[Coco] Broken CC3

[George Ramsower]

----- Original Message ----- 
From: "Darren A"
> This sounds a lot like a blown HALT in the CPU. From what you say, the
> crash doesn't occur until the head is over the correct track, and the
> sector is ready to be read. That's when the HALT line is activated.
> What's strange is that you say you've replaced the CPU. It seems
> unlikely that both CPU's would have a blown HALT line, but who knows.
>
> You can test it by starting up the CoCo in Disk Basic using a standard
> CoCo disk controller. Then enter the folllowing program:
>
> 10 POKE &HFF48,3
> 20 POKE &HFF40,128
>
> When you run this program, the CoCo should freeze for about 7 1/2
> seconds before the OK prompt appears.  If it crashes, or if the OK
> prompt never appears, or if the OK prompt appears immediately then the
> HALT line is the likely culprit.
>
> Darren

Well, it came back exactly as you suggested. About eight seconds.

First, I got excited and re-crimped the controller's edge connector on the 
Y-cable and tried it
Same stuff.
So I typed in that simple two liner.... sounds familiar.... Ranbow's "One 
Liner" then "Two liner"

Heck!

 I'm reluctant to do so but, I may have to take the steps to put another 
board into that cabinet to see if the problem is the coco or something else. 
This is going to be a major project(for me), I'm lazy.
I think I have another CC3 somewhere that I could put into it. I'll look 
around.

Meanwhile,

More suggestions are welcome.

> On 9/15/08, 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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>
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