[Coco] CoCo 3 to RBG...

[gene heskett]

On Thursday, July 21, 2011 05:31:13 PM Mark Ormond did opine:

> Ok, this is still that old gbs-8200 series converter that we are talking
> about right?
> 
> If so, could you post the schematic of the sync combiner/inverter? I
> usually just throw a 7404 with a cap on it to get a self powered sync
> inverter (Old arcade game trick), then what are you doing to combine
> the sync correctly?
> 
> Here is the link to the arcade style self powered sync inverter/combiner
> circuit. It uses a single 7404 , 2 diodes and a 20uf cap.
> 
> http://www.mikesarcade.com/wiretap/info/SyncInv.pdf
> 
This one is going to fight with itself, using up lots of the feeble power 
because the first 2 gates outputs are paralleled.  This should be used only 
in an open collector circuit, effectively making a NAND gate out of it.  
The 74C04 has active pullups.  There is not enough power available to 
destroy the chip unless it has external power instead of the self powered 
setup now.
 
[...]> 
> I'd still like to ask these folks what polarity of sync signal it
> expects. Right now, we are feed it positive polarity, and IIRC the
> normal convention is negative.

I sent them a message via their web page, but have not heard back.

Cheers, gene
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