A friend of mine recently asked for my opinion and suggestions on a purchase he was considering. In an e-mail message, he said:

What do you think of this?
(et cetera...)

Even if the memory and power supply are bad I still think the price isn’t bad. I’d appreciate your input. Maybe I’ll come over a little early on Friday and we can look on Ebay for Power Macs. I really want to get one.

I was flattered that he would want my advice, so I decided I would give it the full measure of my attention.
I looked at the item for sale:

Current bid: US $163.50
Apple Powermac G4 Dual 500Mhz for parts

The reason i sell it for parts becaused this Unit can not power up, even though the power button was on and turned off right after that, but the LED light right next to the memory slots was on, so I am not sure the system board is bad or else.

Dual 500Mhz G4 speed processor
80Gg Seagate Hard drive, Power supply
ATI Rage with ADC and DVI connectors
DVD-RAM drive
2 firewire, 2 usb, modem and ethernet

This Unit is sold as describled. So bid with your own risk, I can not warranty any working condition

After seeing this I realized that my friend, who has just recently drank the Apple kool-aid and seen the light regarding Macintosh and OSX, believed he would be able to take this machine apart, replace the broken commodity hadware within it, and end up with a fully-functional machine for a bargain basement price. While this might be possible, I recognized a common misperception which he held. After I shared my opinion with him, I realized this might be useful to others... so I am contributing it here, as a letter to you, my anonymous friends. Consider it helpful advice for those of you who may be looking at a similar purchase.

I told my friend:

I want you to have a Power Mac, too-- but I don't know if I would be very confident about the possibility of resurrecting this system. The seller is talking about how it won't boot, even though parts of the logic board are showing power. This is bad, bad, bad.

Speaking as a former Apple store tech support employee, when we would see a machine behaving like this one, it would almost NEVER be an open-and-shut case of replace the power supply and/or RAM. Usually it was a call to Apple Service for a new logic board. And, if the customer was not bringing in the machine under warranty, they were just as well to start shopping for a new computer and have us cannibalize their old machine for the leftover parts, because the logic board is (unlike a PC) usually the most expensive part of the machine.

I know a lot of your computer hardware experience has been with PC systems-- so it's important to tell you that Mac systems and their power supplies are much more intimately tied together than the typical Windows/Linux box. Each Apple system has its own unique, proprietary power supply which is tied into the logic board in ways which allow it to do all sorts of clever things in terms of system sleep, CPU throttling, waking up on schedule or for network events, automatic restart in power failures, etc... All controlled through the system software, not a separate BIOS menu.

So, just because it's not powering up doesn't mean it's strictly a power problem. And, because the power supply is unique to that subclass of G4 systems (yes, different G4 models have entirely different power supplies) finding a power supply to replace it may be difficult and definitely expensive.

Of course, I may be wrong. It might be a cheap and simple fix... and it certainly looks like it would make a good parts purchase as long as the price didn't go too much higher. But if it were me shopping for myself... And I wanted to have a working system without learning the hard way about where Apple draws the line between commodity hardware you plug in (USB, PCI, AGP, 1394) and its 25-year legacy of building their own custom systems from scratch, then I would probably keep looking.

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