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CTV National TC-261G poor frame linearity

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Doz
 Doz
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Does anyone have the service manual for this set? It's got a frame linearity fault, which has improved since I replaced C462, which had popped it's bottom off. I did find a snippet of the schematic Chris posted when Wayne was working on one, but it seems to bear little resemblance to the set I have in front of me.

 

Any clues? 

 

TIA,

 

Doz.

12997 TC261Glopt
IMG20240506104842
IMG20240506104826
 
Posted : 06/05/2024 9:57 am
Doz
 Doz
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after much messing about I found the culprit, it's a tant, very thermally unstable. The issue is, it's marked with three dots, a slanted T and 35v ... so what's the value? I've tried 4.7u which cause the oscillator to run super slow, and 0.47 (these are the only two values I have in 35V!) , which works, but leaves low height. It's marked C454 on the PCB 

 
Posted : 06/05/2024 12:16 pm
Doz
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After further investigations, the tant proved out at 1uF. Replacement made zero difference (I used to 0.47's in parrallel). Freezing and warming the area has proved the SCS , 3SF11 is causing the issue. It appears to be made from unobtainium

 
Posted : 06/05/2024 1:21 pm
Jayceebee
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BR101 or BRY39 might be possible replacement? Radiomusem shows the internals as a PNP and NPN transistor and NTE239 as an equivalent. I'm presuming your set is much different from the circuit as I don't see an SCS anywhere.

John.

 
Posted : 06/05/2024 3:25 pm
Doz
 Doz
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Hugely different from that schematic. Thanks for the suggestionsof BR101, or BRY39.. nothing to lose !

 
Posted : 07/05/2024 7:53 am
Doz
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Well, a new BRY39 went in, and it's no longer thermal. It's not right by any means. If I get the frame adjusted right at the bottom, I can't get enough height. Chris is finding out the rest of the 262 schematic, which seems correct bar a few component numbers here and there.

 
Posted : 11/05/2024 2:45 pm
Doz
 Doz
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After our erstwhile leader provided a better, if not entirely correct schematic, the HT to the field output stage was low, traced rapidly to an O/C capacitor, C456 (on the diagram) which is C463 on the set I have. Set the frame up, and sat down with the set on test , and a few minutes later , there's a few crackles on the sound, followed by no sound. A poke round the AD421D shows everything normal, but no output ... damn. I've ordered one.

 
Posted : 11/05/2024 4:13 pm
slidertogrid reacted
Doz
 Doz
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Incidentally, freezing and warming the new SCS made zero difference, even with C456 O/C .... a garden path fault.

 
Posted : 11/05/2024 4:15 pm
slidertogrid
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These were excellent sets, The place I first worked for when I left school had loads, they sold so many Nat-Pan products they won 'dealer of the year' (or something like that.) The Prize? A brand new van sign-written in Panasonic Decals! I left in '81 and had never seen a faulty one! 

 
Posted : 11/05/2024 4:31 pm
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