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What to do when your Power Mac boots to a “forbidden” symbol

gsteemso

gsteemso

6502
I recently tried to fire up a Mirror Drive Door G4 that hadn’t been powered on in a very long time. Alas, it booted to a blank white screen with a grey circle-with-backslash, a shape familiar to most of us from “No Parking” signs and the like. (Weirdly, the shape was repeated five times across the screen – centred roughly every 400 pixels, more or less.) I tried searching for this phenomenon on the internet, but the only mentions of it I could find didn’t recognize it either.

Luckily for me, I met a man today who _did_ recognize it; he says it probably indicates trouble with the graphics card (which struck me as rather counterintuitive, given that it was able to generate a video signal in the first place).

I’m posting this information here in hopes that it will help someone else who cannot find it.
 
Yeah your graphics card in your MDD is probably dying. Some graphics cards die in such a way where a monitor still recognizes the signal as valid, but it doesn't look right to you and me. I'd try swapping it out if you can
 
That error simply means that the system software is not bootable, generally because the installed system is for different hardware.

Nothing to do with the graphics card.
 
lobust said:
That error simply means that the system software is not bootable, generally because the installed system is for different hardware.

Nothing to do with the graphics card.
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Exactly.. I think it means it found an incompatible (or damaged?) System Folder
 
lobust said:
That error simply means that the system software is not bootable, generally because the installed system is for different hardware.

Nothing to do with the graphics card.
Click to expand...
But the graphics card is probably also going considering it's repeating across the screen
 
Nixontheknight said:
But the graphics card is probably also going considering it's repeating across the screen
Click to expand...

It's certainly possible, but I don't think I would jump to that conclusion if the early boot is failing...

If the video error is present on the OF prompt or the startup manager screen then it would certainly indicate a gpu fault...

cgp said:
What OS is it running? If OSX, boot verbose (cmd-V) to get more clues.
Click to expand...

Idk if verbose or single user would work, I think this screen probably appears earlier in the boot process than that, since any boot error that happens afterwards usually shows a kernel panic instead, right?
 
lobust said:
Idk if verbose or single user would work, I think this screen probably appears earlier in the boot process than that, since any boot error that happens afterwards usually shows a kernel panic instead, right?
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If boot fails earlier, not finding a boot drive, I'd expect the ?-floppy icon. If the booter fails or possibly if the kernel panics early, the circle-slash results. A verbose boot will say more. A safe-boot may be needed if kernel extension caches are corrupt.

If you don't have any luck with that, boot into OFW, have a poke around and type "boot". If the video is shot, you probably won't get any sense with that either.
 
Well, you guys were ALL correct about various things :¬)

I was able to boot into the system picker, which was likewise replicated five times across the width of my display, whereupon the machine revealed itself to have been trying to boot from a (seemingly) nameless volume that, after successfully booting from the actual startup volume, turned out to not contain any system software at all. As best I can tell, this all happened because the PRAM battery had fully discharged, so it was reading nonsense values from PRAM.

Successfully booting did cure the display card of its strange, fivefold horizontal repetition habit.

Long story short, the machine still works! Hooray, cake and streamers, &c.

Thanks, you guys, for all of your suggestions. You saved me a lot of time and effort, and possibly also money.
 
Further oddness… According to Disk Utility, the machine contains five hard drives, of which only three will mount – even though it avers there are no problems whatsoever with either of the other two. Does anyone have any suggestions for how to address that problem? It looks like some of the data I hoped to recover are on one or the other of the unmountable pair.
 
gsteemso said:
Further oddness… According to Disk Utility, the machine contains five hard drives, of which only three will mount – even though it avers there are no problems whatsoever with either of the other two. Does anyone have any suggestions for how to address that problem? It looks like some of the data I hoped to recover are on one or the other of the unmountable pair.
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Get a disk utility listing of all drives from the command line "diskutil list". That'll tell you what the organization is (partitions, volume types and sizes, etc). You may need to run First Aid to fix-up some volumes .. but start with the listing.
 
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gsteemso said:
Well, you guys were ALL correct about various things :¬)

I was able to boot into the system picker, which was likewise replicated five times across the width of my display, whereupon the machine revealed itself to have been trying to boot from a (seemingly) nameless volume that, after successfully booting from the actual startup volume, turned out to not contain any system software at all. As best I can tell, this all happened because the PRAM battery had fully discharged, so it was reading nonsense values from PRAM.

Successfully booting did cure the display card of its strange, fivefold horizontal repetition habit.

Long story short, the machine still works! Hooray, cake and streamers, &c.

Thanks, you guys, for all of your suggestions. You saved me a lot of time and effort, and possibly also money.
Click to expand...

That's good!

I wonder if you have a flashed PC video card of some description in there? Some of those don't work properly in framebuffer mode during boot...
 
Well, I screwed up pretty severely. It turns out there were in fact only four physical drives in the machine; the illusory fifth was a RAID group that only had one member – namely, one of the drives that seemingly wouldn’t mount. In the mistaken belief that there were five physical drives, and believing that the unmountable one had gotten separated from the RAID group somehow, I tried to partition it (using the “current layout”). Naturally, it turned out that this volume was in fact the backing store for the *mounted* RAID group, which promptly evaporated. There was a whole bunch of stuff I wanted on there, up to and including backups from 30 years ago. Now, I didn't use any fancy erasure scheme or anything, so in theory all that stuff is still on the drive, if I can reconstruct the HFS+ volume around it. I unmounted the seemingly-blank drive as soon as I worked out what I’d done, so it’s unlikely to have gotten very corrupted in the interim. What software should I use to attempt recovery? I know it exists, just not what it’s called.

Also, the other unmountable drive turned out to be the Mac OS 9 boot volume. It tested OK with every utility I threw at it, but absolutely would not mount even when it claimed it had. Using `fsck_hfs -dfr` on it revealed that there had in fact been an undetected error in the catalogue file, but it claimed to have repaired it correctly. Still won’t mount, though – it just claims to have. Very odd.
 
Well, I am just batting 1000 today.

After a few minutes’ searching around, I discovered “TestDisk” (https://www.cgsecurity.org/wiki/TestDisk_Download). All set to finally get some answers, I plopped the new PRAM battery that arrived a few minutes ago into the machine, hit the power button, and… nothing. The computer is as dead as a doornail. The battery is of the correct voltage (verified by meter) and inserted the right way around, and removing it again didn’t help. I’ve read elsewhere that these models tend to suffer from abrupt power-supply failures – is there a quick way to test that? I can pull it out of the chassis and put multimeter probes on the leads, but if there’s an easier way I’m all ears.
 
Yep, it was the PMU. What a relief!
Had to zap the PRAM before it would boot afterwards, but all in all, a pretty smooth experience.
 
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