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Old 10th Jun 2006, 10:38 am   #4
oldeurope
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Join Date: Dec 2003
Location: Solingen, Germany
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Default Re: FOTH RGB combiner problems

Hi Kat,
thanks for your schematic.
Your problem is two transistors Q8 and Q11 are going to saturation.
This makes the pulses longer.
Are you sure with D1 and Q6 ?
I don't know the voltage of the black level, but it seems possible
to feed the sync from pin8 via a resistor to emitter of Q7.
In this case you don't need R23 R28 R29 Q8 Q11 and R17 is 100 Ohms.
(higher bandwidth!)
For serration pulses a solution with fH x 10 and a modulo counter is
independent from the standart. But the fH x 2 and monostables works fine
too.

Kind regards
Darius

Reason for editing: I didn't see the minus 5V, I thaught it is ground
this negative voltage rail makes it complicated . Speedup your transistors Q8 and Q11
with a schottky speedup Diode BAT46.
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