How do I troubleshoot an Apple //e with no power light?

Question

Recently, an Apple //e has come in my possession, and I'm trying to get it to power up. I am looking for some troubleshooting advice. I've looked around online, but there seems to be very little on this sort of repair.

As of right now, I'm just trying to get the power light to light up when I turn on the computer. So far, this is what I've tested:

Cords - I have confirmed that this isn't a problem with a power cord or something like that because when I plug it in and turn it on, I can hear the power supply softly humming.

Power Supply - I tested the voltage of the power supply with a voltmeter by disconnecting it from the motherboard and checking the output of each pin. I compared the values I measured with the ones I found here and confirmed that they are close to the expected levels. I also read somewhere that the power supply is designed to shut itself off if it is not giving the correct outputs. So, it seems to me like this isn't the problem.

Replacing Chips - After testing the power supply, I found an old repair guide that suggested I replace some of the components on the motherboard. In the guide, under start-up problems, it suggested that I replace the following chips if there is no power light: 74LS125, 74S109, and 74S02. However, after replacing all three I found that I still get no power light.

Power LED - I've tested the power LED on the motherboard, and measured only 0.64 V across it with the power on. Furthermore, I don't hear a beep when the system is powered on, and I don't get a signal from the monitor (which works with other sources).

This computer also has multiple cards in the expansion slots (such as a modem controller and RAM expansion). Maybe one of these is faulty? What would be the bare necessities for a system boot?

If there is anything else I can test that would cause such a fatal error as the power light not turning on, please let me know.

Answer 1

Some of your general questions can be answered here.

As I said above, for an Apple //e remove all cards for troubleshooting - none are necessary for boot-up in a typical system. (As opposed to an Apple II or II+ where if there's a card in slot 0 it's likely a "Language Card" with RAM and/or ROM, so that should initially be left in, then perhaps be removed as part of troubleshooting.)

Replacing specific components is warranted only for specific problems, but is unlikely to fix "no power light". If you replace chips at random these new chips might get damaged or (if you're unlucky) even introduce a new problem.

No light means no power, and so nothing else on the board will work, hence no beep etc. The power supply should normally be tested under load (usually a motherboard, but otherwise something you don't care about if the supply is suspect). One likely fault on the motherboard is a short, causing the power supply to shut down. You can start by checking capacitors (usually you'll have to desolder one to confirm the short) especially those next to the power connector, but the short could be anywhere on the board.

So this ends up being a more general question of how to find a short on a PCB. Techniques range from checking temperature (a shorted chip might be hot) to using a multi-meter. You could try removing all socketed chips and see if the light comes on - then it would be a matter of substitution or replacement - but the //e has fewer socketed chips than its simpler predecessors.

FYI there's another repair book, though it's unlikely to help: Sams ComputerFacts - Apple IIe.

Your problem is probably best discussed in a forum with others experienced in hardware troubleshooting and repair, such as the Facebook group Apple II Enthusiasts or the Usenet group comp.sys.apple2.