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gwb21471

macrumors member
Original poster
Jun 12, 2023
90
17
I bought a Macintosh Performa 550 off of facebook for 25.00 because he couldn’t get it to turn on. After I got it home took out the motherboard and found out the battery was dead but didn’t leak. The motherboard was very clean like new. So bought a new battery for it. Took the cover off the the monitor to check the power board and was very clean inside too. All the capacitors was in great shape. So I put it all together and put the new battery in. Plug it in and turn on the switch in the back. You can hear the power supply power on. But when you hit the switch on keyboard it will not turn on. Does anybody know what could be causing this? I get not chime or anything. I took out the simm any video ram out to make sure it wasn’t that and still won’t turn on. What else can I check? Thank you for the help.
 

chabig

macrumors G4
Sep 6, 2002
11,349
9,048
It seems as though the motherboard isn't getting power. Connections tend to be more reliable than components, but you could check the connectors between the power supply and motherboard. If they are good, get a multimeter and make sure the power supply is putting out good DC. If you're lucky, it might be a failed power supply, which you should be able to swap if you can find one.
 
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gwb21471

macrumors member
Original poster
Jun 12, 2023
90
17
It seems as though the motherboard isn't getting power. Connections tend to be more reliable than components, but you could check the connectors between the power supply and motherboard. If they are good, get a multimeter and make sure the power supply is putting out good DC. If you're lucky, it might be a failed power supply, which you should be able to swap if you can find one.
Do you or anybody know if there a diagram of the power supply out there? I did do a search online but I don’t get anything.
 

davisdelo

macrumors regular
Jul 7, 2019
125
168
Fort Worth, TX
It sounds like you check the motherboard pretty well, but did you look for broken soder joints? They can be hard to find. It might be worth taking that multimeter to each one in the power path to see if the fix is a simple reflow somewhere.
 

gwb21471

macrumors member
Original poster
Jun 12, 2023
90
17
It sounds like you check the motherboard pretty well, but did you look for broken soder joints? They can be hard to find. It might be worth taking that multimeter to each one in the power path to see if the fix is a simple reflow somewhere.
I going to do that check the motherboard. I know the guy i got it from had the capacitors replace 6 years ago on the motherboard and replace two for the power supply at the same time. All i know is that it was working one day and the next day the guy told me it won't turn on. so it sat in his basement for 3 years and figure he would sell it. I know his basement must been damp since some of the metal has light rust on it. Well thanks for the help i am getting since there not much online about this model. Everytime i look online i just get the specs about this and i get the LC 550 model instead.
 

gwb21471

macrumors member
Original poster
Jun 12, 2023
90
17
Well found no cracks in the solder. But found corrosion on the connectors on the analog board. Clean that up and now they shine now gold like before. Blew out any dust I saw. Blew out the connectors with electrical cleaner. After the glue drys on the screw holes that was crack I going to give it a try.
 

gwb21471

macrumors member
Original poster
Jun 12, 2023
90
17
Well found no cracks in the solder. But found corrosion on the connectors on the analog board. Clean that up and now they shine now gold like before. Blew out any dust I saw. Blew out the connectors with electrical cleaner. After the glue drys on the screw holes that was crack I going to give it a try.
Well the power light comes on and I get a noise out of the speakers. I think it trying to chime but just a noise. So have to figure what’s wrong. The screen doesn’t come on. But this is a start. Thanks everyone for the help here.
 
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