G4 Tower: Doesn't power up!

Yes, those internal batteries, if depleted, can stop a G4 from starting up. 4 or 5 years is about their lifespan.
I would check it first. When mine went, I had no response from my Mac at all; just a light on my power button; absolutely no boot at all.
Check out things in Texas Mac Man's tutorial on the subject. His tutorial is a little dated (don't believe it even mentions G5's) but the info in it, except SMU not being included, still applies.

Cheers!
DALE

The only other thing I noticed is that there is a small silver, braided wire with a funny 'nipple' connector on the end (in brass I think) which looks like it is disconnected from a point near the power button, but then again it could be just meant to be disconnected (ie ready for secondary media like DVD which this Mac doesn't have etc). I couldnt' see anywhere this could be connected.

That's the antenna for the optional Airport card. There should be a plastic clip to hold it out of the way.

Hi, Steve -

Re removing the power supply, you can view/download a how-to PDF and/or a movieclip from links in the appropriate DIY article for your model G4, which you can select from the pulldown menu on this page - http://www.apple.com/support/diy/

Note - if your machine is a G4 (AGP) model, select the one for G4 (Gigabit Ethernet).

Hi, Steve -

What is the model designation for your G4?
Article #58418 - Power Mac G4: How to Differentiate Between Models

Hi, Steve -

This Apple KBase article has a bit more info about testing the power supply in a G4 (Gigabit Ethernet) model -
http://docs.info.apple.com/article.html?artnum=95064

I've never removed nor disconnected one, so can't give advice on what to wiggle, shove, or pull in order to get the connector loose. I do recall on connectors on other devices that in some instances a latching lever-like thing on the side of the connector had to be pried outward, which then allowed the connector to be worked off of the socket.

Perhaps someone else who's done that before will respond with hands-on advice.

Hi Steve!

I just bumped into your thread and I'm hoping that for now, at least, you still haven't managed todisconnect your PSU harness at the logic board. Unless you're bench testing the PSU with a resistance connected to the wiring, it's bad practice to energize it with the harness disconnected. Doing so can burn out the PSU in a very short amount of time.

Test the PSU using the link that Don kindly provided, but do so with the PSU installed and connected to the logic board. Insert the voltmeter probes into the wire side of the connector at the logic board, inserting them into the appropriate wire sockets right alongside the wires. Toward the end of each wire is a metal pin connector which you'll want to insure to make contact with. (Please note that after each test in the linked testing procedure, Apple advises to retest if you don't get a reading the first time. I take this as a double check to insure that probe to pin contact was made.)

I'd start by using the voltmeter set to AC voltage and first test for normal line voltage at the wall receptacle. If normal, connect your power cord to it and test for line voltage at the female end of the cord. If normal, connect the power cord into the Mac, switch the meter to DC voltage, open the side door, and insert the positive (red) probe into pin socket #22, which should be the white wire at the end of the connector for your Mac model. Insert the negative (black) probe alongside pin socket #11, which should be the black wire at the same end of the connector, just across from #22. This should produce a reading of +28 volts, which is the required trickle charge output for an energized power supply on a Gigabit Ethernet or Digital Audio Mac. If the reading is zero, retest to insure your probes indeed made good contact. If your probes are thick or you're unsure that you made metal to metal contact, you might use two straightened paper clips (much thinner) to insert alongside the wires, being careful not to touch them to each other or to touch both of them at the same time with a single probe, creating a short circuit. Then probe the protruding paper clips. If the reading is then still zero, the PSU is defective.

Regarding removing the connector... There's a plastic protrusion at the middle of the backside of the connector which you must press in near the top of the connector to release it from where it latches on a mating part just above the logic board. The harness connector should then pull straight up and off. If it's stubbornly stuck, then I'd first completely de-energize the Mac by unplugging the power cable, removing the internal battery, depressing the front power button for a few seconds, and then allowing the tower to sit for thirty minutes or so to insure that the logic board capacitors are discharged. Then try using a pair of pliers to grasp and carefully pull upward on the connector while depressing the top of the latch I spoke about. That should help you free it. If it still won't loosen, you might try spraying an aerosol dielectric electronics cleaner into the connector, wait a minute or so, then try the pliers again. If, instead, the problem is that the latch doesn't release at the bottom, try inserting a small tool between the connector body and the latch and gently pry the latch outward at the bottom just a tad. It only needs to move less than an eighth of an inch to release it. Then pull the connector straight upward.

Gary

Steve,

I really believe that your power supply was dead from the start.

If you have a blue and white colored G4 with a 22-pin PSU connector, then you need a 338 watt Gigabit Ethernet G4 or Digital Audio G4 power supply, either of which will work in either model. (Here are the Apple Assembly numbers: 614-0112, 614-0120, 614-0137. You might use them to Google for local sources.) The PSU you pull from your Mac should have a label with specs on it, too, if it's still readable.

BTW, you can easily pinpoint which of these models you actually have by counting the number of expansion slots inside. The Gigabit Ethernet Mac has four (1 AGP and 3 PCI slots) and the Digital Audio Mac has five (1 AGP and 4 PCI slots).

Forget about the QuickSilver PSU. It has a 22-pin connector but also has an additional 4-pin connector to the logic board. Additionally, it's trickle charge output is +25 volts (rather than +28v) and it may have a different form factor which may not fit into your tower properly...

Here are two links for the units you can use, which should help you better identify what you're looking for:

http://hardcoremac.stores.yahoo.net/pog4diau66.html

http://hardcoremac.stores.yahoo.net/pog4posu33.html

Note that the type of extra port for a monitor plug, which is furnished on one of the units listed, may be significant, depending on the country for which the PSU was manufactured. (This port is not essential, though.)

Perhaps someone from UK will chime in with a good local source you might use. Rodney Culling probably knows of some.

Gary