[Coco] Coco SDC troubleshooting: no ROM found

[Zippster]

Hi Richard,

Definitely sounds like a contact problem.

How did you clean the flux off of the bard after
you built it? (if you did)

Likely some flux or other residue interfering.

Try taking a Q-tip soaked in isopropyl alcohol (91%) and clean
all the contacts in the PLCC sockets, as well as the card edge
connector and re-seat the chips.

- Ed



> On Nov 28, 2014, at 12:36 AM, Richard Goedeken <Richard at fascinationsoftware.com> 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.
> 
> I already did quite a bit of troubleshooting.  I swapped all of the chips out
> between the malfunctioning unit and a working one.  And after swapping each
> chip, the malfunctioning unit still malfunctioned, and the working unit still
> worked.  So it's not a problem with the chips.  I examined all of the solder
> joints with a 45x loupe and even went through and re-melted all of them and
> touched them up, but still no joy.  The DIP switches are all set to off.  I
> used a meter to 'ring out' the contacts on the flash ROM socket, and I got
> continuity on all of them.  I also tested the pins of the DIP switch, and they
> are definitely all not conducting.
> 
> So I'm sort of at a loss as to what could be causing this.  A bad socket?  A
> defect in the PCB itself; bad via maybe?  Can anyone suggest how to
> troubleshoot this further?  Maybe I can do some PEEKs to see if the SDC-DOS
> rom image is visible?  What else could cause it not to start up with the ROM
> extension?
> 
> Thanks,
> Richard
> 
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