[Coco] Broken CC3

[George Ramsower]

 Well, I'm stumped.

 I found the power supply was clean after all, I think.

 The computer seems to work fine as long as I don't access the disk drive.

 To bring you up to date I've changed:

 The CPU, Gime, RAM Board, disk controller and disk drive and C14. That's 
the one just after the .1 ohm resistor from the voltage regulator 
transistor. The .1 ohm resistor is not in the circuit as, I'm using an 
external power supply.

 AC noise on the 5V line is < 20mv. However, I'm seeing that noise on the 
ground also. So I suppose this is just noise on the power line to the scope.

 Right now, from power up, when I DIR drive 0, it steps over to( I think) 
the directory track and then crashes. After a crash, I reset twice because 
the first reset doen't reset to RSBASIC. The crash gets better and more 
colorful. Upon the second reset, I get the initial startup screen. This 
time, when I do a dir, the disk doesn't find the track, tries again and then 
crashes when it( I think) gets to the dir track.
 My 3.5 drives, upon power up, moves the head to track 0(I think). So after 
the crash, the drive isn't where the coco is expecting the head to be. 
Therefore, it goes to the wrong track, doesn't find the directory and tries 
again after moving it back to zero, tries again and crashes. I'm used to 
hearing this and I'm pretty sure it is stepping the correct number of tracks 
before it crashes.

 I hope my info is not to vague or stupid sounding.

 Suggestions are welcome!

 Is it possible the ROM in the coco could have failed? Has anyone ever had a 
ROM failure in a CC3?

George