Mike's PCjr Page

Brutman wrote: ↑Sat Oct 09, 2021 12:05 pm Cleaning the rails and the heads on the 5.25" drive takes care of most problems. There are some instructions on the documentation download page - look at https://www.brutman.com/PCjr/Eugene_Clu ... eaning.pdf. There are probably videos on Youtube.

Cleaning the rails is easy - use a Q-Tip with isopropyl alcohol to remove any gunk that might prevent the head assembly from moving on the rails. Then apply a light coat of sewing machine oil; just a little bit will go a long way.

Cleaning the heads is more delicate and sensitive, as if you screw up you can damage the heads. I'd use a cleaning diskette if you have one. Otherwise, watch a few YouTube videos for the process. I use Q-Tips with 90+ % pure isopropyl alcohol, but some people consider that a crime because the Q-Tip might shed fibers. Compared to the other things you might be removing, it's an acceptable risk. The bigger danger is slipping and damaging the head, or bending things too far when you are trying to get access.

Gremlin5 wrote: ↑Wed Nov 03, 2021 5:10 pm Is it not reading disks at all or is it not reading disks from other drives?

I have had drives go out of alignment where they cant read disks from other drives but can read disks that are formatted on them and read them just back fine.

If you need a PDF maintenance manual on the Qumetrak 142 I found a link to one here http://www.primrosebank.net/computers/m ... floppy.pdf

Gremlin5 wrote: ↑Wed Nov 03, 2021 5:10 pm Is it not reading disks at all or is it not reading disks from other drives?

I have had drives go out of alignment where they cant read disks from other drives but can read disks that are formatted on them and read them just back fine.

Invalid media or Track 0 bad - disk unusable

jason wrote: ↑Thu Nov 11, 2021 5:06 pmI also ran the built in tests for the floppy drive and got an error “C”…which I don’t see listed in the PCjr hardware manual as to what that means…other than it failed.

                DISKETTE DIAGNOSTIC ERROR MESSAGES

MANUFACT. ID = 3EXYZZ

        THE CODES APPEAR IN THE FORM "3EXYZZ", WHERE:

        X=0, SIDE 0
        X=1, SIDE 1

        Y=OPERATION THAT FAILED
        0=RESET
        2=READ
        3=WRITE
        4=VERIFY
        5=FORMAT

        ZZ=ENDING STATUS
        80=TIMEOUT
        40=SEEK FAILURE
        20=NEC CONTROLLER ERROR
        10=CRC ERROR IN DATA FIELD
        09=DMA ACROSS 64K BOUNDARY (SHOULD NEVER HAPPEN)
        08=DMA OVERRUN (SHOULD NEVER OCCUR)
        04=SECTOR NOT FOUND
        02=MISSING ADDRESS MARK
        01=INVALID COMMAND ISSUED TO NEC CONTROLLER

        98=SPEED ERROR
        97=DISKETTE ATTACHMENT CARD NOT PRESENT
        99=READ BUFFER MISCOMPARE WITH WRITE BUFFER

I also tinkered with it on my desk with just a power supply connected to it and noticed that for some odd reason it spins the drive slowly continuously as long as it has power (note: no ribbon cable attached).

1. Gently slip the belt off the pulleys (as described in the manual) and verify that you can spin the large pulley easily with your finger. It doesn’t have to continue spinning much after you let go, but it shouldn’t offer much resistance. If it’s stiff, put some light oil at the intersection of the shaft and the pulley, then turn the pulley back and forth for a few minutes with your finger. The oil will seep in, down the shaft, and into the bearing. You’ll feel the rotation getting easier.
2. Make sure the collet turns freely. That’s the cone on the other side that clamps down on the diskette’s inner ring when you close the drive. It should spin with very little resistance, and the little E-clip visible at the top of the shaft should not spin. If there’s any significant resistance, or if you’re turning the E-clip, you’ll need to lubricate the bearing. Ideally you should take off the E-clip, take apart the collet assembly, and clean and re-lube the ball bearing. However, for a quick shortcut that may suffice, you can just put a few drops of oil between the concentric metal rings at the center of the assembly. Be careful to place the drops precisely and only use a few, otherwise you risk having oil run to the bottom of the collet and subsequently get on your diskettes.
3. Put a couple drops of oil under the motor pulley and spin it counter-clockwise to work them in. Perhaps pull the pulley in and out slightly, too.
4. Once everything is lubricated, carefully clean off any oil near the pulleys (lest it get on the belt) and gently slip the belt back onto the pulleys, small pulley first.

1. Get a light that flickers in time with the mains frequency (60 Hz in the US). Incandescent bulbs and most compact fluorescent bulbs won’t work, but traditional fluorescent tubes and some LED bulbs will.
2. Start the drive motor by grounding pin 16 as you did (or pin 11 of the empty socket nearby).
3. In the flickering light, with the drive turned upside-down, look at the bars in the outer ring on the sticker attached to the large pulley. (The inner ring of bars is for 50 Hz.) If the pulley is spinning at the right speed, the bars will appear to stand still. If they’re drifting only slowly, that’s probably fine. If they’re drifting significantly, you’ll need to adjust the speed.

1. Find the small trimmer potentiometer in the back left corner of the circuit board, just behind the drive motor. It’s usually a blue box with a white circle at the top, which has a blob of red, waxy stuff to hold its current setting. You’ll need to scrape off the red stuff so you can turn the white circle with a small flat-head screwdriver.
2. With the drive upside-down and spinning, adjust the potentiometer until the bars on the pulley are as close to stationary as you can make them. The adjustment is quite sensitive, so it’s hard to be exact. A slow drift is good enough.

1. Once the pulley is spinning properly, put a sacrificial diskette in the drive while it’s still spinning and close the door. The “standing” bars on the pulley should only be affected slightly. If they start drifting significantly or erratically, or if the pulley comes to a halt entirely, the belt needs to be tightened or replaced.
2. If you’ve already calibrated the rotation speed without the diskette and putting in the diskette alters the speed only slightly, go ahead and re-adjust the speed with the diskette in place. After all, what’s important is how fast the diskette spins.

1. With the drive spinning and a diskette closed in the drive, turn the drive upside-down and loosen the two screws holding the drive motor in place. (Use a #1 Phillips bit.)
2. Gently push the motor away from the large pulley until the bars on the large pulley stand more-or-less still. You should have already confirmed the right speed without the diskette in place, so now you’re aiming to get the speed under load to match. The Qume manual advises using their tension-measuring tool, but I don’t have one, and you probably don’t either. Instead, try to put just enough tension on the belt to keep it from slipping and to achieve a speed that’s close to correct. As long as the belt isn’t slipping, you can fine-tune the speed with the potentiometer.
3. While maintaining tension on the motor screws with one hand, tighten them down with the other.

DoctorOctal wrote: ↑Fri Nov 12, 2021 6:15 pm

jason wrote: ↑Thu Nov 11, 2021 5:06 pmI also ran the built in tests for the floppy drive and got an error “C”…which I don’t see listed in the PCjr hardware manual as to what that means…other than it failed.

Try running the tests when the “JJ” service plug is plugged in. That will give you more detailed codes:

Code: Select all

                DISKETTE DIAGNOSTIC ERROR MESSAGES

MANUFACT. ID = 3EXYZZ

        THE CODES APPEAR IN THE FORM "3EXYZZ", WHERE:

        X=0, SIDE 0
        X=1, SIDE 1

        Y=OPERATION THAT FAILED
        0=RESET
        2=READ
        3=WRITE
        4=VERIFY
        5=FORMAT

        ZZ=ENDING STATUS
        80=TIMEOUT
        40=SEEK FAILURE
        20=NEC CONTROLLER ERROR
        10=CRC ERROR IN DATA FIELD
        09=DMA ACROSS 64K BOUNDARY (SHOULD NEVER HAPPEN)
        08=DMA OVERRUN (SHOULD NEVER OCCUR)
        04=SECTOR NOT FOUND
        02=MISSING ADDRESS MARK
        01=INVALID COMMAND ISSUED TO NEC CONTROLLER

        98=SPEED ERROR
        97=DISKETTE ATTACHMENT CARD NOT PRESENT
        99=READ BUFFER MISCOMPARE WITH WRITE BUFFER

These aren’t always illuminating, but at least they’re not just “C”.

I ran the floppy drive test with the JJ test plug installed and got a code “0202” which I believe means “Side 0 - Read - Missing Address Mark”?

Having watched a video online, I figured I would try out this “ImageDisk” utility by Dave Dunfield which does an estimate of the RPM and try to see what is going on. However, I for the life of me could not get the program to access my drives as all. I couldn’t get it to work with either the working nor “bad” drive. Does anyone have any experience using Image Disk on the PCjr?

copyiijr a: /t