First post, by Durandal
- Rank
- Newbie
Hey all,
I've been trying to replace the dead FDD in this Japanese IBM PS/55 (essentially IBM Japan's PS/2, it's a 386 MCA machine) and am having trouble getting it to read 1.44MB disks.
https://retrocomputing.stackexchange.com/ques … -in-an-ibm-ps-2
http://www.vcfed.org/forum/showthread.php?508 … -2-floppy-drive
What I've done so far is follow the pinout on that site + thread above: wired the 34-pin cable, power cable, and added 5 x 4k7 resistors bridging pins 8, 26, 28, 30, and 34 to 5V on the floppy drive itself (it wasn't working without the resistors). It didn't work at all with pins 12 and 16 wired to for 'drive select A' and 'motor enable A', but a friend suggested that I re-wire both for drive B and then the FDD started to read 720KB disks perfectly. However, it outright refuses to do anything with a 1.44MB disk. When I try booting from a known good 1.44MB floppy, the drive will seek 2 times and then boot from the hard drive, and also does the same thing when I've booted DOS from the hard drive and am trying to access a 1.44MB disk.
Luckily I had the foresight to copy the PS/55's reference diskette to the hard drive. Booting into the setup from the HDD, my only options for Drive 0 (A:, I'm assuming) are either 3.5" 1.44MB or 2.88MB, and Drive 1 (B:) has those two options plus 5.25" 360KB. I tried setting the only active drive to Drive 1, 1.44MB 3.5", but that stopped the FDD from working with 720KB disks. Setting either Drive 0 or 1 to 2.88MB 3.5" also stopped the drive from working as it was before.
I had this exact same problem when replacing the floppy drive in another Japanese PS/55 (that one had the PS/1 style 34-pin connector with integrated power) and all I had to do to fix the problem was ground pin 2, which is 'density select' on a standard floppy drive. I thought the same might be the case for this 40-pin edge connector style PS/55, but grounding pin 2 did nothing. Also, it might not be relevant but I thought it strange nonetheless: that PS/1 style PS/55 auto-detects the new standard FDD as 2.88MB 3.5", but works perfectly with 1.44MB and 720KB disks; I have no 2.88MB disks to test with but I'm sure they won't work since the drive isn't capable of it.
After some more research on this it appears that some PS/2's don't have 'media sensing' but modern drives do (I think?):
http://ibm.kanotech.org/ps2/
That page says that a drive "that supports CMOS" is necessary but I can't find this information anywhere else, and I don't really know what to do about it. Do I need a special type of 34-pin drive? Or am I doing something wrong?
Any and all help is greatly appreciated! I'm planning to try my hand at creating a plug-and-play solution to this if I manage to figure it out.
Thanks and best regards,
Jordan
