[Coco] Fwd: Re: Broken CC3
flexser at fiu.edu
flexser at fiu.edu
Tue Sep 16 01:05:05 EDT 2008
I assume you've thoroughly cleaned the upper and lower surfaces of the edge connectors?
You might also try reseating the Disk ROM.
Other possible culprits: a bad disk cable, or a bad logic chip in the disk controller, or the disk controller chip itself. (All of this is a lot easier to diagnose if you have the luxury of having access to a second disk controller and cable!) Some of the 74xx series logic chips there may be more than one of, so if they are socketed, you might try interchanging them and seeing if the symptoms change.
Are you doing this with a known good already-formatted disk?
If not (I've lost track of what transpired earlier in this thread), I'm guessing that formatting failed, so naturally
any reads from the disk will also fail.
If you have some documentation on DSKCON (see the appendix of the Disk Basic manual), you might try some low-level sector IO by poking parameters into $EA-EF and looking at the error code that is found in $F0 after you EXEC the address of DSKCON (which is contained
in $C004-5 or something like that--something in the $D6xx area.)
>On 9/15/08, George Ramsower <georgeramsower at gmail.com> wrote:
>> 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?
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