Mike's PCjr Page

As I've already told in my introductory message, I'm still working on getting a fully operational PCjr. After repairing a motherboard and meanwhile I'm looking for a missing power card replacement, the only problem that remained was how to feed the PCjr with disks and check if the drive and controller were working 100%.

The first problem that I've found is the PCjr 360K disk drive, seems to be extremely nitpicking. I haven't been able to write a PCDOS 2.1 working boot disk using any of these methods:

1) Formating & writing with a 1.2MB HD drive. Obviously this didn't work at all. No signs of boot...
2) Formating with a Tandy 1000EX and writing the files with the HD drive. The Tandy booted; but the PCjr didn't show signs of boot "life".
3) Formating & writing with the 1000EX. The PCDOS booted fine in the Tandy; but no booting at all when inserted in the PCjr.

Tested several floppies and even replaced the drive with another 5.25 drive (not sure about the drive, it can be badly configured).

Finally I gave up and focused my tests towards the 3.5 drives. Using a unmodded standard PC cable (after checking pinouts) looked pretty easy to setup, the power connector was easy to adapt using a 3.5 molex plug converter. About the drives, out-of-the-box PC drives are configured as B: drives (PCjr likes this ) and they don't need to drive the DC/RDY signal to pin 34 (PCjr doesn't use the signal at all). The DD/HD setting must not be a problem as I'm always using DSDD media.

After transferring the 5.25 PCDOS boot disk to a 3.5 floppy I started to test several 3.5 drive units and finally.....success!. It suddenly worked and boot without flaws to a DOS 2.1 prompt!.

The following drives are tested to work and booted fine without mods, just plug and play:

• - Panasonic JU-257A526P

• - Mitsumi D359T5

• - Alps DF354H911A

The only drive that failed miserably and I'm sure that it's not broken, is the Samsung SFD-321B both rev.5 and rev.9, they always gave a "disk boot failure".

I'm still testing the new 3.5 drive reading and writing files; but if it finally works fine, I'll paint it (sadly I doesn't have black bezel units) and I'll mount it in the PCjr using a bay adapter. Photos will come soon!

Things are getting better!

I've had mixed success with 3.5" HD drives replacing 5.25" DD drives. You'll find on the drives that can not boot that they will read and write fine if the machine is booted from a 5.25" drive, but you can not boot from them directly. I suspect that there is something different about the drives and they are reading that first boot sector wrong, and until something resets them or gets the speed setting correct they will not work.

Floppy drives are pretty stupid devices though - there is no firmware on them. They should be detecting double density media using the switch or optical sensor and the lack of a hole on that side of the diskette. And they should be getting the clock rate from the floppy controller card. So I can't figure out how they can not be reading the first sector correctly.

Sounds like a job for an oscilloscope. I have one, but it's not really up to the task - I need an upgrade.

Has anybody else tried this recently? It works perfectly with a 3.5" DD drive, but the HD drives sometimes have this problem.

As for the 5.25" drive - don't give up on it. Clean and lube the rails. Clean the head carefully - don't knock it out of alignment or leave Q-tip (cotton) fibers on it. (Use a cleaning disk if you can.) Floppy drives are pretty simple and I've had very few just go bad. If it is a belt driven model that is a potential problem; CopyIIJr with the /T option can tell you the rotational speed to make sure the drive is operating in spec. Direct drive (no belt) models are generally superior.

I think that even a 5.25" HD drive should work fine. The problem with those is the track spacing; you won't be able to read it in a different machine without a software utility.

It works perfectly with a 3.5" DD drive, but the HD drives sometimes have this problem

That's the good part. All of my 3.5 drives are (initially, withoud modding) HD ones and worked fine with the PCjr and both disk controllers. Seems that they're consistently compatible, at least the models I've listed. As an example, I've two identical Mitsumi drives and both worked; so seems that it doesn't relies on random.

As for the 5.25" drive - don't give up on it. Clean and lube the rails. Clean the head carefully - don't knock it out of alignment or leave Q-tip (cotton) fibers on it. (Use a cleaning disk if you can.) Floppy drives are pretty simple and I've had very few just go bad. If it is a belt driven model that is a potential problem; CopyIIJr with the /T option can tell you the rotational speed to make sure the drive is operating in spec. Direct drive (no belt) models are generally superior.

Already blowed the dust, cleaned the heads with q-tips and lubed the rails; but without changes. The best looking drive sounds fine and the dusty one, still sounds noisy. The scratchy sound comes from the radial axis, not from the rail movement and I have no idea of how can I reach this axis. Anyway, both moved the head back and forth one time and then stay quiet. No read at all or "disk boot failure" messages.
They're belt models; but the belt looked in good shape, I'll try to measure RPM; but I cannot load CopyIIJr without a 3.5 drive plugged in right now. Maybe I need a modded disk controller card able to support two drives . As a last resort if I keep trying, I can install one of the PCjr drives in a PC and write a boot disk this way, it must work, isn't it?. Of course, I'm not sure at all of this procedure, I'm afraid that these drives aren't PC compatible, the empty pin#34 looks like an epic fail to me.

Mmmm, too much struggling with floppy drives, I need a jr-IDE right now!

I've written boot disks for my PCjr by moving the drive to a PC, before. Gives me much more reliable results than using the 360k Teac drive I normally keep in the machine (although that one will work about 75% of the time).