[BTP]

On a friends old Mac, Power Computing Power Center (= Power Mac 7200) on start up I get a 'bus error' (nothing more than that). I get to the Mac OS screen, but get the bus error just before the extentions would load.

There is noting attached to it except the monitor and keyboard. It will not boot with a boot CD. Nothing has changed at all recently, the computer is untouched and has not been upgraded in a 1-2 years.

I do get a startup chime, I have zapped the PRAM, started with extentions off and still the same thing. The only thing that lead up to this was one oddity. The Apple menu was gone. The first entry was there (About this Macintosh) and nothing else. After a restart, all he got was the 'bus error'. I have no clue what to do here.

Any ideas? It is(was) running OS 9, 384MB RAM w/Voodoo3. I haven't pulled any RAM, but I don't think that is it, unless RAM can just fail and can cause a bus error.

Anyone have any ideas? I am stupmed. It seems that all is well until just before the extentions load and the bus error hits. Since it is the same from the HD or CD, I think it must be hardware, but I'll try anything.

[Rainy Day]

The startup chime, is it the normal chime sound, or something different? Macs run a self-test at power up and if an error is found, they play a different chime sound than normal. If this is true of the Power Computing hardware, however, i have no idea.

What do you mean you can't boot off CD? Does it spin the drive at all? If not, my guess would be that it isn't getting far enough along in the boot process to see the drive. You do know that a lot of the computer is working however: power supply, video circuitry, CPU, ROM, etc.

Most likely cause of this problem: RAM. Can RAM cause a bus error? You bet. In fact, that's about the only thing which can... either because the RAM is physically bad, or because it contains garbage (put there by misbehaving software, or because you've installed a MicroSoft product ).

RAM is the likely culprit, and most probably the lower banks (from the description). Try pulling/swapping RAM until you isolate the offending module.

Note: You may have RAM soldered onto the logic board. Hope that's not what's failed cause you might be SOL. Then again, your friend has probably been wanting an excuse to buy a new iMac! That could just be it.

[Cipher13]

I concur... pull as much RAM as you can while sitll being able to boot OS9 (64 for OS9 required, unless VM is on).

Then, through trial and error, find the bad stick(s).

I think it's the RAM, although the Apple menu thing is wierd; that was probably due to the Finder crashing. I'd lay money on that.

...which may have, in turn, been caused by bad RAM.



Check the RAM.

[BTP]

OK.. Pulling the RAM is worth trying. I'll work with him tomorrow on doing that. That seems like it would make sense.

What I meant about not being able to boot from the CD was just that when I diagnose a problem, booting from the CD-ROM narrows down the problem, usually.

He does want a new Mac, but with a baby on the way, it's not in the cards.

[Cipher13]

Originally posted by BTP:
<STRONG>OK.. Pulling the RAM is worth trying. I'll work with him tomorrow on doing that. That seems like it would make sense.

What I meant about not being able to boot from the CD was just that when I diagnose a problem, booting from the CD-ROM narrows down the problem, usually.

He does want a new Mac, but with a baby on the way, it's not in the cards. </STRONG>

Hmm. When it doesn't boot off the CD, that generally just opens more options, unfortunately.

A mobo component (SCSI controller in this case) could be damaged; or the system can't get far enough into the boot process (VERY unlikely). But, it also means it MIGHT not be the system.

The fact that even a CD won't boot leads me to believe that one or more RAM chips are bad; if not a whole bunch of them, then likely the ones which the system addresses first. Try reversing the order of the first few, and the last few, also.

[BTP]

Well, it doesn't look like its RAM. Every combination was tried, still nothing.

There is just a ATI card on the PCI bus, 2 hard drives, a CD-ROM and a CD-R. Could any of the devices be causing this? Still out of ideas..

The bright side is that he is leaning toward a new Mac, despite what I said earlier.

As far as I know; the 7200 can't be upgraded beyond system 8.1
But then again they say you can't upgrade a non-G3/G4 to OS X.
Good luck.

Zap the PRAM.

That is, Zap the PRAM with the CD in the machine and then hold the c key down and try to boot off the CD. Bus error is almost always an extension conflict. select the startup disk and basic extension set. Trash the Finder, Mac OS and Appearance, if applicable prefs. Make sure you are not trying to load the control strip either.