[Coco] Broken CC3 => Not broken now!!

[George Ramsower]

 Well, I finally got out another CC3 still in the RS cabinet and connected 
it to the drive in the inoperative coco cabinet. It worked. I was about to 
modify it to run off the power supply in the inop coco cabinet when it 
occured to me to test the Y cable from the inop coco. The Y cable did carry 
the problem to the test unit with it.
 Upon inspecting it, I found a wire broken from the edge connection from pin 
4 (NMI). The solder connection came loose.
 Resoldered it and my CNC coco is back! I never imagined the Y cable would 
have failed. It's not subjected to vibration
 Darrin was correct about the NMI being suspect in this scenario.

 I suppose it was just a bad soldering job on that pin that was just barely 
hanging on and finally let loose.

 Now I can get back to work on my engraving software. Hurray!

George

----- Original Message ----- 
From: "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
>
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