[Coco] Coco SDC troubleshooting: no ROM found

[Brett Gordon]

I had a very similar problem after inserting my SDC into a CoCo2.
Maybe my female card-edge on the CoCo is dirty.  After I replugged it
into my coco3 same problem.  I played with the DIP a bit and spent 1/2
hour plugging and replugging it in and it started working again...

On Fri, Nov 28, 2014 at 9:38 AM, Zippster <zippster278 at gmail.com> wrote:
> 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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>
>
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-- 
Brett M. Gordon,
beretta42 at gmail.com