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Unique S-100 computer (Z-80/Vector Graphic/Micropolis)

deramp5113

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The CPU speed is set by jumper area A on the COU board. Both 2 and 4 MHz use the 8 MHz xtal. But if this was all working before as a system, most likely the CPU is at 4 MHz like the FDC is set.

With power off, manually rotate the head worm gear so the head is clearly not at track zero. Then run the program. Does the head move at all after you select the drive in PC2FLOP? Do you have more than one drive? Did you try both drives as an option in PC2FLOP?

Mike
 

nullvalue

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This may be helpful to know but this system was found complete with everything except for the FDC board. That I had to purchase on eBay (vintage computer museum). I have no idea as to it's condition or what system it was pulled from. It was really odd - the ribbon cable was just dangling inside the chassis. The dual drive was there - but no controller.

Yes I have the Micropolis 1053-II, which has two 5 1/4" drives. '0' spun the top drive. Curiously, '1' also spun the top drive, not the bottom as I would have expected. '2' and '3' also spun the top drive.. I will open it up and try your experiment.

Edit: The head mechanism is not moving at all. Belt & disk spins, but no head movement. Occasionally I hear a squeaking/squealing sound like something is trying to move. Could the stepper motor be seized?
 
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deramp5113

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I have not had much problem with the stepper motors (head movement) in the Micropolis drives, but it could certainly be stuck or have failed. How hard is it to manually rotate the worm gear and move the head on each drive (with power off)?

Note that the hub motor will typically spin on both when either drive is drive is accessed. The hub bearings in those Micropolis drives are often bad. Remove the belts and see how freely the hub spins on each drive.

Mike
 

nullvalue

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Thankfully, the hubs do seem to spin freely and smoothly, I don't feel any binding or grinding. With power off, I can rotate the worm gear using just my fingers fairly easily. I tried with a disk in both drives, 0-3, no options produced head movement on either drive. The squeaking sound I hear may just have been coming from the hub. On closer inspection, I don't really sense the stepper motor engaging in any way.
 

deramp5113

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Sounds like you'll have to start diagnosing drive operation then. Now that you have the unit open, do both drives spin when either drive is selected? With power applied, can you still rotate the worm gear on each drive with your fingers or does it feel like it's being held in place now?
 

exidyboy

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Edit: The head mechanism is not moving at all. Belt & disk spins, but no head movement. Occasionally I hear a squeaking/squealing sound like something is trying to move. Could the stepper motor be seized?

Through rough handling in the past the leadscrew can actually pop out. Perhaps imagine a dislocated joint. Can you see that it is seated correctly at both ends. If you send the right signals you might get a tiny amount of movement when it is in that state.
 

nullvalue

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Through rough handling in the past the leadscrew can actually pop out. Perhaps imagine a dislocated joint. Can you see that it is seated correctly at both ends. If you send the right signals you might get a tiny amount of movement when it is in that state.

I'm pretty sure it's in the right position. I took the whole thing apart, cleaned and regreased everything.
 

nullvalue

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Sounds like you'll have to start diagnosing drive operation then. Now that you have the unit open, do both drives spin when either drive is selected? With power applied, can you still rotate the worm gear on each drive with your fingers or does it feel like it's being held in place now?

Yes if a disk is in the drive, both drive hubs spin regardless of which number I enter. Yes, when power is applied, I can no longer move the worm gear.

Here are some pictures of the inside of the drive - if that helps any:

20200512_175012.jpg 20200512_175021.jpg 20200512_175233.jpg 20200512_175042.jpg 20200512_175100.jpg 20200512_175154.jpg 20200512_175914.jpg
 
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deramp5113

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Do your drives start spinning only when they’re selected and then stop after 4-5 seconds, or do they run all the time like an 8” drive? When the drive is selected by PC2Flop, do you hear the head load?

Mike
 

nullvalue

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Yes they only start spinning once they're selected, and stop spinning after about 5 seconds. I only hear the sound of the hub spinning, no head loading sounds at all.
 

nullvalue

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So I decided to go through and give everything another good cleaning. Let the ribbon cable soak with some DeOxIt on the leads and cleaned up the connectors on the drive PCB. Making some progress! Now the solenoid engages and the head snaps down. The worm gear engages and moves the head all the way to the outer edge of the disk. I can see once it reaches the edge, the 0-track switch does get engaged. However, the application is still saying "Seek to track 0 failed". Same thing happens for both drives. But now at least I can see the head only engages on the correct drive when I enter 0 or 1.
 
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deramp5113

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Great progress! Use a scope and see if the track 0 signal on the interface cable (pin 26) is getting asserted (asserted = low). Look at the signal on the drive PCB and then on the floppy controller PCB and see where it is failing. Trace backward as required to its origination on the drive PCB, and/or forward to it's final destination in the latch on the floppy controller end.

Mike
 

nullvalue

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Awesome, will do - is the track 0 signal simply asserted by that switch, or is there more involved than that?
 
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deramp5113

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nullvalue

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Well I didn't really do anything but I'm back to the head not moving at all again. For drive #1, I can fool it into thinking it found track 0 by just starting it in that position. I just wanted to test the app. Sending XMODEM data over port C seems to work because after a while, it spins up the disk and I can assume it's trying to write. Of course it fails (write failure on track 0). I can't get fool it for drive #0 though for some reason. But for now I'm back to trying to figure out why the heads won't move. The correct solenoid engages and the head snaps down.. but the steppers aren't working. I took it apart and meticulously cleaned every pin/connector and the inside of the ribbon cable. Everywhere a connection is made. Still can't get it to work again.
 

nullvalue

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I swear I may have no hair left at the end of this. For some reason it just decided to work.. head's moving.. Do you think I should replace the caps on the board? So I tried writing a disk.. tried a couple times now.. blank disk in, both drive 0 and drive 1. Once the transfer hits 52,864 bytes it starts writing. Every time I get a "Write failure on track 0, sector 7." (although the sector that fails seems to change) - any thoughts?

Edit: side question - while I do want to get the actual hardware floppy drive working, do you think it would be possible to get a Gotek working with this setup?
 
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nullvalue

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Thanks I'll check it out! But how do we know it's writing successfully and failing to read - and not just failing to write? Or would the same adjustments fix this?

Also how would I invoke the read/write operations it's talking about in tests 2.1.3 and 2.1.4?
 
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