Mike's PCjr Page

Hi All,

I'm trying to wake up the floppy drive in my thrift store find PCjr. Things are not quite working out. I am hoping the collective wisdom here can help.

When booting with the cover removed, I observed that the head assembly would move, but the spindle would not spin. I could hear the belt slipping inside the drive.

I removed the drive from the junior to inspect it. I clearly was not the first person inside this machine as the tabs for the cover were missing and the tabs that hold the floppy carrier were already pre-broken.

On first inspection I noticed that the spindle was very stiff. I gently removed the belt and gently worked the spindle back and forth until I could get it to move. Even then, the motion is not smooth, but it seems to improve with use. Once I felt it might work, I reassembled everything and booted with a new(ish) unformatted disk. The spindle spun and I got the expected non-system disk error.

I then ran the built in disk diagnostics (as described in the Guide to Operations) and could observe the head stepping from edge to center of the disk twice and failed with error code "B" which in the Guide to Operations has the helpful instruction to have the PCjr serviced.

Yeah, sure.



For kicks, I also tried booting with a DOS disk (although, I have no idea is the DOS disk is any good). I also got the non-system disk error.

Given the experience here: is there any common cause for an error code "B" when running the internal diagnostics on a floppy disk? Could it be spindle speed or something else?

I posted in the introductions thread. A little oil should help. It is probably still not spinning at the proper speed. if you look closely at the top spindle, you will see where, just inside the edge, it is supposed to spin. Oil it there. One the one I worked on, moving it by hand had it spinning at the C-clip that hold it on the arm, not where it should. If you need a known good boot disk, PM me with your address and I will make copies of my IBM DOS 3.3 diskettes for you.

Saw your post in the introductions thread. Thanks for following up twice!

I wondered if it was spindle speed. I found your post from Feb 2019 where you wrote about using sewing machine oil to loosen up the spindle when I was initially trying to debug the drive. I am willing to concede I may not have loosened it up enough.

I will give the oil a shot. I will have to pick something up with an applicator small enough to get me in there.

Is there any general consensus on the best oil for the spindle?

Passed Disk Diagnostics - It's alive!

I removed the Disk Drive circuit board to get better access to the mechanism. I cleaned and lube the head rails. I checked out the upper spindle per KenG's suggestion, although it seemed to be fine, I applied a drop of lubricant. The lower spindle was still sluggish/stiff. I couldn't see any way to get lubricant into the bearing without getting it all over. So I removed the belt and kept spinning the lower spindle by hand and it seemed to keep improving. I did this for a while and it seemed to be much improved. I replaced the belt, but reversed it so the rougher outside was now in contact with the spindle wheel and reassembled the drive and junior

Inserted the new blank floppy disk and ran disk diagnostics and passed!!

I inserted my boot disk and failed!

Crud.

Now, this boot disk is hand labeled "Dos 3.3 for PCjr" and looks newer than all the other disks. I suspect it came from my old 286 and was written to a DSDD disk by a 1.2 MB drive. I don't know if it ever worked. Maybe it did, but now it does not because of the narrower tracks and age. Who knows?

I found an older disk labeled "Dos backup." This label looks like the old boot disk I remember. I inserted it, tried to boot and was greeted by a wonderful screeching sound as the drive spindle was turning, but it appeared the disk was not. I quickly opened the drive.

Crud. Crud.

Reviewing some of my old disks, it appears that many of them have contamination on the surface. (Is this the mold I have been reading about?) This one looked fairly clean. Maybe not.

I decided to take a look at my original DOS 2.1 disk. I slid the thick cream colored DOS manual out of its sturdy sleeve and opened the book to the back page where the original DOS and DOS Supplemental Programs disks lived. When we got the computer we were very careful to make copies of the original disks. This disk may have been copied only 2 or 3 times before. It looked perfect. I inserted it and.....

It booted!

Quickly ran diskcopy and diskcomp and restored the original 2.1 disk into its protective cocoon for another day. The new copy booted.

Looks like my next step is to start cleaning disks.

I'm glad you got it working. Finding useable 5.25" disks is getting more difficult every year. Fortunately, I have a decent supply for now. Whenever a disk fails to work, it is a good practice to re-clean the heads. Particles from the bad disk can ruin good ones.

Thanks for the heads up on head cleaning. As I work through my disks, I will definitely keep that in mind.