Odd disk drive error

Hardware questions and modifications

Odd disk drive error

Postby Trixter » Wed Jul 24, 2013 8:18 pm

A while back I had a stepper motor die on a QUME disk drive, and it looked like too much trouble to rebuild it, so I tossed the entire drive and got another PCjr drive off of ebay. Hooking it up this evening, and something is odd: It can intermittently boot, but it can't seem to write anything successfully. Consumer POST shows error "C" after the "MPNP" disk drive test, where it sometimes starts to seek all tracks and other times just dies after the first 0->40->0 seek. I have the Hardware Maintenance and Service manual and dongles and finally had a chance to use them tonight :-) Using the service plug and advanced POST, I get an error "0503" which the manual seems determined to tell me it is a bad testing disk, when I know it isn't. Drive rails are fine (no stickiness). I put a 60Hz light up to the back of the drive and the spinning disc appears to be at the perfect speed.

I'm going to go out and get some rubbing alcohol to see if cleaning the head does something, but has anyone ever seen this type of failure? Ie. something wrong with writing while reads are semi-ok?
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Re: Odd disk drive error

Postby Trixter » Wed Jul 24, 2013 9:38 pm

I've got it narrowed down to what now seems obvious in hindsight: The write-protect sensor is always reporting ON. Every write aborts with WRITE PROTECT.

I blew a ton of air at the thing and it still isn't working. How does one repair the write-protect... thing? It looks like a light and a sensor (I would have thought it was a mechanical switch). Is the light infrared, or should I be able to see it?
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Re: Odd disk drive error

Postby Eric » Wed Jul 24, 2013 11:37 pm

Trixter wrote:I've got it narrowed down to what now seems obvious in hindsight: The write-protect sensor is always reporting ON. Every write aborts with WRITE PROTECT.

I blew a ton of air at the thing and it still isn't working. How does one repair the write-protect... thing? It looks like a light and a sensor (I would have thought it was a mechanical switch). Is the light infrared, or should I be able to see it?

It is an optical sensor. Try wiping it down with a cotton swab dipped in isopropyl alcohol. (There's three in here, but I'm sure you know it's the one above the write protect tab of the diskettes and has yellow/black wires.)
Also, check the connection of the connector for the optical sensors. It might just be loose or corroded.


Trixter wrote:so I tossed the entire drive and got another PCjr drive off of ebay.

Did you really? Hopefully you just stored it away for parts or at least saved the drivebelt in case your new drive ever needs it. :P
...If you did throw it away, I guess it's not the end of the world. There's just a lot of nice parts in there that could've been salvaged.
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Re: Odd disk drive error

Postby Trixter » Thu Jul 25, 2013 3:25 pm

Eric wrote:It is an optical sensor. Try wiping it down with a cotton swab dipped in isopropyl alcohol. (There's three in here, but I'm sure you know it's the one above the write protect tab of the diskettes and has yellow/black wires.)
Also, check the connection of the connector for the optical sensors. It might just be loose or corroded.


Sadly this did not fix the issue. Drive is yours if you want a spare that needs an optical sensor fixed. I have no use for a drive that can't write, nor do I want a drive that has the sensor jumpered to always OFF because that will just bite me in the ass at some point.

Hopefully you just stored it away for parts or at least saved the drivebelt in case your new drive ever needs it. :P
...If you did throw it away, I guess it's not the end of the world. There's just a lot of nice parts in there that could've been salvaged.


I did not save the belt because I incorrectly perceived it to have been part of the problem. I won't make that mistake again.
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Re: Odd disk drive error

Postby Eric » Fri Jul 26, 2013 10:28 pm

Trixter wrote:
Eric wrote:
Sadly this did not fix the issue. Drive is yours if you want a spare that needs an optical sensor fixed. I have no use for a drive that can't write, nor do I want a drive that has the sensor jumpered to always OFF because that will just bite me in the ass at some point.


It's strange to think that it could be the sensor that's actually broken, but hey, these things are at least twenty-eight years old and nothing lasts forever.
I'm not gonna make any assumptions, but I'm almost sure that if it's just not dirty, that there's a chance that there's a break in one of the leads or wires.
If that's the case, I'd end up replacing the entire sensor, anyway.

If you feel like testing it, page 29 in the service manual has information on testing it.

I really hope you get this thing working.
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Re: Odd disk drive error

Postby Trixter » Fri Jul 26, 2013 10:52 pm

I had no idea there even was a service manual for the drive :-O

I cleaned it as well as I could (had to flatten a qtip with needle-nose pliers to get to the sensor) but still no dice. I could go through the procedure to see if the sensor is broken, but regardless of the result, what could I do? I have no duplicate assembly to replace it with (I know, I know, I should have held onto that prior drive!), and if the sensor DOES check out ok, I'm in a place where I have no clue what the problem is.

So I took the coward's way out: I ordered another drive from ebay. Same seller, so if this one also has some issue, I may ask for a refund.
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Re: Odd disk drive error

Postby Eric » Fri Jul 26, 2013 11:12 pm

Trixter wrote:I had no idea there even was a service manual for the drive :-O

I cleaned it as well as I could (had to flatten a qtip with needle-nose pliers to get to the sensor) but still no dice. I could go through the procedure to see if the sensor is broken, but regardless of the result, what could I do? I have no duplicate assembly to replace it with (I know, I know, I should have held onto that prior drive!), and if the sensor DOES check out ok, I'm in a place where I have no clue what the problem is.

So I took the coward's way out: I ordered another drive from ebay. Same seller, so if this one also has some issue, I may ask for a refund.

Maybe we should make a thread that has a link to every service manual and datasheet to every component inside the PCjr! Including ICs! (That can be located online, anyway)
That's actually an experiment I wouldn't mind trying out, though I'm not sure how useful it would be.

I think the manual mainly mention replacing the whole assembly because the sensor is mounted inside with glue or epoxy. It doesn't seem like it should be too hard to replace the sensor without having to get a whole new assembly, ecpecially if the glue has become brittle due to age.

Edit: Locating a replacement might be a problem, I haven't looked at any in the QumeTrak directly, but they seem like they are similar to the ones that look like dark 5MM LEDs

Edit: I'll take a close look at it in awhile.
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Re: Odd disk drive error

Postby Trixter » Sat Jul 27, 2013 1:54 pm

Eric wrote:Edit: I'll take a close look at it in awhile.


There's no need (unless this second replacement drive I have coming also has a problem).
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Re: Odd disk drive error

Postby Trixter » Wed Sep 25, 2013 9:53 pm

Eric wrote:Did you really? Hopefully you just stored it away for parts or at least saved the drivebelt in case your new drive ever needs it. :P


And, wouldn't you know, I have a drive that gets a B or C on the disk diag test because the belt is slipping. The disk rotates at an uneven speed. The timing of this failure (no pun intended) is not great as this is one of my VCFMW display machines I'm trying to get operational by tomorrow night.

Is there any way to fix a partially slipping belt? Is there any way to "tighten" it, or make the spindle easier to turn? (I tried oil on a Qume drive once, it didn't go too well; there's no way to get the oil in without a mess and without taking the drive apart). All the Qume drive maintenance manuals say "replace belt" if it is slipping, but finding a replacement belt is going to be tricky on short notice...
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Re: Odd disk drive error

Postby jharre » Thu Sep 26, 2013 7:44 am

Trixter wrote:Is there any way to fix a partially slipping belt? Is there any way to "tighten" it, or make the spindle easier to turn? (I tried oil on a Qume drive once, it didn't go too well; there's no way to get the oil in without a mess and without taking the drive apart). All the Qume drive maintenance manuals say "replace belt" if it is slipping, but finding a replacement belt is going to be tricky on short notice...


Ugh, oil? Ugh!

I'd send you the belt from this "parts" drive you sent me, but it sure won't get there tonight. What you might try is slipping a small, flat, rubber band around the flywheel (with the strobe patterns) and then putting the belt back on over the rubber band. It will increase the circumference of the flywheel slightly, but it should still work. It may be enough to snug up the belt.

Don't leave the rubber band on there and forget it - they eventually dry out and either get very hard (and hard to scrape off) or very gooey (even messier).

I have a TRS-80 model 100 3.5" portable disk drive that I used a rubber band as a belt for a while in a pinch. It worked while waiting for a real belt to arrive. Don't know if this will work for a 5.25" Qume belt, but if all else fails it's worth a try.

PM me your address and I'll mail the belt from this old drive to you.

<*> Jim
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