[Coco] CoCo 3 to RBG...

[Mark Ormond]

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




-----Original Message-----
From: coco-bounces at maltedmedia.com [mailto:coco-bounces at maltedmedia.com] On Behalf Of gene heskett
Sent: Thursday, July 21, 2011 12:38 PM
To: coco at maltedmedia.com
Subject: Re: [Coco] CoCo 3 to RBG...

On Thursday, July 21, 2011 12:25:28 PM Steve Batson did opine:

> No kidding about this getting more confusing as we go. At first, when I
> didn't get mine working after the first pass, I figured I probably have
> a bad connection or didn't wire it right. And I haven't had a chance to
> get back and double check my connections to make sure everything is
> correct. With the other people here having issues, I know it's not just
> me ;)
> 
> Seems pretty straight forward when you look at the connectors on this
> board and the CoCo. If the CoCo is not putting out the proper
> signals/levels for this board, then it's not standard RGB I would
> think...but it works with the CM8 as well as a Magnavox RGB monitor, so
> I'm suspecting it is a Standard RGB output requiring just the proper
> cable to go to the monitor.
> 
> That said, I'm more inclined to think that the board is the issue and
> meeting it's requirments is not as obvious as it should be...and the
> skimpy manual doesn't help matters. My electronics background doesn't
> include much video, so while I can follow much of what's been said in
> this thread, I'm not in a position confirm or deny anything that's been
> said. I am going to keep toying with my setup to see if I can get it
> working, but I'm also anxious to see what others here find out.
 
I don't have the chip on hand to do it, and would have to mail order it, 
but I am inclined to setup a double inverting buffer for both sync sigs, 
and try both polarities.  When I get my drive 0 sorted, I'll get back to 
this, which may be yet today as I know there is one good drive in the EDISK 
kit yet, and possibly in the drive package of my old office machine too.  I 
just have to clear off my adjacent reloading bench so I can use it for a 
work table.  It currently has my electronic powder scale all over it as I 
am changing the design somewhat.  The inputs for sync on the 8 pin 
connector do not appear to be video terminated, reading about 750 ohms for 
either polarity of the meter for H sync (grey wire) and about 1400 ohms for 
the V sync, yellow wire, so available drive power from the coco's IC15 
buffers shouldn't be a problem.

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.

Cheers, gene
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