[Coco] Broken CC3
georgeramsower at gmail.com
Fri Sep 12 10:19:45 EDT 2008
> On Friday 12 September 2008, George Ramsower wrote:
>>----- Original Message -----
>>From: "Gene Heskett"
>>> On Friday 12 September 2008, George Ramsower wrote:
>>>> My CNC coco broke.
>>>> It starts up and displays the usual stuff. I can ?mem and it reports
>>>>correctly. However, when I boot OS9, it crashes.
>>>> I appears to crash when it loads the first boot sector.
>>>>I tried other boot disks with the same results.
>>>>I replaced the CPU, RAM board, reseated the GIME, polished the edge
>>>>connector on the disk controller, reseated the ROM in the controller
>>>>all gives the same results.
>>> This smells like a memory problem as os9 put it in all ram mode.
>>> there is a problem with the memory above 32k?
>> This is why I replaced the memory board from another coco. I was thinking
>>the same thing.
>> The re-seating of things was the first step, then the memory, then the
>> I think the next thing to try is another GIME chip. I've never had one
>> I think I'll try that now and see.
> Another thought George. do you have any hardware that could exert an IRQ
> before it has been initialized to do so?
> Cheers, Gene
There are only two boards on the expansion port. The disk controller and the
I/O board. The I/O board generates no IRQs but I disconnected it anyway for
I tried another GIME chip and the results are the same. I'm wondering if it
might be a chip that controls the memory that has failed. I don't know where
the schematic is for the CC3. I've got the book stashed away somewhere.
Does anyone remember why we modified the circuit at IC-9 to add a 74LS02?
I'll try another '02 there, since it's socketed.
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