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Murphy BC6341B (T22A)

 
Colour Television
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 MurphyV310
(@murphyv310)
Posts: 453
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Hi.

Well the first CTV that I've looked at since the Decca CTV22 that I modded for 405 line NTSC and really the first CTV that I'm setting out to repair since I left the trade. CTV is really not my thing but it was given to me, its very clean so I thought I'd give it a bash.

The guy I got it from has unfortunately plugged it in and after a look about I did the same and was greeted with R49 & C19 on the line scan panel very much objecting, I don't have a sheet for the set so have asked for one from the library.

I'll update with progress and pictures in due course.

Kind Regards

 
Posted : 08/03/2023 1:53 pm
 Nuvistor
(@nuvistor)
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@murphyv310 

Just had a look at the circuit, it appears that 4C19 and 4R49 are part of the startup circuit for the line oscillator. The rising HT produces a voltage to start the Line Ocs which starts the Line output which then provides the 12volts to keep the oscillator working.

 

 
Posted : 08/03/2023 5:08 pm
 slidertogrid
(@slidertogrid)
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Wasn't there a resistor that gave trouble in that area? ISTR it was a strange value, 910 Ohms ?

Rich

 
Posted : 08/03/2023 6:35 pm
 MurphyV310
(@murphyv310)
Posts: 453
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Hi.

When I downloaded the manual it all came flooding back, must be about 40 years since I saw one of these. Indeed it is the start up circuit, the 10uf cap no doubt was leaky and the 100 ohm fusible went up in a puff of smoke, the cap was quite hot too. No damage to the TBA950 or the zener etc, the 930 ohm resistor is OK too. Will fire it back up tomorrow and see what transpires, the CRT is good.

 
Posted : 08/03/2023 7:03 pm
 Nuvistor
(@nuvistor)
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@murphyv310 

Are fusesble resistors still available? I always used the correct safety components in equipment but I admit to never delving into how the resistors were made to be fusible.

I repaired the T20 series chassis but can’t recall the T22 series, on the other hand I have forgotten so much of what repairs I did 40-50 and more years ago.

 

 
Posted : 09/03/2023 1:31 pm
 crustytv
(@crustytv)
Posts: 12227
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Posted by: @nuvistor
↑

Are fusesble resistors still available?

Apologies for butting in, but the answer to that is yes.

Although finding the exact value may prove a chore, you'll likely have to adjust the value a tad, but that should not impact the cct. I had a similar problem at the end of last year when I was repairing a 1986 20" Ferguson, which decided to have a bonfire. In my case, a 33R fusible flameproof resistor, I did find 47R fusible flameproof on RS and that worked perfectly well. So RS is a good place to look.

https://www.radios-tv.co.uk/community/colour-television/1985-1986-ferguson-tx-20e2-tx90-chassis/

 
Posted : 09/03/2023 1:37 pm
Nuvistor reacted
 Nuvistor
(@nuvistor)
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@crustytv 

Hi Chris,

I remember that thread now, memory like a sieve.

 
Posted : 09/03/2023 1:53 pm
 neil1974
(@neil1974)
Posts: 616
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Hi Trevor.  If you're stuck for parts i might be able to help cause i've got a few (scrap) boards that can be used to supply most of whats needed and even a lopt if necessary.

Cheers

Neil.

 
Posted : 09/03/2023 5:21 pm
 MurphyV310
(@murphyv310)
Posts: 453
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Topic starter
 

Thanks Chris, Frank & Neil. All points noted and if I need anything I'll give you a call Neil, I used to have your phone number but not so sure if I still do.

Regards 

 
Posted : 09/03/2023 7:13 pm
 Till Eulenspiegel
(@till)
Posts: 4927
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The Rank T22 employed an improved decoder circuit. The sub-carrier frequency was 2fsc, 8.66Mhz. The X2 sub-carrier frequency simplified the 90 degree sub-carrier phase difference between the R - Y and B - Y signals. No coils to adjust.

The 910ohm resistor in the start-up circuit was often replaced by a 1Kohm resistor, although 1K and parallel 10K resistors is better.  To find if the start up circuit had failed a PP3 battery was used to supply power to the line oscillator. 

The new decoder was used in the 30AX T26 chassis. Very few were made because Rank Radio International ceased TV production in 1980.  Toshiba took over the Ennesettle factory. 

 
Posted : 09/03/2023 10:23 pm
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