[Coco] Broken CC3

[George Ramsower]

> ----- Original Message ----- 
> From: "George Ramsower"
>
>> 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?
>>
>>
>> George
>
> I should have done this earlier...
>
> I looked at the power from the switching supply and there is WAY too much 
> high frequency noise on them.
> Tonight, I will take the supply out and find the bad cap/s. I betcha 
> that's the problem.
> What made me look was the fact that the computer seemed to work okay until 
> I try to access the disk. Then it crashed.
> I did a "dir" in RS basic with nothing in the drive and the computer 
> crashes.
Looking at the 5V line while accessing the disk reveals about 100mv of 
square wave while the drive is stepping. I even bridged a 450uf cap onto the 
5v line earlier and this test was with the cap in place.

Positively the power supply.