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Again a faulty PS/2 floppy drive

pcdata76

pcdata76

Experienced Member
Joined
Apr 9, 2015
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Location
Germany, Munich
Hi,

Last week i've picked up an IBM PS/2 model 60 (8560-041) from junkyard. During the boot it throws 161, 163, and 601 errors. CMOS battery was totally empty, i replaced it with a CR-P2 6V lithium battery. Removed floppy drive and cleaned heads and 40-pin edge connector. Relubed step motor power screw. This time it didnt throw 601 but still couldnt boot from reference disk.

I made an adapter cable to connect standard floppy drives but none of the drives that i've own (two different mitsumi and one tech-media brand) worked. Actually whenever i power the pc up, it is doing usual floppy seek, does not give an error and tries to boot from floppy but after 2 attempts using F1 key, it drops to basic.

After reading relevant topics on internet, i tried to repair its original drive. I made a reverse adapter to connect it to a standard PC using 34-pin interface and regognized successfully from computer. I checked the drive using imagedisk 1.18 DOS (it has a very good alignment interface, you can seek track to track, select head to read/write etc.) and saw that step motor is not functioning well. It misses steps or can't seek one full track. For example i start to seek from track0 one by one but after some point it can't seek one full track and stops reading data due to the positioning of the head somewhere between tracks. Either step motor or step motor driver IC seems to be faulty. Drive brand is ALPS and IBM P/N is 90X6766.
ps-head movement is flawless after removal of step motor, guides/rails are not sticky.

Anyway, i have to find a way to boot this computer from reference disk. Anybody has an opinion for any compatible IBM or non-IBM brand floppy drive with this PS/2 model 60? For now, i dont care about the physical fit of the drive. I couldn't find an exact replacement on ebay but there are 2.88 later model PS/2 drives, are they compatible with model-60 (at 1.44 mode of course)?

ps2- After floppy seek, i checked the density signal on pin 2 of the drive. Normally it should be 0V (low) for HD and 5v (high) for DD mode but in my case, signal is always high (both with standard drives and original faulty drive). In a similar topic, i've read that standard drives could be detected as 360kB. By considering this, i made a try using a 360 kB 5.25 drive and DOS boot disk stamped with reference disk signature using refstamp utility but it didn't boot as well.
 
Perhaps someone else can comment further, or you may be able to find something by searching these forums or elsewhere, but I recall hearing that those drives had capacitors that fail and cause drive problems.

Long story, but I owned and tinkered with a number of PS/2's from that era...30/286, 50, and 60...the floppy drives were the biggest problem at that time (1996-98 or so). I've got two or three decent 50/60's here, and last I checked, only one good floppy drive.

Wesley
 
Same here. The floppy drive in my model 70 and 80 sounded healthy but couldn't read or write disks until a few SMD caps were replaced.
 
I know mitsubishi branded drives are prone to capacitor failure and mostly came back into health after replacement, but is there any ALPS which can be turned into life after recapping?

Update: I found a solution to use generic drives in PS/2 which is explained here http://webpages.charter.net/zip4dos/PS2/ and it definitely works!
Short story about the difference between modern fdd's and PS/2 drives. Other than slight connector pinout, signals on pins 8,26,28,30,34 does not have pull up resistors on modern drives because pull-up of these pins are done by the modern floppy drive controllers which PS/2 controller does not provide. These signals are pulled up on original PS/2 floppy drive. If we pull these pins up by soldering a suitable value resistor (between 1k~10k, i used 4k7 and 10k 1/8W resistors found in my junk box) we can use them in our PS/2s.

Here is my work on a Mitsumi drive:



There is a 40-pin connector on the motherboard. Pinout of pins between 1-34 are exactly the same as generic 34-pin floppy controller pinout. Pin 38 is +5V and pin40 is +12V (which is not needed by modern floppy drives anymore) Ground can be taken from Pin39,37 etc. since all ODD numbered pins are ground. According to this info, i built a special cable.

Parts needed for the job are:
1- One or two 34-pin female IDC connector
2- One 40-pin female IDC connector
3- One or two 4-pin floppy power connector (i used one from a scrap power supply)
4- 40-pin ribbon cable around 20~30 cm in length.
5- IDC crimping tool (or some other method, i used vice grip)

Operations:
1- Crimp 40-pin IDC connector to the one end of the ribbon cable. Align arrow mark on the connector with cable#1(red).
2- Separate cables around 7-8cm from between cables 9-10, 16-17 and 34-35.
3- Crimp 34-pin IDC connector to the other end of the cable as in the original floppy cables by twisting the part between 10 to 16. Align arrow mark on the connector with cable#1(red).
4- If you want to add a second drive, crimp another 34-pin IDC connector to the untwisted (straight) part of the cable. Align arrow mark on the connector with cable#1(red).
5- Separate cables #40, #39 and #38.
6- Connect yellow (+12v) cable of 4-pin floppy connector to the cable#40 and insulate it with tape.
7- Connect black(ground) cables of 4-pin floppy connector to the cable#39 and insulate it with tape. (You may prefer to connect one black to #39 and one black to #37, doesn't matter, it depends on you)
8- Connect red(+5v) cable of 4-pin floppy connector to the cable#38 and insulate it with tape.

Be careful to plug 40-pin connector with correct orientation to the board since some 40-pin connectors are not keyed to prevent reverse plugging.In case of reverse plugging, 12V will be supplied to the logic board and will fry the drive (and worse, controller too) Reverse plugging of 34-pin cable does not make harm, if floppy drive light blinks at the same time with power on, you can suspect from it. It is even better to check the voltage on pins of the floppy power connector before plugging the floppy drive while computer is operating.

After this slight modification, my PS/2 model 60 is booted from reference disk successfully ;) Now, i have to make an adapter to fit the generic drive in PS/2 drive bay properly. I can request the help of my friend having a 3D printer :D
 
Excellent info, thanks for sharing!

I wonder how it work would to make a small PCB to either plug into the motherboard or go inline in the cable to do the same job...?

Wesley
 
wesleyfurr said:
I wonder how it work would to make a small PCB to either plug into the motherboard or go inline in the cable to do the same job...?
Click to expand...

Piece of cake, all the modification does is add a few pull-up's, swap a signal or two and split off the +12V power etc.
 
wesleyfurr said:
Excellent info, thanks for sharing!

I wonder how it work would to make a small PCB to either plug into the motherboard or go inline in the cable to do the same job...?

Wesley
Click to expand...

Such an adapter plugged directly into motherboard connector would be better. You can use it with any floppy drive and standard floppy cable without needing modification on each. And some drives does not have enough clearance on bottom to solder resistors.
 
Any PCB-design experts hanging around that might be interested in throwing something together? :) I really need to figure out how to do that sort of thing myself. Got a personal project I'm working towards, will probably end up trying to design something then. If I can figure something out there, perhaps I can work something up for this, if someone hasn't beat me to it...

Thanks,

Wesley
 
Such a project would be nice ;) I get two more PS/2 computers (one model 30, one 30-286) last week and floppy drives of both are shot as i expected. Even its 30 MB original hdd is intact, but floppies..... A similar project for PS/2 memories could be also good, if possible to adapt.
 
You could make the pcb so that it plugs into the stock cable on the ps2 and transforms it into a standard floppy connectors.

For a prototype you could scavenge a part of the pcb from a non functional drive.

This would allow using both stock and a newer drive in the same machine and also avoid the 12V line problem.

EDIT: Image added

testi.jpg
 
Last edited:
Lost pictures in post#5 are reuploaded to imgur.

8BaGGKn.jpg


tkbLD1k.jpg
 
Hi pcdata76

i hope you can help me,i have been trying to understand the tutorial but it is hard for me to follow since english is not my native language, also because the website http://webpages.charter.net/zip4dos/PS2/ has been deleted and content is not available anymore.

Issue:
i own a PS/2 Model30 8530 8086 , 720k floppy drive, it has a 40 pin connector on motherboard ,40 pin ide cable. I am trying to put a newer (any brand) 1.44 floppy drive on the machine


questions:

1) Your tutorial mentions that pins 8,26,28,30,34 does not have pull up resistors. So we have to solder resistors to those pins, but to where? what is the blue point? 5volt? ground?

8BaGGKn.jpg



2) There is actually an easy way to do the rest of the mod without buying so many cables and connectors
a) you use a regular floppy drive cable (twisted model) + floppy drive power cable + some cable connectors.
ttttt.jpg

b) Pin 40, 39, 38 from motherboard using those 3 cable connectors soldered to floppy power cable.
c) Use normal twisted floppy cable connected directly to motherboard. (note you might need to cut one edge of plastic or sand it with sandpaper so it fits perfectly and does not interfere with rest of pins on motherboard.
ttttt2.jpg




please let me know what you think
and please let me know answer of question #1, where do all resistors end up soldered to , what point is it.
 
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