Macintosh Classic II - Mistake during recap

[surfer150]

I got a Macintosh Classic II with the checkerboard issue. After i recapped the logic board, everything worked fine. Shortly after that, I decided to recap the analog board and the floppy drive too. Most capacitors on the analog board were already leaking.

During the recapping of the floppy drive, I made a mistake. I soldered in 1 uF instead of 0.47 uF and 10 uF instead of 1 uF.

When turning the Mac on with the floppy drive connected, there’s only a rattling and squeaky noise coming from the floppy drive, nothing else. No fan, no chime, no screen, no HDD. It seems like something is shorted.

When i disconnect the floppy drive from the logic board, the computer turns on, the chime plays, the HDD begins to spin but after a few seconds the HDD turns off. It does not even try to read any data from the HDD. After 30 additional seconds the missing operating system symbol (blinking floppy) appears.

I also can’t boot from the ROM using Cmd + Option + x + o.

After that, I replaced the wrong capacitors in the floppy drive, but the issue still persists. Not turn on at all when floppy drive is connected and turning on but no boot from HDD when floppy is disconnected.

Have I fried the logic board?

 

[mdeverhart]

I doubt you’ve fried the LB. There’s a lot that needs to work right in order to get to the point where it shows the blinking question mark floppy, so that’s a really good sign.

A few guesses:
1. The floppy probably has a short somewhere, likely introduced when you recapped it. A short on the floppy drive’s power rails could easily cause the power supply to go into overcurrent mode and shutdown, which would explain why it doesn’t do anything when the floppy is plugged in. Double check all of your work, looking for any obvious shorts. You may need to remove the new caps and inspect underneath them - it’s definitely possible to bridge the pads underneath the new cap. If you have a multimeter, check the resistance across one of the new caps before you remove them.

2. It sounds like the hard drive probably has the head mechanism stuck against the rubber bumper internally. This is a common problem with these old hard drives - the bumper gets gummy with age, and the head can’t un-stick itself at startup. There are a bunch of threads around here on various fixes for different models. The behavior you’re seeing is a textbook case - the drive spins up, you may here some soft ticking as it tries to move the head arm, and then it spins back down when the head fails to move.

I can’t explain why the ROM boot is failing, maybe someone else with more Classic experience can help there.

So, hard to say over the internet, but I think that you’ll be OK if you can get a working boot medium - maybe fixing the floppy drive, maybe fixing the HD, or replacing one or both of them.

 

[cheesestraws]

I also can’t boot from the ROM using Cmd + Option + x + o.

Cmd-Opt-X-O only works on the Classic I, not the Classic II. Don't panic about this .

 

[surfer150]

@mdeverhart I don’t hear any ticking from the hard drive. It just spins up and after 10 seconds it spins down again. The hard drive worked perfectly before the recap. I can try with the hard drive from my Performa 475, but it’s a 4 GB one. Does the Classic II accept such large drives?

I will remove the capacitors entirely and test it again. Can someone post me the correct capacitor values of the MP-F75W-01G and make pictures for me to double check if everything is correct? I normally don’t make such mistakes but I should avoid to do solder work at night in the future…

@cheesestraws Why the logic board has socketed ROM chips on it then?

 

[cheesestraws]

@cheesestraws Why the logic board has socketed ROM chips on it then?

What do you mean? I don't see how that follows. The ROMs are socketed on many macs, and most can't ROM boot...

 

[surfer150]

Why they place ROMs on it when you can’t boot from them?

 

[cheesestraws]

Why they place ROMs on it when you can’t boot from them?

The ROMs contain core library routines, core drivers and the software necessary to boot the machine, not a fully copy of the OS, except on the Classic I.

 

[Daniël]

Why they place ROMs on it when you can’t boot from them?

It's similar to a PC BIOS.
There's a ROM containing the BIOS on PC motherboards, but it generally doesn't contain an operating system like DOS, Windows or Linux (disregarding all wacky PCs with built-in mini Linux OSes and such).

 

[surfer150]

@cheesestraws @Daniël Thank you!

 

[surfer150]

I cleaned the PCB of the floppy drive with isopropyl alcohol and cut the legs of the new capacitors a little bit more and now it turns on with the floppy drive connected. Hopefully it now boots from hard drive too.

But can still someone share me the capacitor values of the floppy drive? I just want to get sure I soldered the right ones because I stupid haven’t made any photos before

 

[surfer150]

Still no boot from HDD

But at least it boots from floppy, so the floppy drive is not damaged

 

[surfer150]

During the swapping process with another HDD I saw some leakage from the capacitors in the power supply area of the 40 MB HDD. I will replace them and clean the PCB. Maybe this will solve the issue.

 

[dougg3]

Ahh yes, those are probably good to replace (they look so much like tantalums but they're not). It's still very possible that the sticky rubber is getting you. Maybe the first time you ran it successfully, the head mechanism wasn't fully stuck but after it shut down, it really dug into the sticky rubber and now it can't get out.

Here are a couple of very brief videos I made of a Quantum drive affected by the sticky rubber. It doesn't make any clicking or anything, the head just doesn't move and it decides to spin down almost immediately. It sounds a lot like what you're describing.

And then if I manually (and very carefully) move it just after the drive spins up, it unsticks it from the rubber and all is good (until the next time it is powered off).

 

[surfer150]

I replaced the leaky capacitors and cleaned the PCB. After that I opened the HDD and the rubber was indeed very sticky. I cleaned the entire metal holder properly (it was a mess to handle this goo) and replaced the rubber with a new one but the behavior is still unchanged

Old sticky rubber:


New rubber:


I put in the 4 GB IBM DCAS-34330 from my Performa 475 and it seems to work. It tries to boot but throws an error message (which is normal because Mac OS 8.1 is not compatible with the Classic II)

So it seems that the Quantum is a case for the recycle bin. But it’s not dramatic because I wanted to opt for a larger hard drive anyway.

But I’m glad that it isn’t the SCSI controller or something power supply related.




With disk tools floppy booted

 

[dougg3]

I replaced the leaky capacitors and cleaned the PCB. After that I opened the HDD and the rubber was indeed very sticky. I cleaned the entire metal holder properly (it was a mess to handle this goo) and replaced the rubber with a new one but the behavior is still unchanged

That's really cool that you went in there and replaced the rubber! For what it's worth, that piece of rubber isn't the one that causes the head to get stuck toward the inside. That's the one that prevents the head from coming off the platter.

Based on your pictures I'm guessing this is a Quantum drive that has the second rubber bumper underneath the platter. That's the one that causes the head to stick at startup.

But yeah...if you're planning on replacing it anyway, it's probably not worth the effort of trying to fix it further.

 

[surfer150]

It’s a Quantum ProDrive ELS. As it’s impossible to remove the platter I won’t attempt any further repair and look for a larger replacement drive.

 

[Callan]

You could always opt for a modern replacement like a Zuluscis or Bluescsi. There are no rubber bumpers to worry about. It doesn't have the same ambiance of a spinning drive, but they work great.

 

[surfer150]

BlueSCSI is a cool thing but very expensive when shipped to Germany (about $80) and it’s not the same ambiance as it is with a rattling hard drive. But maybe it is worth the $80 as it enables you to mount floppy images using a web interface which is very convenient.

 

[finkmac]

there's other zulu-class scsi emulators available. some even in the EU