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DeChief
March 15th, 2017, 05:24 AM
I recently got a Commodore PC 20-II for free with its keyboard, a Thompson monitor, all the cables, a mouse, and a bunch of floppies, and I've got a few questions.

How can I remove the boards? I managed to get the FDD and HDD out with great difficulty, but I can't see a way to easily remove the motherboard (/boards). I've taken the screws out, but I can see a few plastic mounting pegs under the part of the metal casing that holds the drives, and they are impossible to get to.

Additionally, the FDD won't read correctly. It read the Commodore PC 10 MS-DOS disk that it came with and booted just fine, but wouldn't read anything else. Now it won't even read the MS-DOS disk... How should I go about fixing this? Does it have something to do with capacitors? Is there some kind of floppy drive alignment guide I can use? And if I can't fix it, are regular floppy drives from the era compatible with this machine? I noticed that it's missing 2 pins on the edge connector (1 and 2 I believe), whereas the other drives I've seen have these pins (including a TRS-80 Model 4 that I picked up today, which just so happens to have a drive with the same problem as this Commodore PC).

Stone
March 15th, 2017, 05:30 AM
Have you tried cleaning the drive's heads with a cleaning disk and solution? If not, that should always be your first step as floppies are notorious for fouling drives' heads, especially since the disks are all now very old.

It sounds like the boot disk was OK but the next disk you inserted hosed the drive, thus preventing further use of it.

Scali
March 15th, 2017, 05:35 AM
Commodore used its own floppy controller, based on the Amiga one. This has slightly different wiring and different requirements for floppy drives than the common IBMs and clones (the Commodore is closer to the Shugart interface).
In short, it has to do with how motor on and drive-select work. I believe the Commodore only drives the 'drive select'. There are certain drives that have a 'motor on on drive select' jumper. That's the sort of drive you need.
If you connect a 'regular' drive, you'll probably find that the drive led comes on (because that works on 'drive select'), but the motor doesn't spin up (because Commodore doesn't drive that line specifically).

There is also no 'cross-wiring' between the A: and B: drives on the cable, so you do that with jumpers as well (common IBMs and clones configure all drives as 'drive 1'/B:, and the twist in the cable reverses the signals, so the drive after the twist is actually A:, even though it is jumpered to B:).

DeChief
March 15th, 2017, 05:54 AM
Commodore used its own floppy controller, based on the Amiga one. This has slightly different wiring and different requirements for floppy drives than the common IBMs and clones (the Commodore is closer to the Shugart interface).
In short, it has to do with how motor on and drive-select work. I believe the Commodore only drives the 'drive select'. There are certain drives that have a 'motor on on drive select' jumper. That's the sort of drive you need.
If you connect a 'regular' drive, you'll probably find that the drive led comes on (because that works on 'drive select'), but the motor doesn't spin up (because Commodore doesn't drive that line specifically).

There is also no 'cross-wiring' between the A: and B: drives on the cable, so you do that with jumpers as well (common IBMs and clones configure all drives as 'drive 1'/B:, and the twist in the cable reverses the signals, so the drive after the twist is actually A:, even though it is jumpered to B:).

Thanks for the info! It seems the rabbit hole of proprietary computer hardware deepens the more I read about it... Still, nothing could be worse than IBM and their edge connectors :mad:


Have you tried cleaning the drive's heads with a cleaning disk and solution? If not, that should always be your first step as floppies are notorious for fouling drives' heads, especially since the disks are all now very old.

It sounds like the boot disk was OK but the next disk you inserted hosed the drive, thus preventing further use of it.

Funny you should mention a cleaning disk; I just got a brand new one with the TRS-80 I picked up today. Is it safe to assume that the cleaning solution is still alright, or does that kind of thing not live far past its expiration date? I cleaned the read head with some IPA, but haven't tested the drive again yet because it's almost 1am and my eyes are half closed already.

I should clarify that the boot disk didn't read at first, but worked after taking the disk out and putting it back in a few times.

RuudB
March 15th, 2017, 06:10 AM
I've taken the screws out, but I can see a few plastic mounting pegs under the part of the metal casing that holds the drives, and they are impossible to get to.
I have one and disassembled it once but that was three years ago. But IIRC it was just taking the screws out, sliding the board a bit to the left, lifting it up a bit and move it to the left out of the case. And IIRC taking it out wasn't a problem, placing it back again was.

I can only wish you good luck!

Stone
March 15th, 2017, 07:14 AM
Funny you should mention a cleaning disk; I just got a brand new one with the TRS-80 I picked up today. Is it safe to assume that the cleaning solution is still alright, or does that kind of thing not live far past its expiration date? I cleaned the read head with some IPA, but haven't tested the drive again yet because it's almost 1am and my eyes are half closed already.I believe that the cleaning solution is IPA.

DeChief
March 15th, 2017, 10:38 PM
I have one and disassembled it once but that was three years ago. But IIRC it was just taking the screws out, sliding the board a bit to the left, lifting it up a bit and move it to the left out of the case. And IIRC taking it out wasn't a problem, placing it back again was.

I can only wish you good luck!

I managed to get it out and back in again fairly easily, thanks for the tip.


I believe that the cleaning solution is IPA.

Although not exactly a scientific method, I gave the cleaning solution and my IPA a good whiff and they smelt identical, so you're probably right. I fired up the PC and used the cleaning floppy with some IPA, but it didn't seem to change anything. Although after several dozen tries of using the boot disk, it fired up DOS once but would give me a read error when I tried "dir". Same with every other floppy I tried. I also tried another DOS disk I have with the same results.

I did notice something though: whenever I put a floppy in and close the latch (or rather, push the button. It's a bit of an odd mechanism...), the floppy doesn't exactly spin properly, it looks quite wobbly. I guess the best way to describe it is that it's like one of those spinning plates on a stick, where the plate is spinning but it's also gyrating around the stick and not staying with its centre directly on the stick. But sometimes it spins correctly, and on the off chance that the boot disk does work, it's when it's spinning correctly (although the disk spinning correctly does not automatically mean that it will boot).

So now what?

archeocomp
March 16th, 2017, 12:27 AM
I did notice something though: whenever I put a floppy in and close the latch (or rather, push the button. It's a bit of an odd mechanism...), the floppy doesn't exactly spin properly, it looks quite wobbly. I guess the best way to describe it is that it's like one of those spinning plates on a stick, where the plate is spinning but it's also gyrating around the stick and not staying with its centre directly on the stick. But sometimes it spins correctly, and on the off chance that the boot disk does work, it's when it's spinning correctly (although the disk spinning correctly does not automatically mean that it will boot).

So now what?
This has been asked here by user Romanon a year ago or so and I do not know if he has found a solution. The best would be to replace the wobbly part.

http://www.vcfed.org/forum/showthread.php?54306-FDD-YD-580-holding-shake&highlight=

DeChief
March 16th, 2017, 12:55 AM
This has been asked here by user Romanon a year ago or so and I do not know if he has found a solution. The best would be to replace the wobbly part.

http://www.vcfed.org/forum/showthread.php?54306-FDD-YD-580-holding-shake&highlight=

So where would be the best place to get a new "cone"? I might be able to cobble together a model and 3D print it, do you think that would work?