Power Mac G3 B&W won't boot

Might be time to replace the PRAM Battery, 4 years is close to their lifespan, far less if ever without AC power, & can cause strange startup problems...

http://eshop.macsales.com/item/Newer%20Technology/BAA36VPRAM/

With no AC power a few months will drain the battery.

I agree regarding replacement of the battery. If you have a voltmeter, check it. If you plan to put the computer in storage for a while, it's better to remove the battery because it will drain down sooner than later. It's interesting that the same battery - the 3.6-volt ½AA lithium - is used in wireless alarm system components. A single battery powers the circuit board in each wireless door/window sensor that communicates with the main panel. The main board monitors their output and will warn when a low battery condition exists. In normal use, I've gotten about 10 years of service life from each of them. Leaving one in a disconnected-from-electricity Mac will usually result in a very weak or dead battery in a couple of years. In older Power Macs that ran pre-OS X versions, I used TechTool to save the PRAM prior to removing the battery. After reinstalling the battery and powering up the computer, I'd restore the PRAM from the saved file. That way, the total number of hours of use that the computer had was kept accurately.

You can try resetting the motherboard by disconnecting the keyboard/mouse and power cable. Open the side panel, disconnect the power supply's wiring harness connector, remove the battery, and press the micro "Power Button" on the motherboard (S5 - the one to the right of the CUDA micro-button) for a few seconds. Leave the computer that way for at least 10-15 minutes, then reconnect the power supply and reinstall the battery. Close it up and try starting it again.

The 'hard reset' you suggest, to disconnect the logic board from power supply

was among several items I used when troubleshooting my B&W G3 while in

the process of performing a repair and upgrade. Of course both ends of the

power were disconnected.

With mine, one of the problems was a few extra loose screws left under the

logic board, these moved each time the access door was opened and they

randomly shorted the logic board to the static metal shield on the door. At

least they did not damage the board; I found them after all other troubleshoot

ideas had not resolved a very bizarre set of symptoms. I was going to get to

the bottom of it; & found that in regard to logic, it really did have loose screws.

Courtesy of a previous owner. Curiously, the unit was not missing any.

To have and keep spare 1/2AA 3.6V Lithium batteries (new) on hand is always

a good idea if you happen to own at least one of these computers; + test them.

Had not used the TechTool 'save PRAM' option for a long time. Finally sold the

PM B&W G3 fully optioned with extras, printer, camera; a few years ago and

included several original Apple system discs worth more now than a B&W.

Thanks for sharing! 🙂

The B&W G3 needs the +5 volt trickle power to start up. If you have a voltmeter, you can test the power supply to determine if the trickle power is present. The Apple P-S has a standard 20-pin ATX connector, so pin identifications #s can be found online. With the computer connected to A/C power, but not turned ON, connect the voltmeter's negative probe to pin 16 on the P-S connector, and the positive probe to pin 9. The meter should read +5 volts. If not, the P-S should be replaced. I installed a 300-Watt ATX PSU in one of my B&W G3s, when it did nothing after the power button was pressed. Because the B&W G3 can use a slightly-modified ATX power supply, the replacement isn't difficult. You need an ATX P-S that has its internal cooling fan (or fans) positioned at the back end (or back & front), but not one with a larger cooling fan on its underside. This is due to the vertical orientation of the P-S in a B&W — the power connection cut-out on the blue plastic bezel on the back is below the slotted opening for the P-S's cooling fan. If you installed an ATX P-S with a bottom-mounted fan in a B&W G3, the fan would be facing the chassis wall, and not the motherboard. Obviously, that's a no-go. This page shows the modification that you'll need to perform. You need to cut the P-S lead going to pin 18 (-5 volts) and tape it off. If you don't make the modification to an ATX extension cable, cut the wire at pin 18 about 4 to 5 inches up from the ATX connector. This will provide enough length to splice the lead back together, if desired at a later time. Because you need a ground at pin 18 in the B&W, take the end of the cut wire attached to the ATX plug and fold it back alongside a ground wire in the wiring harness. You can use one of those plastic 3M thru-splice blocks for low voltage wires. Place the insulated wires in the slotted metal contact and then close the plastic cover, snapping it locked (pliers may help). Because an ATX P-S doesn't have the smaller-gauge, twin-lead to power the case cooling fan (as found on the Apple P-S), you'll need to make an adapter by removing/transferring that long, braided twin lead from the P-S and then splice it to a molex power connector. Verify the case fan's power requirement (printed on the label: 5 or 12 volts), and connect it accordingly to the corresponding leads on the molex power plug.

This page is still a good reference for B&W G3 owners.

You may see if a hard-reset of the computer could help. Been quite some time

since I've done that with tower Power Mac computers, including those pre-G3.

Testing, checking, and cleaning connectors to/from the logic board and power

supply can be a fair idea; to leave the connector from the power supply to the

logic board unplugged and the power supply to grid, unplugged, and press the

power button on the computer, (not sure of the order, at this late date) will

de-energize the components. I'd leave them setting awhile, too.

Re-attach them in a chain, starting with the furthest from power supply and

of course, lastly connect the power supply after peripheral mouse/keyboard

and then plug in last to the grid. Delay startup for awhile so it's energized.

There could be a problem with the graphics card, some models of B&W had

an additional card for options or upgrade displays. Mine had most of those

options and upgrades, then sold it to a friend of a friend for good price after

troubleshooting all the issues that about drove me near crazy. I spent hours.

Over a few days. And took the computer down to the bare walls. And fixed it.

Anyway, the need to located known-good used or new old stock components

to have on hand is advised; hard to get as they likely are now. To swap them

and check for a cure that way; which is part of a regular troubleshooting repair

in the official service manual, at some point just before you take a new hobby.

Good luck & happy computing! 🙂