Finally a Macintosh SE - with troubles!

[Sherry Haibara]

Hello guys!
While still trying to get my two Pluses working, last week I've bought a nice Macintosh SE (the FDHD model) for about 60 euros including shipping (the shipping actually cost more than the computer itself!).
This poor guy was advertised as working, but there are a few problems that weren't mentioned in the auction and that I've yet to find an explanation for.

First and foremost: the Mac regularly bombs when booting. It doesn't matter whether it's booting from the internal hard drive (when it works) or from an external SCSI drive.
The bomb is just a generic "address error"; I got it to display something like "error code: -33" or "error code: -12" once when booting from the internal HD, but I haven't been able to reproduce it.
At first I thought it could have been a bad RAM bank, so I replaced them all with known working ones taken from my IIsi (four 1MB banks) - no luck.
I've also tried disconnecting the internal hard drive and the floppy drive, but that hasn't changed anything.
I should mention that my external HD has System 6.0.8 on it and it was previously used to boot my Plus; I don't know what system is installed on the internal HD.

Booting with extensions off is not an option, since I'm running System 6.

Secondly, the internal HD seems to behave oddly: sometimes it doesn't spin up at all, some other times it spins and shows an happy Mac - only to return to the blinking floppy a few seconds later. Is it dying? 

Thirdly, the floppy drive seems to be stuck too. I still have to confirm this, but there's a floppy inside it and I haven't been able to get it out yet, mostly because I don't have access to a working system.

Finally, the power supply may be weak too: it runs fine when accessing only the HD, but if it tries to access the internal floppy, the screen gets darker and keeps changing its brightness, as if there wasn't enough power to run everything.

Any advice about how to proceed now?

Thanks!

 

[techknight]

The power supply is the likely cause of the grand majority of issues.

 

[CelGen]

Secondly, the internal HD seems to behave oddly: sometimes it doesn't spin up at all, some other times it spins and shows an happy Mac - only to return to the blinking floppy a few seconds later. Is it dying?

The Miniscribe drives used in the SE are prone to stiction which causes the drive to not spin up. A brief happy mac followed by the blinking question mark again is normally an indication that the system software is damaged.

 

[Sherry Haibara]

Hi all,

thanks for the suggestion! I should be able to get my hands on a floppy emu by the end of the week and perform some extra tests with a fresh copy of System 6.0.8 Utilities Disk.

The disk drive seems to spin up correctly most of the times since I properly reseated its molex power connector, but I guess it must have a corrupted filesystem since it's not actually booting. 
 

As for the power supply: tech, would a full recap be enough to bring it back to operation? 
I'm not sure why would a weak power supply produce address errors, though... I've also thought that maybe the external SCSI drive that I'm using right now has some incompatible system extension or is itself damaged, but it used to work just fine the last time I used it.

I'll keep you posted!

 

[techknight]

Because if the 5v falls too low it causes VCC glitches and bus glitches. Too low itll bong bong bong....

 

[Sherry Haibara]

Good news! I've managed to have it booting!

So it actually turns out my external hard drive was on its death bed, I used it for a few minutes with my Power Macintosh 8500 and it just died with horrible noises. It's understandable though, it was a 20 MB CMS drive from the end of the 80s...
I've replaced it with the 4.5GB hard drive that was sitting in my IIsi, which has been organized into three partitions: System 6.0.8, 7.1, 7.5. 
I had to fiddle with it for a while because for some strange reason it wouldn't change its SCSI ID from 0 even when configuring the jumpers; in the end I just left it with SCSI ID 0 and I changed the Miniscribe to have SCSI ID 2. And behold, the SE just booted fine with 6.0.8!

System 6 complained that the Miniscribe was unreadable, so I just initialized it. I tried putting the system folder in it to see if it could boot from there, but subsequent tries to boot from the internal hard drive have resulted into multiple "Illegal instruction" bombs, while nothing wrong happens when booting from the external hard drive. I guess it must be dying, too? 

In the end I just disconnected both the Miniscribe and the floppy drive, which was making very terrible noises as if it was going to explode!
I hope it's still salvageable, but if it's not I'll probably look for another superdrive from an LC or similar devices, provided they are compatible. 
I'm also going to replace the Miniscribe with some other SCSI drive - any particular advice regarding the maximum capacity I shouldn't cross, or power consumption limits? I know System 6 can't read partitions greater than 2GB in size and pre-68040 systems cannot use volumes larger than 4GB, but other than that I don't know if there are other limitations. Ideally I would want to avoid taxing the power supply too much.

Speaking of power supplies, I'll see to have it recapped by Ferrix as soon as I can: it's mostly working now, but I noticed a couple of random hangs earlier and some very strange things happening with portions of text replaced by garbage content. I'm sure it's not bad RAM or corrupted files because they've both been in full usage with my IIsi for a long time and they've never shown any sign of instability, so I'd say it's just as tech said: the 5V rail gets too weak and causes bus glitches, freezes and so on.

I've also noticed that the CRT has some burn in, but overall it's still very acceptable - you can see it when it's powered off if you look carefully, but with the system running is effectively unnoticeable.

 

[Sherry Haibara]

So yesterday I had a couple of hours of free time and I decided I would give this poor boy some attention. 

As of now I've replaced both the internal hard drive and the floppy drive with later models and they're working perfectly fine!
The internal hard drive has been replaced with the 4.5GB drive I was mentioning earlier and it's been working with zero issues, it fits very nicely in the case and I've even been able to connect it to the orange activity led to keep everything as stock as possible. 

The floppy drive instead has been replaced with a later 1.4 MB coming from a Power Macintosh and it seems to be humming along perfectly: it's quiet, it works beautifully, it fits the case just as fine as the original and it's fully supported by the Mac since it's an FDHD model.

There are still a couple of problems that bug me and that I haven't been able to fix yet, and they may very well come down to the power supply aging caps.

The oddest one is related to RAM: I've put 4 1MB, 70ms banks on the logic board, switched the appropriate jumper to 2/4MB support but the OS only sees 2MB out of 4. 
The modules themselves are known to be working, since they've been taken from my IIsi which has used them for a long time with zero issues - I've already tried reseating them, but with no luck. I should mention they are probably some high-density SIMMs, since they sport only 3 chips on them and are very compact: I also have a couple of old goldstar SIMMs which are definitely heavier and with a lot more chips on them, summing up to the same 1MB. Is there some known incompatibility between particular types of 30-pin SIMMs and the Macintosh SE? 

The second one is probably due to some instability in the 5V supply: I've used the Mac for a while to test everything was running fine and I've noticed that after a few minutes it just hangs in various ways. 
The first time it bombed with a somewhat flashing dialog box and I couldn't moved the mouse to click the "reset" button; the second time instead, it just froze in the middle of nothing. 
Otherwise the system is running fine and I've already ruled out the hard drive and the RAM, since they're both known to be ok. The logic board seems fine too, no leakage whatsoever.
I'll probably buy a replacement battery for my voltmeter so that I can do some proper measurements from the floppy port and see what's going on.

Meanwhile, I've now got two floppy drives that don't work anymore.
Both of them were completely full of dust in a way that I couldn't have imagined, so I carefully cleaned it with a small brush avoiding to get in contact with the head of the drive.
The first drive just makes a horrible noise (with no disk inserted) which seems to come from the head motor: the head itself doesn't move though and the motor worm doesn't seem to spin. There's also something that prevents the disk from being inserted after a certain point and I'm not really sure what that might be.
The second drive used to work just fine before cleaning (sigh), but now when I insert the floppy it just stays there - the drive motor doesn't spin and it doesn't even attempt to read the floppy, instead it just ejects the media after a couple of seconds. 
I'm no expert when it comes to repairing floppy drives so I'll probably leave this up to ferrix too, but I'm just curious about what might be going on here. Any thoughts?