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Amiga floppy trouble

C

cosam

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I was tinkering with the old A500 last weekend when it suddenly stopped reading disks. When it tries to boot, it just flicks the heads back and forth three times, then gives up. I dug out an A1200 floppy to try in it last night. It doesn't fit in the case, but seemed to get a bit further: The Workbench screen came up, but then it also had trouble reading the disk. Now booting from the A1200 floppy does exactly the same as the old drive.

I found a schematic and tried swapping the CIA chips - no change. Got a scope on the various floppy signals and they look reasonable, to my untrained eye. Drive select, motor and index pulses are all coming through great. What I'm not sure about, however, is the actual data signal coming from the floppy (pin 30). I'm not sure what to expect, but it just looks like a steady voltage with a very feint analogue signal trying to get through. I thought maybe the chip connected to this pin was pulling it high, but it looks the same even with that pin lifted. I have an external floppy too, but I'm reluctant to try it as it looks like the machine has somehow toasted two drives already.

I wondered about alignment, so tried booting from hard disk and formatting a floppy. No joy there either - it failed whilst verifying the first cylinder. It looks like it can write OK but has trouble reading back.

I'm kinda out of ideas now as to what to try next.
 
cosam said:
I was tinkering with the old A500 last weekend when it suddenly stopped reading disks. When it tries to boot, it just flicks the heads back and forth three times, then gives up. I dug out an A1200 floppy to try in it last night. It doesn't fit in the case, but seemed to get a bit further: The Workbench screen came up, but then it also had trouble reading the disk. Now booting from the A1200 floppy does exactly the same as the old drive.

I found a schematic and tried swapping the CIA chips - no change. Got a scope on the various floppy signals and they look reasonable, to my untrained eye. Drive select, motor and index pulses are all coming through great. What I'm not sure about, however, is the actual data signal coming from the floppy (pin 30). I'm not sure what to expect, but it just looks like a steady voltage with a very feint analogue signal trying to get through. I thought maybe the chip connected to this pin was pulling it high, but it looks the same even with that pin lifted. I have an external floppy too, but I'm reluctant to try it as it looks like the machine has somehow toasted two drives already.

I wondered about alignment, so tried booting from hard disk and formatting a floppy. No joy there either - it failed whilst verifying the first cylinder. It looks like it can write OK but has trouble reading back.

I'm kinda out of ideas now as to what to try next.
Click to expand...

Do you have a spare machine? IIRC, Paula is the chip responsible for actually decoding the data from the drive.
 
Hmm, a little confusing; sometimes 'floppy' seems to refer to the diskette and sometimes to the drive?

Obvious perhaps, but have you completely ruled out bad diskettes?
 
geoffm3 said:
Do you have a spare machine? IIRC, Paula is the chip responsible for actually decoding the data from the drive.
Click to expand...
Yes, Paula gets the data direct from the floppy drive. This is the chip whose pin I lifted, but to no avail. All the other Paulas I have are SMT, so unfortunately it's not something I can swap out. I did dig out another Amiga to test the drive on though, so I'll be trying that shortly. I should be able to compare the data read signal on that machine too.

MikeS said:
Hmm, a little confusing; sometimes 'floppy' seems to refer to the diskette and sometimes to the drive?

Obvious perhaps, but have you completely ruled out bad diskettes?
Click to expand...
Oh, it's definitely the drive - I won't boot from any disk. I tried the same disks in the other machine and they booted fine.

channelmaniac said:
Or dirty heads?
Click to expand...
If only... This is the first thing I checked. They were pretty clean to start with, but now they're spotless.
 
Cosam can try to connect the 500 floppy drive to another compatible Amiga. If disks are read fine then, we can conclude the problem is somewhere on the motherboard. As he wrote at first he almost managed to boot to Workbench using an A1200 floppy drive which then gave up, it really sounds like the fault is elsewhere than the floppy disk, floppy drive or floppy drive cable.
 
How did you get on with this Steve, any luck?

I've been following the thread but can't offer any advice. I'd like to know the outcome though.

I did have an Amiga 500 external drive that the system failed to recognise on occasions. The problem was a dry solder joint.

Tez
 
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