iMac G5 A1145: Dead logic board?

[Jose76]

Hi everybody!

I've just got an iMac G5 20" iSight model which didn't start and without HDD (previous owner removed it to keep the data after the iMac failed).

I suspected this was a power supply failure, and as I couldn't find the way to remove the back cover, I followed the ifixit guide and dissasembled the entire iMac.
I couldn't find any blown capacitor anywhere (power supply or logic board). Although I haven't tested the power supply yet, the worst part I could find at first sight is the one in the picture. That's where the logic board gets its power.
I checked the pins with a multimeter and found out that there's continuity between the specified pins. I'm almost certain that this means the board is dead, but, just in case, can anyone confirm this point?

Thank you beforehand

 

[justperry]

Hi everybody!

I've just got an iMac G5 20" iSight model which didn't start and without HDD (previous owner removed it to keep the data after the iMac failed).

I suspected this was a power supply failure, and as I couldn't find the way to remove the back cover, I followed the ifixit guide and dissasembled the entire iMac.
I couldn't find any blown capacitor anywhere (power supply or logic board). Although I haven't tested the power supply yet, the worst part I could find at first sight is the one in the picture. That's where the logic board gets its power.
I checked the pins with a multimeter and found out that there's continuity between the specified pins. I'm almost certain that this means the board is dead, but, just in case, can anyone confirm this point?

Thank you beforehand

Did you study electronics, no I guess not.

Better leave that to someone else, if you don't have schematics you don't know nothing.

It could be perfectly normal.

 

[ybz90]

Hi everybody!

I've just got an iMac G5 20" iSight model which didn't start and without HDD (previous owner removed it to keep the data after the iMac failed).

I suspected this was a power supply failure, and as I couldn't find the way to remove the back cover, I followed the ifixit guide and dissasembled the entire iMac.
I couldn't find any blown capacitor anywhere (power supply or logic board). Although I haven't tested the power supply yet, the worst part I could find at first sight is the one in the picture. That's where the logic board gets its power.
I checked the pins with a multimeter and found out that there's continuity between the specified pins. I'm almost certain that this means the board is dead, but, just in case, can anyone confirm this point?

Thank you beforehand

I would run all of that flux and gunk off with ethanol just in case. It's hard to say whether or not the board is dead or not. I'm not familiar with iMac PSUs; it's just a daughterboard right? Is there a way you can test that separately as well? If you can test either component in isolation from the other, you'll have your answer.

 

[Jose76]

justperry, I found your answer a bit rude (maybe I got lost in translation). Yes, I know something about electronics. I read somewhere that three of that four pins have +12Vdc and the other one is Ground, so, obviously, if there's such continuity between all of them, the board is dead.
I'm just looking for someone who knows 100% what I suspect.

ybz90, thanks for your answer! but the picture is from the iMac's motherboard, not the power supply's one :'(

 

[Graveyard]

Having some continuity on the board doesn't necessarily mean that the board is fried. I presume you checked with a multimeter. If you really have some knowledge of electronics, remember that you cannot check a circuit in a reliable mode. The capacitors, resistors, diodes and so on that are in those circuits will give you some values on the multimeter which might fool you into thinking you have a short or a dead component. The first thing i would do if i were you, would be to check for bad capacitors. Better yet, change all the electrolytic capacitors on the psu and the ones that seem suspicious on the motherboard and hope it's only a capacitor problem. Clean the board to make sure there is nothing left from the soldering process. Then you can check and see if the problem was solved.
Ps: i wish you spoke Romanian so i could guide you properly.

 

[justperry]

justperry, I found your answer a bit rude (maybe I got lost in translation). Yes, I know something about electronics. I read somewhere that three of that four pins have +12Vdc and the other one is Ground, so, obviously, if there's such continuity between all of them, the board is dead.
I'm just looking for someone who knows 100% what I suspect.

ybz90, thanks for your answer! but the picture is from the iMac's motherboard, not the power supply's one :'(

Didn't want to sound to be rude, if you feel offended don't be please, the below Poster explains why I said the above, if you know electronics you know that using a mulimeter on a logic board will most of the time be the wrong way to do so without schematics.

Example, we have a resistor with a value of 100 Ohm, now this value will be the value when you measure it, but almost 100% sure it's not that value on the board, most likely a lot less.
Other components change the values.

If you connect the board to the mains and there is a point on the main board which says it's 12 Volt it should be 12 Volt or Common should be 0 Volts.

Having some continuity on the board doesn't necessarily mean that the board is fried. I presume you checked with a multimeter. If you really have some knowledge of electronics, remember that you cannot check a circuit in a reliable mode. The capacitors, resistors, diodes and so on that are in those circuits will give you some values on the multimeter which might fool you into thinking you have a short or a dead component. The first thing i would do if i were you, would be to check for bad capacitors. Better yet, change all the electrolytic capacitors on the psu and the ones that seem suspicious on the motherboard and hope it's only a capacitor problem. Clean the board to make sure there is nothing left from the soldering process. Then you can check and see if the problem was solved.
Ps: i wish you spoke Romanian so i could guide you properly.

 

[Jose76]

Thank you for your answers.
I guess I must check the power supply first.

If the power supply is dead, can I check the mother board using a regular ATX psu. The iMac's power supply has 5 output pins which come from three different voltages out of the psu's board. As I've found on the net: GND (Black), +12Vdc (Grey), and Brown.

Can anyone tell me if I should provide this brown ones with +3.3V or +5V so I can test the motherboard?

Thank you beforehand!

 

[Graveyard]

If the psu is dead for good, my advice is to get another one from someone that has a broken iMac like yours. Pc power supply units are poorly manufactured these days and you might end up in a worse situation than the one you're facing right now. If you really can't get your hands on an original psu for the iMac, try to find someone with adequate skills to repair the old one. I for one, am sick and tired of using "compatible" power supply units in computers, both desktop and portables. I'd rather work on repairing the original ones whenever possible. And believe me, i've brought back to life plenty of them.