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Old 14th Jul 2010, 9:51 pm   #61
murphyv310
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Default Re: GEC BT1156 First Light & Vidor CN4216

dobrĂ½ den, Chris
I will have a look for the circuit tomorrow night and have a look at the line osc, and see what components do the timing of the oscillator, one other thing to check is that the sync coupling from the sync seperator to the line osc comonents are ok, don't ask me what they are as I have locked up the shed for the night but I will post all the info tomorrow night (unless you have fixed it beforehand).
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Old 14th Jul 2010, 9:54 pm   #62
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Default Re: GEC BT1156 First Light & Vidor CN4216

Hi Chris,
if you measure at the "other" end of R131... the end away from the 0.5 uF capacitor... that point is the boost rail itself and you will get a more accurate reading of the boost voltage, without any reduction due to the meter current flowing through the 2.2meg resistor.
Depending on the meter you are using this could be a lot or a little.
Pete
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Old 14th Jul 2010, 10:02 pm   #63
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Default Re: GEC BT1156 First Light & Vidor CN4216

Pete
Don't forget that boost volts are in relation to line speed, so if the volts are wrong Chris may look for a Boost fault when in fact he doesn't actually have a boost fault.
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Old 14th Jul 2010, 10:04 pm   #64
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Default Re: GEC BT1156 First Light & Vidor CN4216

Hi Pete

R131 measures 2.7M not 2.2M but that would seem to be within the 20% tollerance. Voltage on other end "Boost Rail" is 395V

I cannot for the life of me find the boost cap, perhaps it's tired eye syndrome setting in again.

I'm in the process of checking resistors in the line osc stage but I guess some have to be checked snipped as they give spurious reading, oh how I loath the PCB style conections, give me good ole hard wiring any day.
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Old 14th Jul 2010, 10:12 pm   #65
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Default Re: GEC BT1156 First Light & Vidor CN4216

G-day Chris.
Dont worry about boost volts at this point, you need to get a properly locked picture first, the reason I say this is simple, the line stage of a 405 line tv (line tranny, scan coils and oscillator components) are designed to operate at 10125 HZ not at a different frequency so any change (1KHZ above or below or more) will cause a change in boost volts, reduced height, changes to width and even failure of the line tranny, so try to ge the set locked up first then and only then if the boost is incorrect investigate it.
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Old 14th Jul 2010, 10:15 pm   #66
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Default Re: GEC BT1156 First Light & Vidor CN4216

For tonight I shall call it quits

I had a look at R114 according to the circuit it should have 100V and it only has mA
C110 should have 72V and that has 103V.

Cheers to all

Edit:
Thanks for excellent explanation Trevor, I will hang up the probes for the night one thing I learnt from the V4 marathon was knowing when to quit. I will hav a wander through some other posts

Chris
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Old 14th Jul 2010, 10:18 pm   #67
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Default Re: GEC BT1156 First Light & Vidor CN4216

Nite nite.
No dreaming about tellies!!!
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Old 14th Jul 2010, 10:20 pm   #68
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Default Re: GEC BT1156 First Light & Vidor CN4216

If only that was not so true
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Old 14th Jul 2010, 10:25 pm   #69
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Default Re: GEC BT1156 First Light & Vidor CN4216

Hi Chris , The boost capacitor C131 ( 0.05 uf ) is mounted on the small paxolin board in front of the LOPT just to the rear of the horizontal form & width coils , Chris..
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Old 14th Jul 2010, 10:28 pm   #70
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Default Re: GEC BT1156 First Light & Vidor CN4216

Hi Trevor,
yes, I know where you're coming from, and as it happens the readings confirm the boost volts really is a bit low.
So it's definitely time to concentrate on getting a locked timebase at 10.125kHz and see what happens then.

Seeing as someone else has already re-capped the set it could be worth double checking the values actually fitted in the line oscillator against those in the diagram... just in case it's another man made fault.
TTFN
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Old 14th Jul 2010, 10:31 pm   #71
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Default Re: GEC BT1156 First Light & Vidor CN4216

Splutters out of sleep shouting "BOOOOOST"


Hi Chris
I looked at that and dismissed it because the new in cap in place is a 0.1 not a 0.05 so that's the wrong value

Chris

Edit:
Pete MMF for sure, I was gutted when I opened this set and found the recapping, I thought It was going to be a turn on and watch, how wrong and perversly how much fun
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Old 14th Jul 2010, 11:05 pm   #72
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Default Re: GEC BT1156 First Light & Vidor CN4216

Annyeonghaseyo? Cris,
Assuming that the line oscillator valve is OK, then the the components that determine the frequency must be checked. C109 (200pF) is a mica component and is normally reliable, but after more than fifty years it could well be faulty. R112 is only 1Kohm, it goes to the slider of the line hold control via R65 330Kohm. R65 and R69 are liable to go high in value which would cause the line fequency to go low. Check the line hold pot and resistors R67 and R70. The sawtooth waveform is developed across C112. This part should not set the frequency, but check it anyway. I hope the line blocking transformer is OK. The fact the anode volts of V14 is still high at 100V I think you might well still have a faulty valve.

It's getting late so I'm out of here.

David.
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Old 15th Jul 2010, 7:45 am   #73
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Default Re: GEC BT1156 First Light & Vidor CN4216

Hi.
The actual value of the boost cap isn't all that critical, a 0.1 instead of a 0.05uf will be OK.
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Old 15th Jul 2010, 12:02 pm   #74
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Default Re: GEC BT1156 First Light & Vidor CN4216

Update:

I have been measuring around the Line TMB circuit and the Frame TMB

so far all the following are within 20%
R67, R68, R69, R70, R112, R113, R116, R117, R131

I have also replaced V14 & V13 for NOS.

The quest continues.

Chris
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Waarom oh waarom kan ik niet vinden de route van deze fout
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Old 15th Jul 2010, 12:15 pm   #75
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Default Re: GEC BT1156 First Light & Vidor CN4216

Can you put up this part of the circuit. Help us all.

Don't know much Dutch I'm afraid, but.... ee by gum eck'a'my thump an were's tha whippet?

Cheers,

Steve P.
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Old 15th Jul 2010, 12:16 pm   #76
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Default Re: GEC BT1156 First Light & Vidor CN4216

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Old 15th Jul 2010, 12:51 pm   #77
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Default Re: GEC BT1156 First Light & Vidor CN4216

First, V13 is sound only and won't make that much difference. Ignore anything connected to it.

If V14 is OK, then the capacitors to change are C110 (Look at a radio chassis and you'll see that it is the TV equivalent of THAT capacitor), C108 and C112.

The pins 3.1.6 and 9 all go to earth. Check them.

R112 goes somewhere via Pin 33. Check the resistor and wherever it goes to.

Cheers,

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Old 15th Jul 2010, 12:58 pm   #78
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Default Re: GEC BT1156 First Light & Vidor CN4216

Hi Steve,

C110 is a new yellow 630V axial, and is a pain to remove, can I not verify any other way first before having to remove what's probably going to be an ok cap.
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Old 15th Jul 2010, 1:02 pm   #79
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Default Re: GEC BT1156 First Light & Vidor CN4216

Scope both ends of it. Like that capacitor does on a radio, it should block DC.

Where do pins 33 and 34 go from the timebase panel?

Cheers,

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Old 15th Jul 2010, 1:09 pm   #80
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Default Re: GEC BT1156 First Light & Vidor CN4216

Hi Chris,
the lead from tag 33 will be going to the line hold pot. There will probably be resistors associated at the top and bottom of the pot, so check these for value as well as checking the end to end resistance of the pot itself.
Pete
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