[Coco] Broken CC3

[George Ramsower]

> On Friday 12 September 2008, George Ramsower wrote:

>>----- Original Message -----

>>From: "Gene Heskett"

>>

>>> On Friday 12 September 2008, George Ramsower wrote:

>>>>Darn,

>>>>

>>>> 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 

>>>>and

>>>>all gives the same results.

>>>>

>>>> Suggestions?

>>>

>>> This smells like a memory problem as os9 put it in all ram mode. 

>>> Perhaps

>>> 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 

>> CPU.

>> I think the next thing to try is another GIME chip. I've never had one 

>> fail

>>before.

>> I think I'll try that now and see.

>>

>>George

>>

> 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 
this problem.
 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.

George