Fixing Floppy-Drives

[Bryce]

Just a quick update on the latest two patients: No. 1 was a relatively easy fix: Remove old belt gunk, re-solder a few dry joints, calibrate rpms and re-align head. Now fully and reliably working again.
Unfortunately No. 2 really is in a sorry state. There is serious corrosion on the PCB, most likely water damage. It looks bad, but all connections seem to be still there. There's also quite a lot of rust on the metal parts. It also seems to have had some extensive repair work done in the distant past (not done by Dataserve), the cable to the head has been replaced. I can get the rpms stable at 300, but the head mechanism is badly worn and the head has quite a bit of "wiggle", meaning that it rarely lines up to the same point twice. I have tried every tweak I can think of and will completely dis-assemble and rebuild the drive over the next few weeks, hopefully with some spare parts that I hope to get from a destroyed drive, but I don't hold up much hope for it. Looks like I may be looking at the first ever drive that I couldn't manage to fix

Bryce.

@Gryzor: The owner did get a refund for the "attempt", but he was still left with the bill for shipping two drives to the UK and back.

[CanonMan]

No. 1 was a relatively easy fix: Remove old belt gunk, re-solder a few dry joints, calibrate rpms and re-align head. Now fully and reliably working again.

I hope you don't mind me asking, but what tools/procedure do you use to realign the head?


I had a couple of drives that had all the other bits you mention done to them, but they were still not reading reliably. Maybe I should dig them out (if I haven't already binned them!) and have another look at them.

[Bryce]

I hope you don't mind me asking, but what tools/procedure do you use to realign the head?


I had a couple of drives that had all the other bits you mention done to them, but they were still not reading reliably. Maybe I should dig them out (if I haven't already binned them!) and have another look at them.

All drive repairs are done with an oscilloscope, a screwdriver, the DSKTest software, "tongue at the right angle" and lots of experience.

I really hope you haven't dumped good drives because of a badly aligned head!

Bryce.

[CanonMan]

All drive repairs are done with an oscilloscope, a screwdriver, the DSKTest software, "tongue at the right angle" and lots of experience.

I really hope you haven't dumped good drives because of a badly aligned head!

Bryce.

Do you have the proper alignment disk? That's the only thing that's holding me back, I've got a scope and all the other bits!

[||C|-|E||]

All drive repairs are done with an oscilloscope, a screwdriver, the DSKTest software, "tongue at the right angle" and lots of experience.

I really hope you haven't dumped good drives because of a badly aligned head!

Bryce.

In my experience, the position of the tongue is absolutely essential for most of the repair works. I employ the technique all the time, and it is the same when parking the car.

[Bryce]

Do you have the proper alignment disk? That's the only thing that's holding me back, I've got a scope and all the other bits!

No, I just use a selection of commercial game disks. If you line it up to those you know it will work with disks from any other drive that's properly aligned.

Bryce.

[tjohnson]

Looking for a bit of assistance.  I have replaced the belt in my drive on my new (to me) 6128, it had gone all horrible and sticky, it now spins the disc nicely but unfortunately the read head is not moving at all, it doesn't make any horrible noises at all and doesn't appear to attempt to move and I get a "bad command" returned when running CAT etc.  I wonder if this was the reason the computer was retired off some years back.  I have done some very basic checks and the monitor is delivering a fraction under 12v (11.9v) at the pcb header onto the mainboard (not the FDD).  Ive had a quick look at the service manual and it doesn't seem to give a great deal of info on the FDD other than replace it  The FDD board looks in good physical order no obvious corrosion, reading through this thread looks like I need to examine the PCB for dry solder joints.  The drive is an EME-155.  Can anyone give any hints on what to check next.

[Bryce]

I'd definitely check for dry joints on the power connector on the drive PCB and then on the connector that goes to the drive head motor. Both of these are known for dry joints and would give the results you're observing.

Bryce.

[tjohnson]

Thanks Bryce, had a look tonight, the solder joints look ok to me, couple maybe aren't 100%, what I did notice is a small bit of plastic by the electrolytic capacitor by the power connector right at the bottom.  In my photo you can still see a tiny bit.  I'm wondering if this has failed and could be causing the issue. 

[Audronic]

Bottom Photo (FDD 1.jpg) Pin 1 on CN5 is suspect ?


Ray

[Bryce]

Yup, CN4 probably isn't great either. These could be your problem.

Bryce.

[tjohnson]

Yeah thanks both, now its morning and not the middle of the night I've taken a good look at CN3, CN4 and CN5 as you've both pointed out, they are quite shallow and have little solder on them, and all three appear to have suspect joints.  Will fire up the soldering iron later and fingers crossed, would be fantastic to get the drive working again.

[tjohnson]

Soldering done, unfortunately no change.  Disc spins but the head stays stationary.  damn.

[Bryce]

What equipment have you got to make further measurements?

Bryce.

[tjohnson]

Unfortunately not a lot, i have a Multimeter but nothing more advanced.  What would be your next steps?  I have a friend who may be able to help with additional test equipment.

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[Bryce]

The next step would be to follow the signals:

- Check if step signals are being sent from the FDC, then to the output logic, then to the STEP pin of the floppy drive and and finally what signals are going to the motor.

That way you can find out where it's going wrong.

If you don't have the equipment or knowledge to do this, you can send me the drive for repair.

Bryce.

[tjohnson]

Hi Bryce thanks for the advice again,  I've ordered a logic probe which might help me check that is going on as you suggest.  I looked at the circuit diagram for the seek and direction pins on the fdc and can see they are going through a couple of logic gates.  I figured the price would allow me to check whether they are going high low or pulsing and whether there is anything stuck and the probe is cheap so not alot to lose.   Thanks for the offer of repair it may come to that.  If i had another drive at least it would confirm if the signal is arriving from the fdc and that the fault is on the drive.

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[tjohnson]

Hi all,
well the latest on the drive is some progress.  I got the logic probe and I believe the signals are all ok, with the seek signal activating when running cat and have also checked the AN8250N on the floppy pcb and it appears to respond correctly on the signal pins as far as can tell from the probe.  I didn't check the voltages going to the actual motor, looking at the data sheet from the AN8250N I'm not sure I can test that with the equipment I've got other than to check the resistance between the pins.


However what I have found is that the stepper motor is showing signs that it is trying to move so now I'm suspecting that the stepper is actually jammed - I have uploaded this video to youtube to show what is happening. 
https://www.youtube.com/watch?v=2QDcFbfdB6c


I can find some useful post from Bryce where he took apart a stepper motor and repaired it, what isn't clear is whether this was the same kind of failure and wether what I'm seeing is a jammed stepper or something else.
Cheers Trevor 

[tjohnson]

Little bit more tinkering and almost there.  I rotated the shaft a few times and now its moving, hopefully just needed a bit of encouragement to get it going again.  I'm feeling a bit happier about this now!


I've now got it reading discs however it is not quite right yet, for example on the game Tomahawk it will load the loading screen but then keeps tracking to the same spot over and over.  I've had a bad read error.  I'm now hoping this is a process of calibration which I'm hoping that Bryce can tell me how to calibrate.


Right now time for bed, it is way to late to be tinkering with my childhood computer on a school night.

[Bryce]

You may just need to give the motor some time to come back, it may still be sticking at some points and need some more lubrication. The drive where I needed to fix the stepper motor had a broken bushing. If yours had the same problem it wouldn't be reading disks at all.

Bryce.

[tjohnson]

Cheers Bryce. I couldn't resist as further test this morning and seemed to have improved overnight and fully loaded the test disk but looked like it stuck a couple of times.   Maybe a bit of use will loosen it up.  Is there anyway lube the internals a bit as it sounds a little squeaky when moving by hand?

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[Bryce]

Not really. The problem is, if you remove or even loosen the stepper motor the entire drive will need to be recalibrated.

Bryce.

[Audronic]

@tjohnson

You could put a small drop of sewing machine oil at the both bearing ends (On the bearings)

Ray

[tjohnson]

Cheers, will give that a go.  The drive doesn't seem too bad, I tried a number of disks and couple got read errors that may be the disk more than the drive.   Want to try and get some diagnostic programs on there to check rotation speed so I need to expedite my 3.5"  connection to do so.
Cheers Trevor

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[tjohnson]

So I thought I'd update this on the latest on returning my disk drive back to working order.  I found the drive very temperamental and definitely wasn't working right seemingly have read errors on the majority of the disks I have, that just couldn't be right.  I managed to measure the rotation speed and it was pretty much spot on 300rpm so that didn't appear to be the issue.  The head was cleaned but what I noticed was the little felt pad on the spring arm was worn and out of shape, not flat.  I pulled what was left off and glued some replacement material on -a couple of small bits of cleaning glass lense cloth.  I also marked the stepper motor and released the screws so I could do some calibration and know generally where I started.  Anyway the final upshot is now that it reads disks it couldn't before and seems to be fully working again, finally.  It has taken me a lot of time messing around but I'm pleased the original drive is now working correctly again.  I think the main issue was the felt pad, I guess that helps to apply pressure to ensure the disk surface is flat to the read head but with it out of shape the pressure would have been off.