PCjr Drive Calibration?

[jason]

Does anyone have instructions on how to clean up and calibrate the primary 5 1/4" DSDD drive on the PCjr? My main drive works great, but a spare I have can't read any disks and I'm not sure how to get it working again. I did a head cleaning on it, but that's about it. The motor spins and the head moves, so that's about all I know at the moment.

Also, does anyone have instructions on how to modify the junior to allow for 2 floppy drives? I remember seeing on this board that it had been done, but did not see any instructions for how it was done back in the day.

[Brutman]

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.

Also look at https://www.brutman.com/PCjr/pcjr_docs.html ... the original 2 drive modification is documented there.

[jason]

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.

Alright, I've cleaned the heads (using an old 5 1/4" cleaning kit I have plus some isopropyl alcohol) and the rails, but I still am getting a "General failure" trying to read good disks. Should I try cleaning the heads a few times more or should once be good enough? I seem to recall that you should run the cleaning disk for about 30 seconds to clean the heads?

The head moves around just fine but it just doesn't seem to be able to read data.

Any other suggestions would be welcomed .

Oh, and thanks for the link to the dual drive article! I missed that one somehow.

[Gremlin5]

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

[jason]

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

It is not reading any other disks....I had not tried to format a disk with the drive and then read it back. I'll add that to my todo pile.

Thanks for the manual, I did not have one for the main drive. I'm a software guy though so I may have questions after I have time to read through the manual .

[jason]

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.

Alright, I had some time today to tinker with my non-working 5 1/4" drive. To answer your question, no, it can't read anything, nor even format a disk. I tried to format a disk and got the following error. This is with a perfectly good disk that I tested immediately afterwards in my good drive with no issue at all.

Code: Select all

Invalid media or Track 0 bad - disk unusable

I 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.

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). I was attempting to check the drive RPM because it sounds like it is not running the correct RPM and the service manual says to connect power and no data cable. When I connect pin 16 (motor on) to ground, the drive spins up to a much higher speed, but as soon as I remove the connection it resumes spinning slowly. The other drive I have does not do this so I believe this is a clue.

Looking at the service manual the circuit that connects pin 16 (motor on) to the motor is independent of all other pins. I checked for continuity between pin 16 and ground with no cable attached and it shows as open circuit. I may show the circuit diagram to some of my electrical engineer friends and see if they have any suggestions.

The only idea I have is could the motor speed adjustment be so far off that it turns the drive slowly even when the motor drive signal isn't grounded?

I may also try some of the tests I found in this YouTube video using "ImageDisk" to see what I learn from it:
https://www.youtube.com/watch?v=VZ9xhFk ... CRetroTech

[DoctorOctal]

I 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 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).

This probably isn’t a big issue by itself. If the drive doesn’t spin on its own when the ribbon cable is connected and the PCjr is on, it should be fine. Otherwise you might want to replace Q13, which is a common-as-dirt PN2222A transistor that acts as the switch for the drive motor circuit. In any case, I doubt it’s a problem for the motor speed if the motor does speed up when you ground pin 16.

That said, the rotation speed may indeed be the reason the drive doesn’t work.

Before checking and perhaps adjusting the speed, make sure everything turns freely as it should. The lubrication on the Qume drives can get gummed up.

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.

Checking the rotation speed:

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.

Adjusting the rotation 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.

Checking the rotation speed under load:

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.

Tightening the belt:

The QumeTrak 142 drives use a fabric belt, so it isn’t going to break apart the way rubber belts do in time. However, the belt will loosen a bit and lose its grip, causing it to slip against the pulleys. In that case, the pulleys will spin more slowly and erratically (if at all) under load. Sometimes there’s no way to compensate, and the belt just needs to be replaced. I often find, however, that I can add enough tension to make it work well again.

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.

[jason]

I 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"?

Not being 100% sure what that meant I did some testing for the Index sensor (Qume 142 Maintenance manual page 142) and compared it with my good drive and that all seems to work correctly. So I'm guessing that's not what it's referring to.

I haven't had time to look into the RPM yet to verify it is correct.

Oh and I spent quite a bit of time wandering the oldskool FTP site, there are some nice finds in there!

[jason]

Okay, I had time to try and adjust the RPM on the drive and could not get it to the correct RPM. I even took my good drive out under the same fluorescent tubes and saw that it was showing a good solid 300 RPM. But for the life of me I could not get this drive to the right speed.

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? I tried booting from a completely clean DOS 3.3 boot disk and that did not help either.

ImageDisk utility: http://dunfield.classiccmp.org/img/index.htm

Video showing usage of the tool (around 8:50 into video): https://www.youtube.com/watch?v=VZ9xhFk ... CRetroTech

Command line argument used

Code: Select all

testfdc a: 360

Fails all tests and does not even attempt to access the drive (as in no motor on, no nothing). The same is true for the IMD.com tool and the RPM test therein.

Source code for testfdc is even provided in C; however, since I am not used to accessing hardware I'm not sure what I would be looking for as to why it's not working. http://dunfield.classiccmp.org/img47321/imd118sc.zip

[DoctorOctal]

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”?

This is what I mean by the codes’ not being terribly illuminating. Basically you can interpret this as “couldn’t read the disk”. It doesn’t really pinpoint the problem, though it probably rules out various controller issues. In fact, it leaves open the question of whether the test correctly wrote something on the disk for it to read back. But given your inability to read other disks, I think we can safely assume a reading problem.

Address marks delimit the metadata area for each sector on the disk. See: https://nerdlypleasures.blogspot.com/2015/11/ibm-pc-floppy-disks-deeper-look-at-disk.html

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?

I haven’t personally tried ImageDisk on a PCjr but am not surprised that it didn’t work. It accesses floppy controller hardware directly—not through the BIOS or DOS—and makes assumptions that don’t apply to the PCjr, including the IO port to use. The PCjr is mostly PC-compatible from the BIOS up, but at the hardware level it’s a rather different animal. You need something that specifically supports the PCjr.

Copy II PC 6.0 can test drive speed on a PCjr:

Code: Select all

copyiijr a: /t

You shouldn’t really need a program, however, when you have the drive out of the chassis and can see the bars on the pulley. If the bearings are reasonably lubricated and you don’t have a diskette in the drive, the drive should be able to reach 300 RPM and well beyond even with a slightly loose belt.

When viewed from the bottom, the drive shaft turns counterclockwise. If the speed is too low, the bars on the pulley will appear to move clockwise. If it’s too fast, the bars will move counterclockwise. If the speed is way off, the bars may not be of much help, but you can get a sense of which way it’s wrong more intuitively: A quiet, leisurely spin? It’s too slow. Spinning in high gear with noticeable motor noise? Too fast.

Usually speed problems are due to gummed-up bearings and old belts. Once you get the bearings lubed, the factory speed setting should be fairly close to right. Then it’s a matter of getting enough tension on the belt to avoid a sharp drop in speed when you put a diskette in the drive.