Colour on Composite video mod for BBC model B

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cjed
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Colour on Composite video mod for BBC model B

Post by cjed »

I'm in the process of getting my old BBC Model B up and running. Done the usual PSU caps, and have added sideways RAM and EEPROM and a SD card / MMFS to go along with the original DFS.

I've just tried to enable colour on the composite video output (monochrome is working fine) by putting a link in S39. Doing this results in no video at all!

It's a Version 4 board, any ideas as to what might be wrong ?
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acorndave
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Re: Colour on Composite video mod for BBC model B

Post by acorndave »

Is there a 470pf cap at C58 ?

Apparently sometimes this is already there. Sometimes not, so you may have to fit it

http://www.8bs.com/hints/202.txt
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cjed
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Re: Colour on Composite video mod for BBC model B

Post by cjed »

Yes, cap C58 is fitted. It's odd that the composite signal just disappears when I make the link. I could understand it not adding colour, but it actually seems to kill the composite video. I'll try adding an external cap between the emitter of Q9 and the base of Q7 and see if that works.
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