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giobbi
July 30th, 2016, 11:37 AM
Hi All,

I just got another Osborne One, but I discovered the B: drive doesn't work. I opened it and I discovered the motor that should moves the heads doesn't spin.

I'm not sure if it's a motor problem (game over, I guess) or a controller problem (I hope!).

I would try to replace the controllers between drive A: and B: to see where's the problem, but they're slight different (rev. J vs. rev. W) and I'm afraid it would cause more issues, due to a possible incompatibility. BTW the drives, as you can see on the below pictures, are different models.

What should I check first? There is any typical issue that leads to this kind of problem?

cheers,
Giovi


32368
drive A: (good)

32369
drive B: (bad) -- don't worry about the unplugged connectors (flat cable connector and one at the bottom right corner), I removed them to raise the card.

Randy McLaughlin
July 30th, 2016, 12:07 PM
Looks like two different manufacturers (not that it matters) what you really want is what we all had in the 1970's a small stack of drives to swap whole or parts with. Used up long ago.

You can get a long cable and put a drive externally until you find an SA-400 style drive. Once you have a drive outside the case just use a variety of drive 5.25 or 3.5, yes a 1.44mb drive will hookup but you will still have the same storage.


Randy

MicrocomputerSolutions
July 30th, 2016, 12:40 PM
Yeah, it looks like two drives from different manufacturers. Swapping parts between them is not a good idea.

Your first drive looks like it's an MPI. The second looks like a Shugart SA-400.

If I were you, I'd go shopping either for a matching MPI, OR two Shugart SA-400. If you go Shugart, make sure that you get the 400L, which is 40 tracks. The earlier/original SA-400 is a 35 track drive.

giobbi
July 30th, 2016, 12:45 PM
Looks like two different manufacturers (not that it matters) what you really want is what we all had in the 1970's a small stack of drives to swap whole or parts with. Used up long ago.

You can get a long cable and put a drive externally until you find an SA-400 style drive. Once you have a drive outside the case just use a variety of drive 5.25 or 3.5, yes a 1.44mb drive will hookup but you will still have the same storage.


Randy

Do you mean I can take whatever floppy drive for PC, connect it, and it will work like the original one?

giobbi
July 30th, 2016, 12:47 PM
Before to trash the drive, is there anything I can check on the controller board? Since it's discrete component (no SMD and so on) it would be relatively easy to fix, if I know where's the problem (of course admitting it's not a motor issue)....

giobbi
July 30th, 2016, 01:30 PM
After a deep search on the web I found the controllers are quite compatible (same board, slightly different revision). So I swapped them and I found the problem is the controller and not the head motor (pheeew!)

Now what I need is to fix the controller. Any idea?

--> I found the six head motor wires lead to two ICs, SN75451... would one of them be the culprit?

Randy McLaughlin
July 30th, 2016, 01:56 PM
The most common failure are connections. Swap it back and verify it's the board.

All of the chips should be common chips that are available. If you replace a chip use a quality socket for it.

Try and determine what to replace - start with a careful visual inspection.

If you don't have a lot of experience work backwards - the drivers (75451's) first - using flush cutting dikes cut the pins off the plastic chips leaving the pins as long as possible - then grab the pins with needle nose pliers/forceps/tweezers and heat the solder joint pulling out the pins. This will reduce the chance of damaging the board - the chips are cheap - board is irreplaceable.

After the pins are removed use solder sucker to clear out the solder.

Just remember you can buy all new chips and sockets for $20 so no biggie in replacing good chips - unless you damage the board.

The part with the screw is a variable resistor use to adjust motor speed. Two easy way to adjust the speed there is PC software that tells you drive speed stick the drive in a PC and adjust - or use the pattern on the bottom of the drive with a neon light - the pattern will appear to stop @ 300rpm.


Randy

Chuck(G)
July 30th, 2016, 02:21 PM
FWIW, I've had a 75451 go bad on a drive board (it was a Tandon), so it's not impossible. They're peripheral driver ICs and so handle quite a bit of power.

ldkraemer
July 30th, 2016, 02:42 PM
With the Floppy drive Ribbon Cable removed, and the Drive powered up, you can Jumper Pin 16 (MOTOR ON) LOW and the Spindle Motor should run.
That should be a quick and easy test. All ODD Pins are NOT common, as the Osborne has +12 VDC & +5 VDC on some of the ODD Pins.

Larry

Chuck(G)
July 30th, 2016, 03:58 PM
With the Floppy drive Ribbon Cable removed, and the Drive powered up, you can Jumper Pin 16 (MOTOR ON) LOW and the Spindle Motor should run.
That should be a quick and easy test. All ODD Pins are common.


But the OP said:



I just got another Osborne One, but I discovered the B: drive doesn't work. I opened it and I discovered the motor that should moves the heads doesn't spin.

The way I read this is that the positioner/stepper doesn't move; he's not talking about the spindle motor.

giobbi
July 31st, 2016, 08:21 AM
The most common failure are connections. Swap it back and verify it's the board.

All of the chips should be common chips that are available. If you replace a chip use a quality socket for it.

Try and determine what to replace - start with a careful visual inspection.

If you don't have a lot of experience work backwards - the drivers (75451's) first - using flush cutting dikes cut the pins off the plastic chips leaving the pins as long as possible - then grab the pins with needle nose pliers/forceps/tweezers and heat the solder joint pulling out the pins. This will reduce the chance of damaging the board - the chips are cheap - board is irreplaceable.

After the pins are removed use solder sucker to clear out the solder.

Just remember you can buy all new chips and sockets for $20 so no biggie in replacing good chips - unless you damage the board.

The part with the screw is a variable resistor use to adjust motor speed. Two easy way to adjust the speed there is PC software that tells you drive speed stick the drive in a PC and adjust - or use the pattern on the bottom of the drive with a neon light - the pattern will appear to stop @ 300rpm.


Randy

Connections are ok but I will check them again. Maybe a broken joint that needs some fresh solder.
Probably on of the ICs. No problem on my side to replace ICs, I have a lot of experience about it... since I don't know how to diagnose a problem, what I usually do is a "brute force attack", I change every component, one at once, until to find the culprit. I already fix some CBM computers... I have an 3032 that's fully socketed, I replaced all the chips until I found the problem (a broken trace under an old socket a previous owner put, LOL).

-------

@Chuck: Yes, the stepper motor is the problem, not the spindle one. But I've already found the problem is the controller, the motor is ok. Since the stepper motor wires lead to the two 75451, I will start with them.