4216

Put up the Frame stages.

Cheers,

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Old 15th Jul 2010, 10:12 pm   #107
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Default Re: GEC BT1156 First Light & Vidor CN4216

http://www.oldticktocks.co.uk/GECFRMTMB.jpg
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Old 15th Jul 2010, 10:17 pm   #108
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Default Re: GEC BT1156 First Light & Vidor CN4216

OK. Height control is R90.

If V12 is OK, then I would go for R89, R91, C98 and R93.

Also R85.

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Old 15th Jul 2010, 10:24 pm   #109
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Default Re: GEC BT1156 First Light & Vidor CN4216

R90, is this crappy little mica affair and it has no effect, looks like someone has had it out in the past too. Why did GEC not use a nice proper control like the Hoz/ver & brightness..grrrrr
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Old 15th Jul 2010, 10:33 pm   #110
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Default Re: GEC BT1156 First Light & Vidor CN4216

Price probably. If it's having no effect then the problem is round here.

Cheers,

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Old 15th Jul 2010, 10:44 pm   #111
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Default Re: GEC BT1156 First Light & Vidor CN4216

Having a closer look at the back, the first leg is loose. I inserted some tweezers and found that the copper track could be lifted from the board for the first 3mm, it's still intact with the rest of the track so no breaks.

However the first leg is not soldered well and I found I could lift the track up and away from the leg. I have now gently put the track back over the leg and I guess I can solder it. The second two legs look a mess like one mass solder blob.

As I've said before it's a personal thing but i loath this PCB type affair, I like hard wired. Is there anyway I coul dremove this mount and hard wire it in?

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Old 15th Jul 2010, 10:49 pm   #112
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Default Re: GEC BT1156 First Light & Vidor CN4216

If R90 has no effect it's likely the wiper is open circuit... not contacting the track perhaps or even dodgy soldering to the pcb.
The linearity looks reasonable, so the fault is very likely to be in this series chain.

By the way, R70 can be either disconnected or connected to centralise the horiz hold within its range. It looks to me as though it could be worth experimenting with it in and out of circuit if yours is still at one end.. It's there to take up variations in valve and component tolerances.

You can replace the height pot with a standard 1 meg linear pot wired to the pcb but you'll have to find somewhere to mount it. That's probably another reason the makers used a skeleton preset part soldered to the pcb. You will only need to run two wires, one to the wiper (middle pin) and one outer pin, other to the remaining outer pin.
Pete

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Old 15th Jul 2010, 10:57 pm   #113
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Default Re: GEC BT1156 First Light & Vidor CN4216

Remove the solder.
Take out the pot and check it thoroughly. Make sure it's OK.
Remove any loose tracks.
Get some thick wire. Use it to replace the tracks.
Solder the pot to the thick wire.
Set it midway.
Check your work against the manual and the set,
Switch on.

Cheers,

Steve P.
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Old 15th Jul 2010, 11:09 pm   #114
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Default Re: GEC BT1156 First Light & Vidor CN4216

Another quick tip, Chris
don't use solder to bridge broken tracks on the pcb. A lot did, and it almost always end in tears with ropey pcb's, even if that's at a later date.
Use tinned copper wire or, for long links, insulated link wire (this is industrial good practice, we use PTFE insulated) and in any case take the ends back to a component lead where you will be able to make a better joint with less stress on the track itself and its tenuous bond to the board.

GEC pcb's were (in)famous for tracks coming away if you apply too much heat or for too long.
HTH

Pete
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Old 16th Jul 2010, 10:06 am   #115
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Default Re: GEC BT1156 First Light & Vidor CN4216

Morning all,

Looking for some opinions to a proposal I have regarding the duff R90

I've decided that I really don't want to faff about with the original flimsy unit or go messing with the PCB tracks.

My idea is:-

Fit a 1M pot into the chassis and hard wire fly leads to the components. I have found an excellent location but I'm a bit unsure of the fine points. I know the pot should connect to one end of R89 a 470K and the other end one end of R91 and do I use one outer and the centre of the pot, I could use some help here.

I've tested the pot and it measures 0R - 1.1M
I have fitted into location to see if it is viable and access can be met, which it can.

Chris
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Old 16th Jul 2010, 10:24 am   #116
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Default Re: GEC BT1156 First Light & Vidor CN4216

R89 to one end of the pot. Either, does not matter.
R91 to the middle of the pot.
Leave the other pin of the pot.
Insulate it properly.

You're using it as a rheostat rather than a potentiometer.

Cheers,

Steve P.
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Old 16th Jul 2010, 11:33 am   #117
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Default Re: GEC BT1156 First Light & Vidor CN4216

I've mounted the 1M Rheostat and have insulated the shaft, I changed my mind on the little knob fitting a BIG one so all you have to do is put one finger on it and rotate, saves getting whole hand in.

Finally I fitted a insulation plate to shield the connections. Is this adequate insulation.

On the insulation plate I will use an indelible marker and detail the mod and why.

Chris
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Old 16th Jul 2010, 11:50 am   #118
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Default Re: GEC BT1156 First Light & Vidor CN4216

Fine that. But the important thing is does it work...

Cheers,

Steve P.
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Old 16th Jul 2010, 11:57 am   #119
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Default Re: GEC BT1156 First Light & Vidor CN4216

working on that now, I take it I can just leave the old duffer in place
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Old 16th Jul 2010, 12:05 pm   #120
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Default Re: GEC BT1156 First Light & Vidor CN4216

Whip it out. Better safe than sorry.

Cheers,

Steve P.
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