restoring a battery-bombed IIcx

[bigmessowires]

Yes I was thinking the same thing about the higher address line. From the schematic, it's the 74F258 closest to the capacitors that's responsible for that, so it might make sense. I'll investigate.

After 10 minutes with a hair dryer pointed at the sound chips, now it's working. At first I thought the front speaker wasn't working, but I didn't have it plugged in correctly.

 

[Phipli]

The sound is good from the headphone jack. But after 10 minutes with a hair dryer pointed at the sound chips, now I'm not getting any sound from the front speaker. Either the traces feeding it have become damaged, or the headphone jack is damaged or has water inside. I think it's designed to cut off the front speaker when headphones are inserted, so maybe it thinks they're inserted even when they aren't.

This suggests either a dry joint in the sound circuit (heat lifting a chip leg), or dirty contact inside the sound jack. Spray deoxit in the sound jack and do a couple of dozen cycles with a jack to try to clean the contact.

If that doesn't sort it, poke chips in the sound circuit and see what makes a difference.

 

[bigmessowires]

The sound is OK now, I edited my post while you were replying... sneaky.

Oh ho yes, the connection between A22 and the 74F258 at location UH3 is broken, which means that 4MB RAM SIMMs can't work in bank A. I need to find the best place to run a patch wire, though. I can't find where the original trace is or where it's broken, so I'll run a wire chip-to-chip, but the closest place I can find to connect a wire to A22 is way over by the NuBus slots. I'd rather not solder a wire directly to the CPU itself. I'm not sure if I also need to check A23, A24, A25, because they are connected to UH3 but not anywhere else that I can find on the schematic.

 

[bigmessowires]

I repaired A22 by running a wire to the ROM SIMM socket, and verified A23, A24, and A25 are OK (found them on the VGC). But I still get chimes of death when booting with the 4 x 4MB RAM in bank A. I even tried a different set of 4 x 4MB to make sure it wasn't something about those specific RAM SIMMs. I thought for sure that fixing A22 was going to fix it, bummer. I already verified the connections are good for RAA10 and RAA11 from UH3 through the resistors to the SIMM sockets.

This is testing while 4 x 1MB are installed in bank B. Strangely, I can't remove those SIMMs. They seem slightly thicker than normal and were tight when installing, now they won't pull loose.

Either the way I've divided memory between banks A and B is wrong, or there's something else broken here that I'm not seeing. Maybe this is just going to be an 8MB system.

 

[bigmessowires]

Measure twice, cut once: I had run my patch wire to the wrong pin on the ROM SIMM socket. I fixed that and it's now booting with 20 MB RAM!



We are done here. Time for a celebratory beer.

 

[jmacz]

Congrats a second time @bigmessowires !

 

[joshc]

Really nice work on this one. The IIcx is a nice machine for System 6 fun.

 

[Phipli]

Excellent work again.

I can't find where the original trace is or where it's broken

If you decide you want to try to narrow down the break, max1zzz reverse engineered the IIcx board. It will tell you where your trace goes exactly. Just open the Gerbers in a viewer.

GitHub - max234252/MacIIcx_Reloaded: 1:1 Reproduction of the Mac IIcx PCB

1:1 Reproduction of the Mac IIcx PCB. Contribute to max234252/MacIIcx_Reloaded development by creating an account on GitHub.

github.com

 

[bigmessowires]

I tried out the IIcx's original floppy drive for the first time. It was in pretty sad shape - see the photo in the first post. When powered on, it continuously runs the eject motor. Normally when I hear that symptom, I think of compact Macs and the red stripe cable / yellow stripe cable issue, but I don't think that's the issue here. Some kind of failure or damage in the floppy drive itself is causing the eject motor to run. Fortunately I have a spare drive that I can swap in, but I'll look more at this.

 

[Phipli]

When powered on, it continuously runs the eject motor. Normally when I hear that symptom, I think of compact Macs and the red stripe cable / yellow stripe cable issue, but I don't think that's the issue here.

This is caused by a failed gear in the eject motor gearbox. You can buy 3D printed replacements on eBay.

 

[Phipli]

Two screws (blue) and a cable (blue/green) to unplug. When you lift it out, you'll see it has a metal lid on the other side of the gearbox, which can be unclipped. The yellowish coloured gear usually fails, yours is likely missing teeth.

Oh, and while you're in there, don't lift the head too high, they can be over extended.

Good chance to clean the heads, relube the eject mechanism and put some grease in the rails and worm drive for the heads.

 

[bigmessowires]

I have a bunch of spare gears, and have done this gear replacement before, but I've never seen this symptom. I thought the symptom of a failed gear was that it would struggle or fail to eject a disk? This is a little different - it is constantly running the eject mechanism from the moment the power is turned on. I can try the gear replacement and see if it helps, but I'm not sure why the eject motor is running at all.

 

[Phipli]

I have a bunch of spare gears, and have done this gear replacement before, but I've never seen this symptom. I thought the symptom of a failed gear was that it would struggle or fail to eject a disk? This is a little different - it is constantly running the eject mechanism from the moment the power is turned on. I can try the gear replacement and see if it helps, but I'm not sure why the eject motor is running at all.

Struggling to eject is a symptom of a dead motor, stuck mechanism or bunged up gearbox usually. I usually fix this by cleaning things and relubricating.

A failed gear results in constant running because the peg on the motor can't return to the home position.

 

[bigmessowires]

I think it's probably a different cause with this one. I disassembled the gear box, replaced the gear that usually breaks (although it looked OK), and adjusted everything so the gears are moving smoothly. I also lubricated the mechanism and removed a tremendous amount of dust from all around the drive. The drive still runs the eject motor continuously, as soon as power is turned on.

Now that I think about it, there must be a sensor or switch that detects when the eject motor has returned to the home position and turns it off. Quite possibly this sensor is broken. I'll look for that.

 

[Phipli]

I think it's probably a different cause with this one. I disassembled the gear box, replaced the gear that usually breaks (although it looked OK), and adjusted everything so the gears are moving smoothly. I also lubricated the mechanism and removed a tremendous amount of dust from all around the drive. The drive still runs the eject motor continuously, as soon as power is turned on.

Now that I think about it, there must be a sensor or switch that detects when the eject motor has returned to the home position and turns it off. Quite possibly this sensor is broken. I'll look for that.

I don't know why, but I've seen warnings that you need to place the pin back in the rest position manually. Other people have said this, but it makes no sense to me, because as far as I understand, you pin out of position will just cause the motor to run until it returns to position? Unless I'm missing something? - EDIT - getting the pin in the wrong place would mean it wouldn't engage with the eject mechanism, but I think it would just jam if you did this, not run forever. /EDIT

Otherwise, yes, I'd check the... switch or light gate - whatever it is - that interfaces with the pin on the outside of the gearbox. Continuous running really sounds like it is either failing to return to the home position, or failing to detect the home position.

I forget, did you say you tried a cable from another machine? They're just straight through standard, IDC to IDC cables, so easy to make up. The one in my IIx is home made.

 

[Phipli]

Hum. I just dismantled a drive. There is no external sensing of the peg position. It just hooks on the eject mechanism. So I guess, make sure it is engaged with the eject mechanism.

I can't really see if the gear with the pin interacts with the PCB on the other side, but it may do. If it does, there might be brushes running on copper on the PCB that aren't conducting properly. Perhaps a little squirt of deoxit in there??

I'm not sure at all. I'm reluctant to take a working motor assembly apart more and haven't needed to before.

 

[bigmessowires]

It just hooks on the eject mechanism.

Doesn't it need some kind of feedback to know when to turn off the motor? Or does it just run the motor for a fixed period of time and then assume it worked?

there might be brushes running on copper on the PCB that aren't conducting properly. Perhaps a little squirt of deoxit in there??

Something like that would make sense... I'll look.

 

[Phipli]

Doesn't it need some kind of feedback to know when to turn off the motor? Or does it just run the motor for a fixed period of time and then assume it worked?

I just mean it isn't monitoring the pin like I had assumed. It's either monitoring the deck height / eject mechanism position, or is internal to the motor.

 

[Phipli]

Something like that would make sense... I'll look.

I've time linked to where they fix your likely specific issue.

 

[bigmessowires]

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

did you make sure the external "pin" was aligned properly? That pin trips a microswitch, which shuts the motor off. If not properly aligned, it could be your issue. I don't have to hand exactly how it's supposed to be aligned, but I believe with the drive mechanism in "ejected" state, the "pin" should be toward the front (farthest away from the rear) of the floppy. To align the pin, you need to remove that gear that was disintegrated, rotate the mechanism, then put that gear back in...

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/