Completely non-powering up Apple II, where to start?

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Joined: Jan 27 2011
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I have an Apple II Plus that does absolutely nothing when the power switch is flipped. However, the power supply itself is good, as I was able to hook it up to another motherboard and it powered it just fine.

But from the problematic II Plus I get no beep, no video, not even the power indicator light on the keyboard comes on...completely dead.

I've tried fiddling with the connector between the power supply and motherboard to no effect, and have tried reseating the ICs to no avail.

Short of doing an IC-by-IC swap from my known good board, can someone suggest which components to look at first given the completely dead symptoms?

Much thanks,
Howie

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gsmcten's picture
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Joined: Oct 4 2005
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Re: Completely non-powering up Apple II, where to start?

Epoxy,

Have you tried removing any cards and then trying to start up?

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Re: Completely non-powering up Apple II, where to start?

Yes, I've tried it with all cards removed and still nothing.

I should point out, though, that when it's switched on and I fiddle with the video out jack I can see very faint, fleeting flickering lines on my monitor that don't appear when I do the same with the Apple switched off, so it's some sign I guess that power is getting to the board in some capacity. But for all intents and purposes it's just some noise, no semblance of a real video output signal.

Which ICs would fail and cause no video, no beep, and no power indicator light? I'm assuming one of the chips having to do with the power, so which should I swap first?

I'm also assuming that if the 6502 were fried, or one of the ROMs were bad, I'd at least get the keyboard power light to come on, and maybe some garbled (but stable) image on the screen, right?

Any advice would be welcomed, otherwise I'll proceed with a chip-for-chip swap approach from my good board.

Thanks,
Howie

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Joined: Jun 5 2008
Posts: 380
Re: Completely non-powering up Apple II, where to start?

First start with the video section. Start at the output and work back toward the DRAM. Once you get a video signal, you may or may not find that you have a working processor section. If you don't have a working processor section, start at the 6502 and work out across the bus drivers toward the DRAM. It is best to check signals integrity with an oscilloscope rather than blindly swap out chips.

Regards,
Mike Willegal

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Joined: Dec 20 2003
Posts: 359
Re: Completely non-powering up Apple II, where to start?

Had that same situation with a II+ I picked up a year and a half ago.
Unless the bulb is burnt out the keyboard bulb should light up if the power supply is working. It doesn't depend on anything else to function. If it's good then there's no power getting to part or all of the machine.

Here's a copy of the posting I made on my dead II+

Picked up two II+s in the last month. First was a perfectly working RFI II+ in the original box. The second was a Revision 7 I got from a former member of our User Group. It was the most interesting II+ I've received. No beep, no drive activity, no keyboard light, nothing on the screen.
First thought was a dead power supply but checked that out and the power supply was fine.
Checked out the keyboard light and found a burned out bulb. Replaced that and now I have a non functional II+ with a keyboard light.
Next thought was that likely there's no clock signal. Changed the relevant chips with no luck. Finally pulled the board and replaced the crystal. Now I'm making progress. No beep, no drive but now I have garbage on screen.
I try a ROM card to see if I have bad ROMs but no luck. Next I replaced the 6502 and I have a beep and the drive whirs.
Happiness

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Joined: Jan 27 2011
Posts: 110
Re: Completely non-powering up Apple II, where to start?

Thanks Mike and Wayne for your tips. Sounds like first thing to do is swap in my known good motherboard into the case and see if the keyboard power light comes on to verify that the bulb is good. That will tell me if there are power issues with the problem board (and let me assess the functionality of the keyboard itself while I'm at it). From there I can decide whether to swap over the 6502 and ROMs, or swap over ICs related to power and/or video sections to try reviving the problem board.

One concern I'd have is *if* there is a short on the problem board that has damaged the CPU or ROMs, what are the chances that good ICs that I swap in will get zapped immediately? I understand Mike's philosophy of targeted troubleshooting using a scope, but I don't have access to one so IC swapping (although arbitrary) is the best diagnostic method I have to work with.

So given that, it's likely I'll be hitting you guys up for more tips as I make progress.

I really appreciate the help.

Howie

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Joined: Dec 20 2003
Posts: 267
Re: Completely non-powering up Apple II, where to start?

If you are going to remove the motherboard anyway,
get a GOOD magnifier and carefully and patiently
check all of the circuitboard paths (especially
in te area of the power connector) for breaks.

Always helps to check the cheap and obvious first.
Many times that is the culprit.

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