[Coco] Coco SDC troubleshooting: no ROM found

[Richard Goedeken]

Thanks for the tips, to everyone who replied.  After more troubleshooting, I
found that one of the pins on the PLCC32 socket for the flash rom chip was
bent, and it was short-circuiting against the pin next to it.  This had the
unfortunate effect of grounding D2.  After straightening the pin and
reinstalling the flash chip, it works great!

Thanks,
Richard

On 11/28/2014 07:26 AM, Darren A wrote:
> 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
>