[Coco] Coco SDC troubleshooting: no ROM found

[Darren A]

On Thu, Nov 27, 2014 at 11:36 PM, Richard Goedeken wrote:

> Hello everyone,
>
> Today I built up two CocoSDCs from kits, and one of them works perfectly
> but
> the other does not.  If anyone could help me get my second unit working I'd
> much appreciate it.
>
> The non-working unit doesn't boot up with the SDC-DOS extensions.  It just
> boots as Extended Color Basic 2.0 or whatever the default Coco3 basic ROM
> is.
>  The LED will light up and stay lit if there's no SDHC card inserted at
> power
> up.  If there is a card plugged in however, the LED will light for a
> second or
> so after power-on, and then it will turn off.  It flashes if I hit reset.
> So
> some portions of the system are working.  But for some reason the Coco
> doesn't
> start up the SDC-DOS rom extension, so it is not usable.
>

<snip>

Richard,

You may want to PEEK the first few locations starting at $C000 (49152). The
first two bytes of the ROM image should be the ASCII characters 'DK'. If
one or more of the data lines has a contact problem then this may reveal it.

There is a schematic available for download from the blog site. You could
check for CE* and OE* continuity between the pins of the CPLD and Flash
chips along with the bank addressing lines.

Darren