Using PCJr Diskette Drive in other machines

Hardware questions and modifications

Using PCJr Diskette Drive in other machines

Postby knightcrusader » Tue Dec 29, 2020 12:03 am

This may be a stupid question, so please forgive me ahead of time.

When I was at Computer Reset last month, I picked up some NIB PCJr Diskette drives for a friend with the idea of using them in a regular PC. You can do that, right? For some reason I remember reading or hearing from someone that they are not quite right and need some modifications to work on a regular floppy controller - something about needing terminators? Does anyone here have any information that can help me with this?
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Re: Using PCJr Diskette Drive in other machines

Postby DoctorOctal » Tue Dec 29, 2020 4:35 am

Yes, you can use the PCjr drives in other machines. In fact, the IBM Portable PC (5155) came with the very same drives (QumeTrak 142). They’re just 360 KB, double-sided, double-density, half-height PC drives.

The drives you get with the PCjrs don’t come with termination resistors. They’re not needed for the PCjr, and you only need them for other PCs if the drive is the last one on the drive cable (typically making it drive A).

There’s a DIP socket on the drive’s PCB where you can plug in a 150-ohm isolated resistor array in a 14-pin DIP package. If you can’t pull one from another drive, you can simply buy one. The Bourns 4114R-1-151LF should work: Mouser, Digi-Key

When putting the drives in later PCs, you might use resistor values of 330 or 1000 ohms instead. The best value depends on the controller and cable length, not the drive itself.

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Re: Using PCJr Diskette Drive in other machines

Postby DoctorOctal » Tue Dec 29, 2020 5:23 am

The 150 ohm termination value seems to have come to 5.25" drives from the earlier days of 8" floppies and long drive cables. A value of 1000 ohms (Mouser, Digi-Key) might work as well or better in practice in PCs, old or new. In any case, I don’t think the exact value is critical as long as the drives work reliably.
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Re: Using PCJr Diskette Drive in other machines

Postby knightcrusader » Tue Dec 29, 2020 3:29 pm

Awesome, thanks for the info. That helps us out. I guess I'll throw some of those into my next mouser order since I am working on one.
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Re: Using PCJr Diskette Drive in other machines

Postby Gremlin5 » Sat Jan 02, 2021 7:57 pm

The face plates on Qume142 are a bit smaller than normal drives.

Qume142 are 41.5 mm tall and 145.5mm long
Normal drives like Alps, Y-E Data or TEAC are 43.0 mm tall and 148.5mm long

Not a big deal but you end up with a bit more of a gap around the face plates to drive bay openings when putting in standard bays.

I have picked up 4 of these drives ranging from $12 to $17 for replacements in any of my PCJrs. One of my regular PCJrs came with a TEAC drive in it and it seemed to fit just fine but one of my PCJrs with the Racore Drive Two housing someone had replaced that drive with another brand and the drive locking handle didnt clear the opening so they filed a crescent shaped relief in the housing so it would clear.... still trying to figure out how to fix that as it bugs me since I have spare Qume drives to put in it. Probably rebuild the edge with solvent welded abs as I have on other cases.
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Re: Using PCJr Diskette Drive in other machines

Postby ckreling » Fri Jan 29, 2021 5:39 pm

I put one in an older HP Kayak Workstation.

You just need a PC old enough that has the 5.25 360K BIOS setting for the floppy.

I use the Kayak that I got on eBay for $35 as my 'tweener machine to write PCJr disks.
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