restoring a battery-bombed IIcx

[Phipli]

I forgot to say - yes I've tried three different cables, including one which has the -12V wire physically severed, just in case that were a problem.

From a discussion here last year: https://68kmla.org/bb/index.php?threads/800k-floppy-eject-motor-off-the-chain.40403/#post-437182


I also forgot that I did this teardown of a gearbox only two years ago: https://www.bigmessowires.com/2021/08/12/eject-motor-gearbox-autopsy/

That quote might not be correct because the motors work outside the chassis. Unless they mean a microswitch inside the motor assembly, in which case that's fine, except that the alignment is just to ensure it correctly hooks the eject mechanism, not because of the microswitch.

 

[volvo242gt]

Microswitch is under the board shown next to the eject motor.

 

[Phipli]

Microswitch is under the board shown next to the eject motor.
View attachment 64632

Yes, part of the motor assembly. That means it doesn't work how the quoted text says, otherwise the motors wouldn't happily do 180° then stop when outside of the floppy drive, like they do.

 

[volvo242gt]

Yes, part of the motor assembly. That means it doesn't work how the quoted text says, otherwise the motors wouldn't happily do 180° then stop when outside of the floppy drive, like they do.

Exactly. The pin position is what tells the motor to shut off, not the floppy drive's mechanism's position.

 

[bigmessowires]

I remember how this works now. There's an oblong shaped foot on the bottom side of the gear with the metal pin, and this physically pushes the microswitch open, cutting off the power to the eject motor. Then when you insert a new disk, it moves the gear and the switch makes contact again. You can verify this with a meter and a disassembled gearbox: check for continuity between the brown and yellow wires. In one gear position there will be continuity, but keep turning the gear and the circuit will break. Try inserting and manually ejecting a disk, and check for continuity between yellow and brown in each state.

I fully disassembled the gearbox, checked the microswitch, reassembled, and tested the make/brake behavior with a meter while turning the gear. All seems good. Yet when I put everything back together, the motor still spins continuously as long as the computer is turned on.

I think I need to find a schematic for this eject circuit. I don't know if the yellow and brown wires are the actual power for the motor, or just a signal used by a transistor or other circuit that turns on the power for the motor. If those wires are the actual power then I don't understand how it's possible for the motor to run continuously, since its own motion brakes the microswitch.

 

[bigmessowires]

This is from the 800K drive, but I would guess the eject mechanism is virtually identical:

 

[bigmessowires]

I took some measurements. I think the red wire on the eject motor assembly is ground, yellow is +12V, and brown is the eject signal.

The purpose of the yellow wire and the microswitch is to automatically run the eject motor when power is turned on, until it gets to the home position and the nub on the gear pushes the microswitch open. This is a simple homing behavior that doesn't require any control logic. If the gears are physically broken so they can't turn, or the microswitch can't be pushed open, then the motor will run forever. But that's not what is happening here.

I measured a continuous 12V at the brown wire (and also the yellow wire, just in case I've confused them). That means the drive's control logic is continuously telling the eject motor to run. This might happen if Q7 went bad and were always on, or if the input to the base of Q7 were screwed up due to other component damage, or if Q6 were malfunctioning, or if the controller chip itself (not shown here) were malfunctioning.

I did a close visual inspection of all these components looking for damaged traces, but everything looks OK. The main problem with this floppy drive was that it was covered in dust and goo, but after cleaning I couldn't see any damage. I'm going to give it an extra good cleaning with alcohol and see if that helps. If that doesn't help, I could try swapping in the eject motor assembly from another drive just to be 100% certain it's not a problem with the eject motor assembly. After that I suppose I could start tracing out the circuit and verifying connections, or try replacing the transistors, or probing internal signals while the drive runs, but I don't think my interest in this runs that deep. I already have a spare drive that works, so this is just a good-faith effort to service the flaky drive before I give up on it.

 

[volvo242gt]

I took some measurements. I think the red wire on the eject motor assembly is ground, yellow is +12V, and brown is the eject signal.

The purpose of the yellow wire and the microswitch is to automatically run the eject motor when power is turned on, until it gets to the home position and the nub on the gear pushes the microswitch open. This is a simple homing behavior that doesn't require any control logic. If the gears are physically broken so they can't turn, or the microswitch can't be pushed open, then the motor will run forever. But that's not what is happening here.

I measured a continuous 12V at the brown wire (and also the yellow wire, just in case I've confused them). That means the drive's control logic is continuously telling the eject motor to run. This might happen if Q7 went bad and were always on, or if the input to the base of Q7 were screwed up due to other component damage, or if Q6 were malfunctioning, or if the controller chip itself (not shown here) were malfunctioning.

I did a close visual inspection of all these components looking for damaged traces, but everything looks OK. The main problem with this floppy drive was that it was covered in dust and goo, but after cleaning I couldn't see any damage. I'm going to give it an extra good cleaning with alcohol and see if that helps. If that doesn't help, I could try swapping in the eject motor assembly from another drive just to be 100% certain it's not a problem with the eject motor assembly. After that I suppose I could start tracing out the circuit and verifying connections, or try replacing the transistors, or probing internal signals while the drive runs, but I don't think my interest in this runs that deep. I already have a spare drive that works, so this is just a good-faith effort to service the flaky drive before I give up on it.

Pop the spare into the IIcx, call it good, then revisit the flaky drive later. Suspect something got blown on the board, which is causing the motor to keep running. I had the opposite thing occur with a MP-F75W that accidentally bumped the chassis of my old Plus while said computer was turned on. Got the usual flupping sound from the analog board. Drive worked fine afterward, but would not eject disks at all. Motor wouldn't turn on.

Once you have the flaky drive working, find an A9M0106 and swap it into that. You'll have an unmarked G7287 SuperDrive.

 

[bigmessowires]

Pop the spare into the IIcx, call it good, then revisit the flaky drive later.

I was going to do that, but I fixed the original floppy drive! Believe it or not, the continuous eject motor problem was cured by dousing the drive's controller PCB in alcohol and scrubbing it with an ESD-safe brush. I thought that had a low probability of success, but I was wrong. There must have been some invisible residual conductive goo from the battery bomb, and the alcohol scrub cleaned it away.

After that the eject mechanism behaved normally and the drive mostly worked, but sometimes struggled to read disks, detect disks, or eject disks. I cleaned the head and lubed everything, and finally got it working 100 percent for 800K disks but it wouldn't read 1.44MB disks. When I inserted a 1.44MB floppy it would offer to format it as single or double sided, which told me the Mac thought it was a double-density disk rather than high density. There's a tiny switch on the drive that gets pushed down for double-density disks but not for high-density disks, so the drive can detect the media type. I used a meter to verify that the switch was working OK. So it had to be a problem with the chip or circuit that reads the switch state.

Back for another alcohol scrub! This time I concentrated on really cleaning the PCB area near the front of the drive where the switches are. I scrubbed for a few minutes, used a hair dryer to dry everything up, then tried again with some 1.44MB disks. Success! Score two points for floppy drive fixes with a simple alcohol clean-and-scrub of the PCB.

 

[Phipli]

I was going to do that, but I fixed the original floppy drive! Believe it or not, the continuous eject motor problem was cured by dousing the drive's controller PCB in alcohol and scrubbing it with an ESD-safe brush. I thought that had a low probability of success, but I was wrong. There must have been some invisible residual conductive goo from the battery bomb, and the alcohol scrub cleaned it away.

After that the eject mechanism behaved normally and the drive mostly worked, but sometimes struggled to read disks, detect disks, or eject disks. I cleaned the head and lubed everything, and finally got it working 100 percent for 800K disks but it wouldn't read 1.44MB disks. When I inserted a 1.44MB floppy it would offer to format it as single or double sided, which told me the Mac thought it was a double-density disk rather than high density. There's a tiny switch on the drive that gets pushed down for double-density disks but not for high-density disks, so the drive can detect the media type. I used a meter to verify that the switch was working OK. So it had to be a problem with the chip or circuit that reads the switch state.

Back for another alcohol scrub! This time I concentrated on really cleaning the PCB area near the front of the drive where the switches are. I scrubbed for a few minutes, used a hair dryer to dry everything up, then tried again with some 1.44MB disks. Success! Score two points for floppy drive fixes with a simple alcohol clean-and-scrub of the PCB.

View attachment 64678

You might want to grease it a bit more in these areas, stock they have enough to see.

Excellent work! Glad it's working.

 

[bigmessowires]

I made a mistake lubricating the drive. I didn't have any grease handy so I used the petroleum oil that I'd bought to lubricate the fan bearing. It worked, but it's thin and runny and it has dripped everywhere outside and inside the drive. It's not water so it's not going to evaporate either. I keep wiping up little drips and thinking that must be the last of it, but then there's more.

 

[Phipli]

petroleum oil

Take care - I never use petroleum family oils in computers. They can damage plastics.

I use silicone oil as a light oil and white lithium grease for most of this sort of thing. I have various other options in the shelf too, but not needed for the floppy drive.

 

[bigmessowires]

I think it's petroleum, but I may be wrong. It's the sewing machine oil that you'd suggested a while back for the fan bearing. This is what I bought: https://www.amazon.com/dp/B000YZ1Y06 I have some white lithium grease around here somewhere, but I couldn't find it when I needed it.

 

[Phipli]

It's the sewing machine oil that you'd suggested a while back for the fan bearing.

I'll have said silicone sewing machine oil, although it won't have mattered in the motor so much.

The oil I use is synthetic - a different thing with the same application.

 

[Phipli]

Looking at what is available, it most frequently is sold as "treadmill" silicone oil these days. Hopefully it has a similar viscosity to what I use.

They use it with the treadmills because it doesn't damage the rubber.

 

[bigmessowires]

I'll have said silicone sewing machine oil

Indeed you did! I will keep digging for that white lithium grease.

After all the speculation about the letters and numbers that were carved into this Mac's motherboard, hard to read and interleaved through pre-existing silkscreen numbers, today I took a proper look at the rear of the IIcx for the first time. I'd been running the motherboard outside the case, so I hadn't noticed this rather more obvious version carved right in the middle:

 

[Phipli]

Indeed you did! I will keep digging for that white lithium grease.

After all the speculation about the letters and numbers that were carved into this Mac's motherboard, hard to read and interleaved through pre-existing silkscreen numbers, today I took a proper look at the rear of the IIcx for the first time. I'd been running the motherboard outside the case, so I hadn't noticed this rather more obvious version carved right in the middle:

View attachment 64688

I have to admit I'm very jealous of how not rusty metal stays in your part of the world.

@cheesestraws @joshc look how shiny that video card is. Bet he does't even have to sand it to get a good ground connection

 

[mdeverhart]

I will keep digging for that white lithium grease.

@LaPorta (I think) identified this as the modern version of the grease originally used on these drives. I’ve used it in a few drive rebuilds, and others swear by it:

Molykote EM-30L​

Amazon.com

 

[Phipli]

Just to be clear, different greases were used in drives at different times and places. I have drives that visibly came with white lithium grease from factory (others that didn't). White lithium grease does the job, is easier to get and is cheaper.

 

[mdeverhart]

different greases were used in drives at different times and places

Fair enough