Macintosh question (G3, 7 years old, so OT) - test-drb@ccmp.vtda.org

28 Jun 2006

...
 Date: Wed, 28 Jun 2006 08:26:41 +0000
From: "Ethan Dicks" <ethan.dicks at gmail.com> 
...
 Does anyone here know about the internals of the G3
line?  I have a
motherboard in front of me that I'm attempting to see if it will work.
  It came from a machine that had already been stripped, so there's no
guarantee the hardware is functional.  With the Apple Reset/NMI board
installed, and RAM, and the Apple-enhanced ATI Rage 128 video card,
I've attempted to see if it works by plugging in a PC ATX power supply
and pressing the "power on" button on the motherboard and on the
Reset/NMI board.  I get a brief green flash from several LEDs, but the
PSU doesn't kick on the fan, and the machine does not appear to be
starting.

Do I need an Apple ATX supply to test this?  Could this be a battery
problem? (the battery was completely dead and I have no handy
replacement, so the battery compartment is empty)
Do I need to have a keyboard and mouse plugged in to get a response? 
The Beige G3 (if you're looking at a Blue & White (Smurf) MB (the 
case was B&W, not the MB), then the following advice is inapplicable) 
motherboard can be used with either a standard ATX power supply or a 
special Apple power supply used in their Desktop version of the case 
(as opposed to Mini-Tower which used ATX).   There is a jumper near 
the rear left corner of the motherboard with which to select the 
power supply being used.

The jumper is probably set improperly, because this machine and the 
similar ones going back before 1996 (On-topic, <grin>) will power up 
even if there's no CPU on the motherboard.   That is, pressing the 
power on button or the power button on the ADB keyboard will still 
power up the supply, even though the motherboard is brain dead.

A Beige G3 could be missing any of three essential components if it 
was stripped.  It needs a CPU, which comes on a 19X19 pin ZIF module. 
I doubt you overlooked that.   It requires a voltage regulator. 
This voltage regulator delivers different voltages to the CPU module 
depending on the setting of sense pins in the 19X19 grid.   This is 
less obvious, but I bet you have that.   If not, it mounts in the ~2" 
vertical slot to the left of the ZIF socket.

Finally, the ROM (firmware) in the Beige G3 is on a DIMM module. 
There were three common revisions of the ROM.  Revision A lacks 
support for slave devices on the EIDE channels.  So only one drive 
per EIDE channel.  Revision B and C are essentially indistinguishable 
except that revision C doesn't play nice with some Skyline ethernet 
devices.   Without a ROM module you won't be able to boot either, 
though it should power up.  The two 32 bit wide ROM chips (weird ROM 
chips, noone makes 32 bit wide nonvolatile storage any more) on the 
Revision A have part numbers ending in 40x.   IIRC they're something 
like 343S040x or some such, but I'm really hazy about the fifth 
character.   The rev. C ROM chips' part numbers end in 49x.   I'm not 
sure about the Rev. B; presumably something between 40x and 49x.  :-)

The battery, keyboard and mouse can all be dispensed with if all you 
wish to do is boot the machine.  The battery is a 1/2AA available at 
Frys for about $6 or at Radio Shack for closer to $12.

Jeff Walther