Apple //c Problem Reading Disks?

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Apple //c Problem Reading Disks?

Hi,

I have an Apple IIc - ROM 255 with the serial port mod (oscillator fitted).

I also have an external Drive //c. My problem is that the machine will not read from the floppy drive. I've tried swapping the drives around but no difference. I even tried plugging an Apple Disk ][ drive into the external Drive //c cable, as well as directly to the //c motherboard - same issue.

Funny thing is that it does seem to work very briefly when the machine has been left for a while and is first fired up.

I'm wondering whether this is a know problem? Could it be an issue with power supply - maybe filter caps? Or the caps in the drives perhaps?

I need to do some more testing to try further identify where the problem is - tricky one!

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Oh - another thing - the driv

Oh - another thing - the drive continues to run on after the Check Disk Drive message.

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Maintenence?

There are two standard maintenence issues with these drives:

1)Dirty magnetic read/write heads.
2)Disk motor speed not calibrated.

Try cleaning the heads, then calibrating the disk speed. There is software for disk drive speed calibration, and you need a micro flathead screwdriver to adjust the motor control potentiometer attached to the drive. There should be a small hole under the built in drive to access the pot.

If none of the above works, are you sure that you are using a viable floppy disk? Sad to write, but some go inoperable after awhile.

Mutant_Pie

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Thanks Mutant_Pie, I did s

Thanks Mutant_Pie,

I did set the drive speed (under fluro light using the strobe wheel on the bottom of the motor pulley).

I did clean the head early on - I'll try cleaning the head again - maybe these old disks are shedding particles.

I'm hoping its not the Integrated Woz Machine (IWM) chip gone belly up.

Failing that I might go down the road of replacing the logic chips on the analog board in the drive.

Strange that the drive does not stop spinning after the Check Disk Drive prompt - light stays on and drive continues to spin.

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Re: Thanks Mutant_Pie,

Strange that the drive does not stop spinning after the Check Disk Drive prompt - light stays on and drive continues to spin.

Does it do that, even without inserting a disk? If so, I'm leaning towards hardware failure.

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Yep

Yeah - stays on regardless of whether you put a disk in or not. I cleaned the head - same problem. Wonder if it could be power supply related? I'm going to peek inside the internal power supply and check it visually for problems (capacitors).

I've got another //c here so I'm going to try the disk drive in the other one to pinpoint where the problem is (drive or motherboard).

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Some Diagnostics

I found that with a clean disk it does boot ok - the problem is that the drive stays selected (spinning) when it should be off.

So,I've done some initial hardware diagnostics - pin DR1 on the IWM (Drive Select 1) is staying low - not going high like it should to turn the drive off (pin is active low so de-selected when high).

It does however go high on reset - a reset will stop it spinning - so I dont think there is a short pulling it low - strange.

I need to read the firmware listing to understand how the drive is turned off when the check disk prompt is displayed.

Does anyone have a nice clean scan of the //c Tech Ref Manual? Specifically nice clean schematics?

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More diags

Ok looking at the firmware reveals that a write to address C0E8 (49384) should stop the drive, and a write to C0E9 (49385) should start it spinning.

If I reset the machine then do a POKE 49385,0 to start the drive motor, it starts.

However a POKE 49384,0 will not stop it. Im guess this memory address (C0E8) is mapped to the IWM???

If so, seems I have a dud chip so I need a replacement IWM chip.

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