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Power Macintosh 5500 troubleshooting

nzsabuga

macrumors newbie
Original poster
Jul 13, 2020
4
1
Hi everyone!

Just picked up a wonderfully yellowed Power Macintosh 5500 over the weekend. It's not working, but I'm a but stumped on where the issue is. When plugging in the power cord, you can hear the CRT 'click' like it's just done a degauss. When you turn it on from the power button on the keyboard, all the fans spin up, the hard drive turns on, and it makes the usual chime, but the screen never turns on. The HDD is noisy enough that I can tell that it's not booting. The green power light on the front doesn't light up either (not sure if it's just the LED broken, or if that's a sign of something?
I've re-seated the logic board, and tried removing the TV tuner card, re-seating the RAM etc.
One interesting thing I found is that if I connect it to power with the logic board removed, the screen powers up, and shows a bright white screen, so the CRT seems to be ok. I've checked the logic board, and there doesn't seem to be any capacitor issues (none look to be leaking anyways). I've removed the clock battery (it hadn't leaked). I'm a bit stumped as to what the issue is with it (logic board stuffed, or maybe PSU/analog board?). If anyone has any insights, I'd be very grateful.
 
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DeltaMac

macrumors G4
Jul 30, 2003
10,660
2,883
Delaware
You said you removed the battery. Did you test it? It should be more than 3.0 volts. The connector for that has two contacts on the flat side of the connector. If the battery tests good, leave it unplugged for 5 to 10 minutes, to allow the logic board to reset -- then reconnect the battery, press and release the CUDA reset button (near the RAM slots)

Hopefully, that powermac will start up this time. If there is no change - - I would suspect the analog board.
 
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nzsabuga

macrumors newbie
Original poster
Jul 13, 2020
4
1
You said you removed the battery. Did you test it? It should be more than 3.0 volts. The connector for that has two contacts on the flat side of the connector. If the battery tests good, leave it unplugged for 5 to 10 minutes, to allow the logic board to reset -- then reconnect the battery, press and release the CUDA reset button (near the RAM slots)

Hopefully, that powermac will start up this time. If there is no change - - I would suspect the analog board.
Ah, does it need a good battery to work? I removed it, and didn't re-install it.
 
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DeltaMac

macrumors G4
Jul 30, 2003
10,660
2,883
Delaware
Did you test that battery? Might be good! (but probably not) It should be more than 3 volts.
One thing to keep in mind, it is not just a "clock battery"
It maintains certain hardware settings in the system, mainly the CUDA chip. THAT chip:
Turns system power on or off
Manages system resets from various commands
Maintains parameter RAM (PRAM)
Manages the Apple Desktop Bus (ADB)
and (naturally) manages the real-time clock

I don't know the technical answer to your specific question, but my guess would be that the battery needs to be good.
(You can still find replacement batteries for those old PowerMacs - https://www.newertech.com/products/pram_4_5v.php )
 
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nzsabuga

macrumors newbie
Original poster
Jul 13, 2020
4
1
Did you test that battery? Might be good! (but probably not) It should be more than 3 volts.
One thing to keep in mind, it is not just a "clock battery"
It maintains certain hardware settings in the system, mainly the CUDA chip. THAT chip:
Turns system power on or off
Manages system resets from various commands
Maintains parameter RAM (PRAM)
Manages the Apple Desktop Bus (ADB)
and (naturally) manages the real-time clock

I don't know the technical answer to your specific question, but my guess would be that the battery needs to be good.
(You can still find replacement batteries for those old PowerMacs - https://www.newertech.com/products/pram_4_5v.php )
I just removed the battery (cos I was worried about it leaking). I've tested it last night, it was only 0.25 volts. I'll probably bodge some AA's into it to test and see if that fixes it (I'm in NZ, so ordering the correct one will take ages to arrive).
 
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DeltaMac

macrumors G4
Jul 30, 2003
10,660
2,883
Delaware
Sounds like a plan! 3 AAs (to make about 4.5 volts) should be good. In fact, some of the replacement "batteries" are just that -- a case to hold 3 AAs, and connector to fit.
 
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nzsabuga

macrumors newbie
Original poster
Jul 13, 2020
4
1
Ok, so got 3x AA batteries, and connected that up, still doesn't work. One thing I've noticed from a couple of YouTube videos of the 5500's is that the after the power on chime (which mine does), after a couple of seconds, the CRT 'thunks' on, and with that, the power LED turns on. Mine doesn't do that part, so I'm gonna have to take a close look at the analog board, cos something on there must be wrong. I might try the easy route, and replace all the caps first.
 
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