[Coco] [Color Computer] COCO II A/V Mod

[Fedor Steeman]

Hi!

I actually have some old documentation for doing precisely that that I
wanted to scan in, translate from Dutch and post online for a long time but
never got around to do it. I can revive the effort if you're interested!
Just let me know...

I also have a CoCo2 that has that mod with composite video output, but it
no longer works (probably some short circuit). If you search the CoCo
mailing list for my name and the proper keywords you may find this earlier
discussion.

Cheers,

Fedor Steeman


On 26 May 2012 06:21, Computer Doc <computerdoc at sc.rr.com> wrote:

> Double check to make sure both transistors are functioning correctly.  I
> need some HP oscilloscope probes, so I can't verify your 20mV measurement,
> but if you have the correct DC voltage on each transistor pin minus the
> voltage drop across each transistor junction then your circuit should work.
> It seems like I remember output video rms voltage is very small like 1V
> peek-to-peek.  Video Circuits are not my forte but a close friend of mine
> has taught me quite a bit over the decades.  It would seem to me that 20mVs
> is just too small to effectively produce a good video image on a composite
> video monitor if any at all.  Also make sure that you soldered the color
> monitor driver circuit to the correct pins of the MC1372 IC.  The following
> is another link (the original I can't find) of the same simple color
> monitor
> driver circuit that produces a composite video output for the color
> computer
> that I used.  When I built it, mine would not work either.  I got to
> checking DC voltages to make sure the transistors were turned on and it
> turned out that the final NPN was not turned on!?!.  I suspected Radio
> Shack
> must have sold me a bag full of NPNs that must have had some PNPs mixed in
> with them.  It turned out that MOST (12 out of 15!) transistors in the bag
> was PNPs!  It was labeled NPNs!  I got the transistors switched out, but I
> have not gotten back to replacing the PNP with an NPN yet.  It's so simple
> I
> should have done it already, but I have been busy building a Motorola
> 6802/6846 microprocessor & ROM, I/O, Timer based computer system that I had
> started way back in college. I never finished it because the project was
> too
> overwhelming and I did not have enough time to complete it. I've been
> reinspired to tinker with 8-bit microprocessors again and I just have not
> gotten back to repairing my composite video driver circuit.  I have my
> color
> monitor driver circuit  connected to my Coco 2 also.  I pray you find the
> problem so you can enjoy your Coco 2 also.  Happy Computing!
>
> Kip Koon
>
> Here's the link:
> http://coco_docs.tripod.com/id53.htm
>
>
> -----Original Message-----
> From: coco-bounces at maltedmedia.com [mailto:coco-bounces at maltedmedia.com]
> On
> Behalf Of Ale Smukler
> Sent: Friday, May 25, 2012 9:40 AM
> To: ColorComputer at yahoogroups.com
> Subject: [Coco] [Color Computer] COCO II A/V Mod
>
> Hi! I'm an argentine Home Computers collector and am interested in adding a
> audio / video composite outputs to a COCO II (my model is a "melted
> keyboard" one). I saw that there exists a circuit, but I can't find it!.
> Could you help me, please?
>
> Muchas gracias!
>
>
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