Thread
IIfx Won't boot
being that large its not going to be anything mission critical (big farads = low frequency filter, or a really half hearted fudge of a timer) I have just been cleaning and sorting through stuff preparing to let my wife know about the //c (shh) that I am going to rebuild this summer once we get some good retrObright weather
Nice work Dennis! 
Well I finally got the IIfx working. Turns out both of my SuperDrives are bad (not sure if they're fixable) but I had a spare working HD so I was able to get it to boot into System 6.0.8. I still can't get that SuperMac video card to reset itself for my new monitor, but I found I also have a RasterOps 8XL card which seemed to like my monitor just fine. Unfortunately I only have 8MB of memory as 16 of the memory sticks I have are 1MB sticks and the other 4 appear to be bad (the Mac won't boot with them in), but I assume they're also 1MB sticks.
Tempest
Tempest
If the RAM is bad, the Mac should make a death chime instead of, or in addition to, the normal startup sound.
Bad RAM can be caused by:
- Dirty connectors (clean with an eraser)
- Mismatched RAM, maybe some SIMMs are different sizes than others
- One or more SIMMs is bad
Did you find your hard drive power connector?
Yes I found it.
When I put the 'bad' set of RAM in I get a normal chime but then nothing happens (the OS never loads). When I stick a good set in the other bank I get the chimes of death sound.
Tempest
When I put the 'bad' set of RAM in I get a normal chime but then nothing happens (the OS never loads). When I stick a good set in the other bank I get the chimes of death sound.
Tempest
If these SIMMs are all identical, then at least 1 of the 4 is dirty or bad. Check to see if the numbers on the actual chips match from SIMM to SIMM. If they're different at all, that could be the problem.
8MB actually will still get you a long way with a Mac IIfx. Apps and Mac OS from back then are very conservative with RAM.
8MB actually will still get you a long way with a Mac IIfx. Apps and Mac OS from back then are very conservative with RAM.
just something to try ...scuffing the contacts lightly with some fine grit steel wool, works better than pencil eraser on mismatched "settled in" parts, but its dust is highly conductive
a small stiff brush submerged with the board in a cleaning solution is a sure fire way to be sure, but a fine point pinch of wool carefully applied and some compressed air can be effective with care
a small stiff brush submerged with the board in a cleaning solution is a sure fire way to be sure, but a fine point pinch of wool carefully applied and some compressed air can be effective with care
Ok I'll try the steel wool. I tried a pencil eraser but it didn't seem to help. The contacts on one seem to be a bit corroded or damaged so that's probably the issue.
Tempest
Tempest
Instead of starting a new thread I'll tack onto this one.
I'm trying to get my "new" IIfx working here. Initially it didn't power on. I added in two batteries and that got it to boot, but the hard drive didn't spin up. I tried to boot from a floppy and it started to load, a SuperMac logo appeared and the floppy was ejected.
Now it chimes, the sound seems to initialise but that's as far as it goes. The floppy isn't powering up any more and there's nothing onscreen.
I pulled one of the SuperMac cards to try to ID it. I also connected up the hard disk from my LC III (just the power cable, not the SCSI) to check that the PSU was working OK. The LC III disk spun up fine so the fault seems to be with the IIfx hard disk. I also tried to hook up the LC III's floppy to check if it would boot any further (perhaps the IIfx's one is faulty). It didn't power up. So somewhere along the way, one of these things I tried seems to have messed things up. Has anyone any ideas?
Updates:
I pulled the second SuperMac card and the drives and booted to a grey screen. Put the drives back and I still boot to a grey screen. If I pull the power cable from the hard drive it boots to the grey screen with the SuperMac logo in the bottom right corner. The floppy isn't powering up at all.
Both cards installed and no drives gets me to a grey screen. Attaching the LC III floppy yields the same, but the drive doesn't try to read or boot the inserted floppy. Reconnecting the hard drive's scsi cable (but not power) and the floppy gets me the grey screen with the SuperMac logo, but no movement out of the floppy drive. Reconnecting the hard drive's power cable as well, gets me the grey screen without the SuperMac logo.
If I lift up the floppy disk inside the drive, I can hear heads/motor at work. So it is getting power at least. Could I have damaged the floppy connector on the IIfx logic board in some way by hooking up the floppy from the LC III?
I tried the IIfx floppy on the LC III and it "works" but floppies are unreadable and when it tried to format it failed verification. So I guess it's gonna need a look at.
I'm trying to get my "new" IIfx working here. Initially it didn't power on. I added in two batteries and that got it to boot, but the hard drive didn't spin up. I tried to boot from a floppy and it started to load, a SuperMac logo appeared and the floppy was ejected.
Now it chimes, the sound seems to initialise but that's as far as it goes. The floppy isn't powering up any more and there's nothing onscreen.
I pulled one of the SuperMac cards to try to ID it. I also connected up the hard disk from my LC III (just the power cable, not the SCSI) to check that the PSU was working OK. The LC III disk spun up fine so the fault seems to be with the IIfx hard disk. I also tried to hook up the LC III's floppy to check if it would boot any further (perhaps the IIfx's one is faulty). It didn't power up. So somewhere along the way, one of these things I tried seems to have messed things up. Has anyone any ideas?
Updates:
I pulled the second SuperMac card and the drives and booted to a grey screen. Put the drives back and I still boot to a grey screen. If I pull the power cable from the hard drive it boots to the grey screen with the SuperMac logo in the bottom right corner. The floppy isn't powering up at all.
Both cards installed and no drives gets me to a grey screen. Attaching the LC III floppy yields the same, but the drive doesn't try to read or boot the inserted floppy. Reconnecting the hard drive's scsi cable (but not power) and the floppy gets me the grey screen with the SuperMac logo, but no movement out of the floppy drive. Reconnecting the hard drive's power cable as well, gets me the grey screen without the SuperMac logo.
If I lift up the floppy disk inside the drive, I can hear heads/motor at work. So it is getting power at least. Could I have damaged the floppy connector on the IIfx logic board in some way by hooking up the floppy from the LC III?
I tried the IIfx floppy on the LC III and it "works" but floppies are unreadable and when it tried to format it failed verification. So I guess it's gonna need a look at.
Still no progress. I can't get it to boot beyond these grey screens. I've tried the internal disk from my 7500 and an external SCSI (as apparently you don't need the black terminator for newer drives).
The first time I powered it on after putting in the batteries it got to the "missing system" blinking icon. Never saw it again.
The first time I powered it on after putting in the batteries it got to the "missing system" blinking icon. Never saw it again.
Do you have a voltmeter? I would start by measuring the output of the power supply and determine if the 5V is at 5V and the 12V is at 12V, etc.
I'm not sure the LCIII floppy will work in the IIfx. It shouldn't hurt anything to try, but using a manual inject floppy drive in a machine that expects an auto-inject drive is problematical. I think it requires a different cable, at the least.
Unfortunately no. I'm not really equipped for this level of troubleshooting. I'm still at the swap-with-a-known-good-part stage.
I've stripped it down a bit now. Disconnected everything from the logic board except for the PSU connector as that's very tight. At a minimum, what should I need connected to at least get it to check for a system disk to boot from? ROM, one gfx card and a stick of RAM? What about the internal SCSI bus? The service manual says I need a special terminator if there is no drive attached. I've tried attaching two drives (Apple branded from my 7500 and a non-Apple Quantum from my LC III) and neither got me any further than the dead 160SC it came with.
I only got the flashing "missing system" icon the first time it booted after I added the batteries. I'm thinking I might have damaged something with my hardware swapping, but I can't be sure. I'd just like to see it get that far again for peace of mind. The only way I can do a PRAM reset is to remove the batteries as the keyboard doesn't do anything when sitting on the grey screen.
I used the IIfx floppy cable both when connecting the LC III floppy to the IIfx and the IIfx floppy to the LC III. The LC III's one was just too short.
I've stripped it down a bit now. Disconnected everything from the logic board except for the PSU connector as that's very tight. At a minimum, what should I need connected to at least get it to check for a system disk to boot from? ROM, one gfx card and a stick of RAM? What about the internal SCSI bus? The service manual says I need a special terminator if there is no drive attached. I've tried attaching two drives (Apple branded from my 7500 and a non-Apple Quantum from my LC III) and neither got me any further than the dead 160SC it came with.
I only got the flashing "missing system" icon the first time it booted after I added the batteries. I'm thinking I might have damaged something with my hardware swapping, but I can't be sure. I'd just like to see it get that far again for peace of mind. The only way I can do a PRAM reset is to remove the batteries as the keyboard doesn't do anything when sitting on the grey screen.
I used the IIfx floppy cable both when connecting the LC III floppy to the IIfx and the IIfx floppy to the LC III. The LC III's one was just too short.
A friend called over earlier with a multimeter and the PSU checks out. +12v, -12v and +5v in all the right places. The batteries checked out too.
I just tried the hard disk from my Classic II but it still won't go past the grey screen (no rounded edges btw). So that's power ok and known-good HD not booting it. I've tried the hard disk cable from the Classic II as well, to ensure the problem isn't with the IIfx's cable. I've also tried moving the gfx card to another slot.
Board wash maybe?
I just tried the hard disk from my Classic II but it still won't go past the grey screen (no rounded edges btw). So that's power ok and known-good HD not booting it. I've tried the hard disk cable from the Classic II as well, to ensure the problem isn't with the IIfx's cable. I've also tried moving the gfx card to another slot.
Board wash maybe?
Maybe, but it seems unlikely. Every IIfx I've seen has tantalum caps installed. I'm not sure what could leak onto the board that would need washing off, assuming the batteries have never leaked onto it.
Freezing at a gray screen can be an indication of a SCSI bus problem. Usually a very bad termination problem. So your problem may be as simple as the missing terminator. Both ends of the SCSI bus should be terminated, so even with a good terminated hard drive on the bus, you may still have problems because the IIfx end isn't terminated without the internal terminator. I think. I can't remember if the motherboard provides automatic termination if no devices are connected.
Hmmmm.
1) Have you tried it with no SCSI cable attached at all? This should get you to a flashing question mark.
2) If 1) fails, do you have a second known good SCSI drive and an internal SCSI cable with three or more connectors?
A) Do not connect any external SCSI cables.
B) Plug one of the middle connectors of the internal SCSI cable into the logic board.
C) Make sure that termination is enabled on both of your known good drives. Double check the jumpers.
D) Make sure that "Termination Power" (different from termination) is disabled on both drives.
E) Plug the known good SCSI drives into the connectors at the ends of the internal SCSI cable. One on each end.
F) Try it.
G) If that doesn't work try enabling "Termination Power" on one (only one) of the two drives.
3) If that doesn't work, buy or build the special terminator for the IIfx and try that....
Thanks for the ideas.
I'm pretty sure I tried with no scsi cable attached and got the grey screen. I'll try it again soon and see what happens (I have it sitting with batteries out right now to reset the PRAM). I'll check the SCSI cable in my 7500 and see if that has 3 connectors. Then I could use that, the 7500's hard disk and maybe a scsi cd/dvd drive (otherwise I'll have to open up my Classic II again to get it's hard disk).
I've suspected scsi voodoo as I think I got a similar grey screen when I attached an external CD to my Classic II. It worked fine on the LC III but not on the Classic II until I attached a terminator to the CD enclosure. What's bugging me about the scsi voodoo situation is that the first time I powered it up I got to the flashing disk icon. So the current set-up of drives and cables etc and termination (or lack thereof) worked briefly yesterday. But not any more.
Update:
Booting with no scsi cable attached does indeed give just the grey screen.
7500's SCSI cable has 4 connectors so I'll work on taking that out now.)
7500's hard disk doesn't have any jumpers. Will it be OK to use two optical drives? I'm assuming the purpose is to have a SCSI device on either end. They don't have to be hard disks?
I went ahead and tried with the CDROM and hard disk from the 7500. The hard disk had no jumpers but the same drive/cable setup works without issue on the 7500, so I guess that means both are setup ok for termination. Still a grey screen.
Tried again with 7500 and LC III hard disks. Same outcome. Neither drive has any jumpers.
I'm pretty sure I tried with no scsi cable attached and got the grey screen. I'll try it again soon and see what happens (I have it sitting with batteries out right now to reset the PRAM). I'll check the SCSI cable in my 7500 and see if that has 3 connectors. Then I could use that, the 7500's hard disk and maybe a scsi cd/dvd drive (otherwise I'll have to open up my Classic II again to get it's hard disk).
I've suspected scsi voodoo as I think I got a similar grey screen when I attached an external CD to my Classic II. It worked fine on the LC III but not on the Classic II until I attached a terminator to the CD enclosure. What's bugging me about the scsi voodoo situation is that the first time I powered it up I got to the flashing disk icon. So the current set-up of drives and cables etc and termination (or lack thereof) worked briefly yesterday. But not any more.
Update:
Booting with no scsi cable attached does indeed give just the grey screen.
7500's SCSI cable has 4 connectors so I'll work on taking that out now.)
7500's hard disk doesn't have any jumpers. Will it be OK to use two optical drives? I'm assuming the purpose is to have a SCSI device on either end. They don't have to be hard disks?
I went ahead and tried with the CDROM and hard disk from the 7500. The hard disk had no jumpers but the same drive/cable setup works without issue on the 7500, so I guess that means both are setup ok for termination. Still a grey screen.
Tried again with 7500 and LC III hard disks. Same outcome. Neither drive has any jumpers.
Ran out of edit time on the last post.
Using the 7500's jumper-less hard disk and cdrom I get the grey screen with term power enabled or disabled on the cdrom.
Using the 7500's jumper-less hard disk and cdrom I get the grey screen with term power enabled or disabled on the cdrom.
Okay, they don't have any jumpers, but does that mean that they don't have any jumper pins? I've never seen a SCSI drive without jumper pins (or resistor packs) to set the termination. I think you may need to reexamine those drives.
On hard drives the pins are often on the flat bottom of the drive and may be really really tiny. They are only rarely actually on the end of the drive with the power and interface cable connectors.
Whether you can assume that the 7500 drive was set to terminate depends on whether the drive was at the end of the cable. Sometimes the optical drive is at the end of the cable and provides termination and the hard drive is on an intermediate connector. It also depends on whether the 7500 is still in its stock configuration and hasn't possibly been misconfigured by someone in the past. Remember, the reason why SCSI has voodoo, isn't because it doesn't work when it should, it's because sometimes it works when it shouldn't. So even if you're 7500 was working properly, you can't assume that it was configured properly, unless you're the original owner.
On hard drives the pins are often on the flat bottom of the drive and may be really really tiny. They are only rarely actually on the end of the drive with the power and interface cable connectors.
Whether you can assume that the 7500 drive was set to terminate depends on whether the drive was at the end of the cable. Sometimes the optical drive is at the end of the cable and provides termination and the hard drive is on an intermediate connector. It also depends on whether the 7500 is still in its stock configuration and hasn't possibly been misconfigured by someone in the past. Remember, the reason why SCSI has voodoo, isn't because it doesn't work when it should, it's because sometimes it works when it shouldn't. So even if you're 7500 was working properly, you can't assume that it was configured properly, unless you're the original owner.
On the 7500 the hard disk was on the end of the cable with the cdrom as intermediate.
You're right. I assumed the term jumper would be at the back. I took off the drive sled and there's 7 sets of pins with two jumpers on the pcb. No marking as to which pin is which though.
Google time...
According to the jumper list, enable terminator and disable unit attention are jumpered. So it's terminated alright. I'm only assuming the cdrom is terminating though. As that doesn't have any term jumper. Only one for term power. The jumper beside it isn't marked (or in use).
Looking at the LC III's disk again, termination is enabled there too. I don't see an option on either hard drive for term power though.
You're right. I assumed the term jumper would be at the back. I took off the drive sled and there's 7 sets of pins with two jumpers on the pcb. No marking as to which pin is which though.
Google time...
According to the jumper list, enable terminator and disable unit attention are jumpered. So it's terminated alright. I'm only assuming the cdrom is terminating though. As that doesn't have any term jumper. Only one for term power. The jumper beside it isn't marked (or in use).
Looking at the LC III's disk again, termination is enabled there too. I don't see an option on either hard drive for term power though.
Last test for tonight. I put my 7500 hard disk in the LC III, wiped it and installed a fresh System 7.5 for all Macs (I tried 7.1 but the resulting install wouldn't boot the LC III for some reason). Took out the gfx card from the IIfx and put in the fresh System 7.5 drive. This way, if the drive booted OK, it would single out the gfx card as being the culprit.
Well, it didn't. No booting at all. Most reports I'm seeing online say you can dispense with the special IIfx terminators if the drives have active termination. So with that in mind I'm assuming that this drive should have booted OK. So am I right in saying this leaves me with flaky SCSI? Maybe the fact that it booted the first time was the voodoo kicking in. If that is the case then I'm probably hosed.
Well, it didn't. No booting at all. Most reports I'm seeing online say you can dispense with the special IIfx terminators if the drives have active termination. So with that in mind I'm assuming that this drive should have booted OK. So am I right in saying this leaves me with flaky SCSI? Maybe the fact that it booted the first time was the voodoo kicking in. If that is the case then I'm probably hosed.
I'm still a bit confused by this claim that active terminating drives don't need special termination on the IIfx. The dead IIfx hard disk is the only one that when connected up to the SCSI bus (with no power cable connected) gives me the SuperMac logo on-screen. Why can't the other drives do this?
I connected up the IIfx's floppy to the LC III last night to eject the 6.0.8L disk that was stuck in it. It actually tried to boot it (but stopped because of the system version). So I popped in a 7.5 Network Access Disk and it booted right to the desktop. Yet on the IIfx it doesn't even look for a disk. Could I maybe have bad RAM or a bad slot? It's going to be a little tricky to test as I can't put this RAM into anything else. I'll just have to go through it stick-by-stick and slot-by-slot.
I connected up the IIfx's floppy to the LC III last night to eject the 6.0.8L disk that was stuck in it. It actually tried to boot it (but stopped because of the system version). So I popped in a 7.5 Network Access Disk and it booted right to the desktop. Yet on the IIfx it doesn't even look for a disk. Could I maybe have bad RAM or a bad slot? It's going to be a little tricky to test as I can't put this RAM into anything else. I'll just have to go through it stick-by-stick and slot-by-slot.
I took out the RAM and ROM and cleaned the contacts on them with q-tips and isopropyl alcohol. Still no improvement. The RAM slots are in two banks of four. If I leave two slots empty in one bank I get a death chime. Filling them up again it goes away.
Still flummoxed with this logo. Surely if the drives are not getting any power they shouldn't be terminating at all?
Still flummoxed with this logo. Surely if the drives are not getting any power they shouldn't be terminating at all?
The SuperMac image is resident in the firmware for the video card. That is, it lives on the EEPROM chip on the video card.
If you're not getting that screen with some configurations, then those configurations are probably hanging before it reaches that point in the boot process. It is also possible, I suppose, that the screen flashes by too fast to see it, but that seems far fetched.
RAM must be installed in groups of 4. And if RAM is installed in only one bank, it must be Bank (?). I can't remember. But there are only two of them. So you could try populating one bank only. Then try populating the other bank only.
Try booting with no RAM installed, no floppy connect and no hard drive connected.
There's 32KB of cache on the logic board, and the IIfx can get pretty far in the boot process just by using that 32KB cache. At least, that's what I remember. I can't remember how far, but I remember being surprised by how far along it got.
There are some jumpers on the IIfx logic board which must be configured properly. I've never seen any documentation about what they do. I'll try to remember to note the condition of each jumper (installed, not installed) on my machine at home, but my memory for things after I leave work is not very good. It could take a while.
If you're not getting that screen with some configurations, then those configurations are probably hanging before it reaches that point in the boot process. It is also possible, I suppose, that the screen flashes by too fast to see it, but that seems far fetched.
RAM must be installed in groups of 4. And if RAM is installed in only one bank, it must be Bank (?). I can't remember. But there are only two of them. So you could try populating one bank only. Then try populating the other bank only.
Try booting with no RAM installed, no floppy connect and no hard drive connected.
There's 32KB of cache on the logic board, and the IIfx can get pretty far in the boot process just by using that 32KB cache. At least, that's what I remember. I can't remember how far, but I remember being surprised by how far along it got.
There are some jumpers on the IIfx logic board which must be configured properly. I've never seen any documentation about what they do. I'll try to remember to note the condition of each jumper (installed, not installed) on my machine at home, but my memory for things after I leave work is not very good. It could take a while.
The screen takes a bit of time to kick in, so it's possible that the SuperMac logo appears before the grey screen with the other drives. By the time the screen is visible the logo is either there or it isn't. The one and only time it booted I think it popped up after the Happy Mac. The boot floppy started loading, then the logo appeared and the disk was ejected, leaving me with the missing system icon.
I tried a few different memory setups. It needs at least 4 sticks to boot (the display won't kick in). It won't go anywhere with no RAM installed. I've also tried filling each bank by itself. I think it's Bank A that should be filled first. It's the faster of the two (or something like that). I also tried mixing the 4 sticks between the two banks by filling the first slots in numerical order (they're numbered J30 - J37 but the slots aren't numbered in sequence). I spotted those jumpers but I haven't looked them up to see what they do. I'm assuming for now that they're set correctly.
I've also tried with no hard disk and no floppy. It just keeps hanging on this grey screen. Nothing will convince it to go any further. What could cause it to hang this early on? I don't think it can be the display card because even without it, it still won't boot either the floppy or the hard disk. And I know both of those are good. Would those tests with the hard disks/cdrom and the 7500's cable have ruled out SCSI termination issues?
I think the only thing left I can try for now is to wash the board. Perhaps there's something causing it to flake out. I can't see any apparent leakage but it is a bit dusty so there might be something there. Also I don't know what the underside of the board is like. The base of the chassis has some visible corrosion. My Classic II was slow to boot sometimes and eventually just packed up with the thick vertical stripes. Since washing the board it boots up straight away. I'll need to recap it at some stage but the wash worked well. I guess it can't hurt to try it anyway.
Thanks for the ideas. I'm sure we'll figure out a way to get it running again.
I tried a few different memory setups. It needs at least 4 sticks to boot (the display won't kick in). It won't go anywhere with no RAM installed. I've also tried filling each bank by itself. I think it's Bank A that should be filled first. It's the faster of the two (or something like that). I also tried mixing the 4 sticks between the two banks by filling the first slots in numerical order (they're numbered J30 - J37 but the slots aren't numbered in sequence). I spotted those jumpers but I haven't looked them up to see what they do. I'm assuming for now that they're set correctly.
I've also tried with no hard disk and no floppy. It just keeps hanging on this grey screen. Nothing will convince it to go any further. What could cause it to hang this early on? I don't think it can be the display card because even without it, it still won't boot either the floppy or the hard disk. And I know both of those are good. Would those tests with the hard disks/cdrom and the 7500's cable have ruled out SCSI termination issues?
I think the only thing left I can try for now is to wash the board. Perhaps there's something causing it to flake out. I can't see any apparent leakage but it is a bit dusty so there might be something there. Also I don't know what the underside of the board is like. The base of the chassis has some visible corrosion. My Classic II was slow to boot sometimes and eventually just packed up with the thick vertical stripes. Since washing the board it boots up straight away. I'll need to recap it at some stage but the wash worked well. I guess it can't hurt to try it anyway.
Thanks for the ideas. I'm sure we'll figure out a way to get it running again.
I read back over the start of this thread again. Just wanted to add some pieces of info.
I too have two different brands of RAM. 4x Texas Instruments and 4x Accutek. I've tried each brand in Bank A.
Unlike Tempest's IIfx, the keyboard lights DON'T blink on startup. The only time they light up is when I power-on (which is usually from the keyboard's power key). After that I hear two pops from the speaker and then the display fires up to the grey screen.
As for the jumpers (partially documented here), J106 is open, J103 is closed. This seems to be the correct setup.
I tried it again with no RAM installed. It chimed but the speaker didn't initialise and the keyboard light didn't blink.
I too have two different brands of RAM. 4x Texas Instruments and 4x Accutek. I've tried each brand in Bank A.
Unlike Tempest's IIfx, the keyboard lights DON'T blink on startup. The only time they light up is when I power-on (which is usually from the keyboard's power key). After that I hear two pops from the speaker and then the display fires up to the grey screen.
As for the jumpers (partially documented here), J106 is open, J103 is closed. This seems to be the correct setup.
I tried it again with no RAM installed. It chimed but the speaker didn't initialise and the keyboard light didn't blink.
That is a great find. Nice to know. I tried googling and never found anything myself.
That may be as far as I got. Getting a chime with no RAM installed is unusual, and is probably because the cache is there to use as scratch space for the functions up to the chime.
As to your problem, I'm still inclined to believe SCSI problem, but I would expect you to get to the flashing question mark with no cable plugged in. It's conceivable that it needs the internal terminator even with no cable attached, but again, far fetched.
No, the 7300/Classic drive test doesn't necessarily prove anything, because this IIfx could be finicky and could really need the special terminator. But the 7300/Classic drive test was indicative. It suggests that the problem is not SCSI related, but it could still be.
Can you hear hard drive activity when those drives are booting in your other machines?
You migth try pulling the video card(s) and attach the SCSI drive with a usable operating system on it. Then listen for drive activity beyond the initial spin up and seek. If it sounds like the thing is loading the OS, then the problem is probably the video card hanging up the bus. Even better would be if you have LED activity indicator you can attach to the hard drive. You'd have to identify the pins for it on the drive though. Although, some drives have an LED built-on.
These are the sort of low probability suggestions at this point....
You're somewhat hampered by not having a different working NuBus machine on hand that you could use as a test bed for comparison.
I was away on holidays for a few days so I haven't been back to this yet. I'd tried it with the 7500's drive freshly-formatted with a universal 7.5 install and no gfx card but it just won't booting anything. The drives I tried are good in their host Macs. I should look up how to attach a LED but with SCSI disks you can pretty much hear them in action once the case is open.
I'm still suspecting SCSI voodoo on the internal bus and hope to be able to check this out in the coming days as I have an internal scsi filter/terminator block combo en-route.
Well that didn't work out either.
SCSI filter on the 7500's hard disk didn't change anything. Filter and terminator (and no internal drive) also didn't boot. I added an external hard disk in case it still needed the external bus terminated as well. No change (though I'm only assuming it was new enough to have the required active termination). Pulled all the cards (gfx and network) as well.
I guess the final step is to get my friend up again with his multimeter and check for shorts or whatever.
SCSI filter on the 7500's hard disk didn't change anything. Filter and terminator (and no internal drive) also didn't boot. I added an external hard disk in case it still needed the external bus terminated as well. No change (though I'm only assuming it was new enough to have the required active termination). Pulled all the cards (gfx and network) as well.
I guess the final step is to get my friend up again with his multimeter and check for shorts or whatever.