[Coco] Broken CC3
georgeramsower at gmail.com
Fri Sep 12 11:08:33 EDT 2008
> ----- Original Message -----
> From: "George Ramsower"
>> 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.
> 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
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.
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