Hi there, Ive got a Commodore PC40-iii that Im having a strange problem with. No matter what floppy drive I put in (360k, 720k or 1.44mb) it will not boot from it, but if I put same drive in my Pentium 75 machine, it works like a charm. Ive tried the straight thru floppy cable that came with it, but that cable could not detect the drive at all. Ive tried a modern one that has a twist in it and it sees and tests the drive, but will not boot at all. The only difference Ive noticed is that the drive seems lazy in the commodore compared to the pentium machine. If anyone has a suggestion, it would be good.
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Commodore PCiii-40 floppy drive no boot
- Thread starter Dunwood84
- Start date
Ruud
Veteran Member
First: the PC40-III uses the straight thru cable. And second: the drives use a different jumper setting. If it works in a standard PC, it won't in a Commodore PC unless you change some settings. And that is not possible with all drives.
Please contact me in private, see my site for the email address, then I can have a look at the original drives so I can tell you how the jumpers should be placed.
Please contact me in private, see my site for the email address, then I can have a look at the original drives so I can tell you how the jumpers should be placed.
Suspect this might help:
Adding the 3.5 as a second drive worked fine as long as the cable remained straight and the Commodore 5.25 is primary drive. Trying to use a flip style cable results in drive not ready/floppy configuration errors and the like.
Back when this thing came out, most drives had 4 jumper positions to set DS0 through 3 and used straight through cabling. Using modern drives is a bit of a problem here in that they're set to DS1 and expect you to use a flipped cable to determine A: or B: The PC40-III I encountered, expects A: to be on DS2, and B: to be DS1 so flipping 0 and 1 as most systems expect, won't work here. Further, there is only one motor line on pin 16.... which should not 'flip' or move.
I ended up modifying a flippy cable to allow both drives to be set to DS1. Instead of flipping 7 wires/pins 10 through 16, only flip 3 wires 10 11 12. Then change the 5.25" to DS1 instead of DS2 and you can have either in A: or B: working properly.
I believe sometime after serial number 4500ish, Commodore revised the board to use the IBM AT/flipped cable, as the service manual suggests a revision 5 board has this scheme implemented on the floppy interface.
Only time I ever needed a logic probe to install a floppy drive!
All the best.
Stuart
Adding the 3.5 as a second drive worked fine as long as the cable remained straight and the Commodore 5.25 is primary drive. Trying to use a flip style cable results in drive not ready/floppy configuration errors and the like.
Back when this thing came out, most drives had 4 jumper positions to set DS0 through 3 and used straight through cabling. Using modern drives is a bit of a problem here in that they're set to DS1 and expect you to use a flipped cable to determine A: or B: The PC40-III I encountered, expects A: to be on DS2, and B: to be DS1 so flipping 0 and 1 as most systems expect, won't work here. Further, there is only one motor line on pin 16.... which should not 'flip' or move.
I ended up modifying a flippy cable to allow both drives to be set to DS1. Instead of flipping 7 wires/pins 10 through 16, only flip 3 wires 10 11 12. Then change the 5.25" to DS1 instead of DS2 and you can have either in A: or B: working properly.
I believe sometime after serial number 4500ish, Commodore revised the board to use the IBM AT/flipped cable, as the service manual suggests a revision 5 board has this scheme implemented on the floppy interface.
Only time I ever needed a logic probe to install a floppy drive!
All the best.
Stuart
Error above. I don't appear to be able to delete edit my original message... but should say flip pins 12 13 and 14 up there for a cable that lets you use drives set to DS1 for one of these older PC-40 III's. If in doubt, check the pin-out yourself... you want to swap DS2 with DS1 on the primary drive end of your custom flip cable. Easy to screw up. Good luck. 