Troubleshooting a Heathkit H89 Floppy Drive

[neosunrise]

So I recently acquired a Heathkit H89 in very nice condition. The computer can turn on and boot into the "H" prompt. It came with a SS SD full height Siemens FDD 100-5 floppy drive. The machine has a hard sectored controller card. Whenever I entered "B" and attempted to boot from the floppy drive, the disk would start spin but the read/write head would not move at all. The LED also did not turn on. I removed the drive from the computer and completely cleaned and lubricated the moving parts. The read/write head was able to move freely when no power was fed into the drive. The shaft of the stepper motor moved fine. However, when the computer was on, I cannot move the shaft by any means. To determine if it's the computer or the floppy drive, I hooked up another floppy drive to the same controller card and it worked perfectly fine! Now pretty much I can tell it's the Siemens drive that's faulty. Where can I begin from? The LED would not turn on even when the spindle motor was running. Any input is welcome!

 

[GearTechWolf]

On the absolute off-chance it'd make a difference, have you tried disconnecting and reseating all connectors and chips?
But the most likely case is a failed component somewhere on the controller card.
I believe the stepper being frozen when the power is on is normal, as it is 'active' even when not moving, otherwise it could drift.
That's about as far as my floppy-drive knowledge goes so far. Need to attempt fixing some of my own!

 

[ldkraemer]

WOW! Heath used a lot of different floppy drives, according to their documentation.
What Manufacture and Model Floppy Drive are you referencing?

Larry

 

[neosunrise]

On the absolute off-chance it'd make a difference, have you tried disconnecting and reseating all connectors and chips?
But the most likely case is a failed component somewhere on the controller card.
I believe the stepper being frozen when the power is on is normal, as it is 'active' even when not moving, otherwise it could drift.
That's about as far as my floppy-drive knowledge goes so far. Need to attempt fixing some of my own!

I cleaned the contacts. All chips are soldered on. It’s good to know the motor is supposed to get stuck while idling. I guess it just didn’t get any pulse signal to move. Maybe I should use a oscilloscope to check.

 

[neosunrise]

WOW! Heath used a lot of different floppy drives, according to their documentation.
What Manufacture and Model Floppy Drive are you referencing?

Larry

It’s a Siemens FDD 100-5.

 

[GearTechWolf]

I cleaned the contacts. All chips are soldered on. It’s good to know the motor is supposed to get stuck while idling. I guess it just didn’t get any pulse signal to move. Maybe I should use a oscilloscope to check.

The chip at 1E (near the card-edge connector) in the picture of the board appears to be socketed.
An oscilloscope would be very helpful!

 

[ldkraemer]

A Manual for the Siemens FDD 100-5 is on Bitsavers.

http://bitsavers.trailing-edge.com/pdf/siemens/Siemens_FDD100-5_Operation_Maintenance_Mar1979.pdf

Larry

 

[retrogear]

if you move the head away from the spindle, when you power on, does it home the head back to track 0 ? If not, could be a bad track 0 sensor

Larry G

 

[Dwight Elvey]

As was mentioned, the stepper is suppose to hold position on less told to step.
The stepping is controlled by a port on the controller board, as I recall and is controlled by the processor and not a special disk controller chip.
You should be able enter the monitor and write values to the port to sequence a step instruction.
Doing that, you can debug, to determine if it is the drive or the H89 that is at fault.
Dwight

 

[ldkraemer]

neosunrise,
From Dwight's information I searched for the Port for the Floppy drives. It appears to be 0x78
from the documents.

You could go to the Monitor, and try OUT 124,1 (0x78 = 120 Decimal) and see if Floppy A: Runs.
For B: it would be OUT 124,2

If that works next step would be to issue commands to step the Floppy Drive.

REM  124 = 0x7C
REM  120 = 0x78
REM
REM
REM            0x78       0x78
REM  A1 A0     READ       WRITE      
REM   0  0     STATUS     COMMAND    78 = 120
REM   0  1     TRACK      TRACK      79 = 121
REM   1  0     SECTOR     SECTOR     7A = 122
REM   1  1     DATA       DATA       7B = 123
REM                               Drive = 124

Larry

 

[neosunrise]

The chip at 1E (near the card-edge connector) in the picture of the board appears to be socketed.
An oscilloscope would be very helpful!

1E is a resistor network for termination. It runs very hot for some reason. i have an oscilloscope but don’t know where to begin with.

 

[neosunrise]

if you move the head away from the spindle, when you power on, does it home the head back to track 0 ? If not, could be a bad track 0 sensor

Larry G

No it doesn’t Move at all. However, if i connect it to an 8088 machine, it moved once I switched to drive A.

Update: I shorted the HS and HM jumper at the same time, now when I tried to boot, the led came on, head solenoid engaged and the motor spin. I also tried to move the head away, it actually homed itself to track 0 and then stopped.

 

[neosunrise]

As was mentioned, the stepper is suppose to hold position on less told to step.
The stepping is controlled by a port on the controller board, as I recall and is controlled by the processor and not a special disk controller chip.
You should be able enter the monitor and write values to the port to sequence a step instruction.
Doing that, you can debug, to determine if it is the drive or the H89 that is at fault.
Dwight

Thanks but how to enter monitor at the H: prompt?

 

[ldkraemer]

Do you have Basic available to Peek & Poke?

Larry

 

[neosunrise]

Do you have Basic available to Peek & Poke?

Larry

I can use the “go” command to peek memory space I believe, but no, I don’t have BASIC unless I boot into the system. As I mentioned in the main post, the computer worked fine with another drive.

 

[neosunrise]

I wanted to provide an update to the drive. It seems that the previous owner used it with a couple of external floppy drives. He shorted the HS and DS1 jumpers while left MX open. After a few tries, I found that if I expected to use it as Drive A:, then DS3 (rather than DS1) should be shorted. That said, when booting from this drive, the head would move slightly back and forth for a few times and then an "Bdos Err On a: Bad Sector". I adjusted the track zero sensor but it did not help. I then ordered a same (luckily I was able to find one) drive and it worked perfectly fine on the computer! I'm assuming that something could be wrong with the read/write head - why? Because the drive acted exactly the same with and without the head connected. Regardless, I now have a fully functional H89 and I'm happy about it.

 

[ldkraemer]

I'm glad you found a replacement that was working. I haven't located any information on the
Jumpers for those floppy drives. Do you have the Jumper setting information?

Thanks.
Larry

 

[Dwight Elvey]

It might not be the head that is bad. Now that you have a working drive, you can look at things like the signals and compare them with the bad drive.
One thing that I didn't mention is that these older drives that using belts need a couple of things fixed. One is to make sure that the belt is not slipping. One can usually get more life from a slipping belt by adjusting the motor mount. The other thing that I've seen is sometimes the belt will loose some rubber that is stuck to the drive wheel or the flywheel. Make sure the surfaces are clean with no lumps. Many of the drives come with strobe wheels. If you don't have an older florescent light that flickers at 120 Hz, you can use a neon glow lamp with appropriate resistor to make a strobe light. If your drive doesn't have a strobe disk, you can get an image from somewhere on the web and print one.
Of course, I've assumed that the head was carefully cleaned. It doesn't take much gunk on the head to have problems similar to what you're seeing ( heads rarely fail on floppy drives without some visible damage). As I recall, the drives were single sided. If so make sure the pad is clean and puts even pressure on the disk ( not easy to check but can be done with a small mirror ).
Dwight

 

[neosunrise]

I'm glad you found a replacement that was working. I haven't located any information on the
Jumpers for those floppy drives. Do you have the Jumper setting information?

Thanks.
Larry

Here you go!

 

[neosunrise]

It might not be the head that is bad. Now that you have a working drive, you can look at things like the signals and compare them with the bad drive.
One thing that I didn't mention is that these older drives that using belts need a couple of things fixed. One is to make sure that the belt is not slipping. One can usually get more life from a slipping belt by adjusting the motor mount. The other thing that I've seen is sometimes the belt will loose some rubber that is stuck to the drive wheel or the flywheel. Make sure the surfaces are clean with no lumps. Many of the drives come with strobe wheels. If you don't have an older florescent light that flickers at 120 Hz, you can use a neon glow lamp with appropriate resistor to make a strobe light. If your drive doesn't have a strobe disk, you can get an image from somewhere on the web and print one.
Of course, I've assumed that the head was carefully cleaned. It doesn't take much gunk on the head to have problems similar to what you're seeing ( heads rarely fail on floppy drives without some visible damage). As I recall, the drives were single sided. If so make sure the pad is clean and puts even pressure on the disk ( not easy to check but can be done with a small mirror ).
Dwight

How do I know if the head is actually bad? Testing the resistance of the coils? Anyhow, the belt was checked and the spinning speed was adjusted as well. The head was cleaned. The pad firmly pressed the disk media to the head. Guess next step is to compare the signals on the two drives side by side using a oscilloscope.