[Coco] Strangely patched CoCo 1

[Bruce W. Calkins]

The early "F" boards did have a timing problem that resulted in a lockup.
There was kludge hardware fix for them that may be what is described.  In my
experience, NO amount of cooling or part swapping could cure the unpatched
board.  The hardware patch for problem units was discontinued shortly after
the corrected board dominated the market.

Bruce W.



> I think there is a good chance it is the part described in the Tandy Tech
> Bulletin CC:20. The part is 26-3003B logic board AX-7089 which has an
> SN74LS12 and SN74LS393. I don't have a schematic but if the above is your
> part, it is designed to correct a timing problem which caused a hardware
> crash after about 30 minutes of use. It was a heat related problem that
> could be corrected by adding heat sinks and drilling air holes in the case
> without the need of the kit.
>
> Phill Harvey-Smith wrote:
> > Hi all,
> >
> > Just got a second CoCo 1 off ebay (26-3002) and it has a strange little
> > patch board inside that my other does not (26-3004). The board is
> > mounted upside down next to the SAM, and has about 5 or 6 wires going to
> > various places on the CoCo board. Also one of the other chips, has had a
> > couple of it's legs lifted and a disc cap & inductor soldered to them.
> >
> > I know these where factory fitted because the waranty seal had not been
> > broken.
> >
> > I am in the UK, and this is a UK machine, the one thing that did cross
> > my mind that perhaps the mainboard is a US/NTSC, and the patches have
> > been made to convert the machine to run on the UK/PAL system.
> >
> > Can anyone comfirm this and does anyone have a schematic for it ?
> >
> > Cheers,
> >
> > Phill.