Hi,
I got this iMac for free, and it was said to me that it has dead logic board.
I discovered that the +12VSB came for 3-4 seconds and then disappeared. Hitting the power button for about 20 times, I got it to start up.
Even with the logic board disconnected, the 12VSB was pulsing after few seconds. PSU looked nice with no caps blown. I decided to put my ESR meter on few of the dark green Taicon caps.
I was shocked that one 100uF 35V read 45 ohms, next to it was a 16V 470uF that read almost 4 ohms. These were on the primary side.
After checking the ESR of all the caps, I found two 35V 220uF completely O/C, reading more than a 100 ohms ESR out of circuit, and about 40uF each. Those were decouplers for 24V supply.
There was also on 25V 820uF that read on the high side, so I replaced it.
Now the PSU works like new, I will probably do a complete recap in near future, but I must first replace the GPU in as it is also defective. Also, those light green Taicon caps seem to be much better quality than the dark green ones.
Just my 2 cents, this can help someone
I got this iMac for free, and it was said to me that it has dead logic board.
I discovered that the +12VSB came for 3-4 seconds and then disappeared. Hitting the power button for about 20 times, I got it to start up.
Even with the logic board disconnected, the 12VSB was pulsing after few seconds. PSU looked nice with no caps blown. I decided to put my ESR meter on few of the dark green Taicon caps.
I was shocked that one 100uF 35V read 45 ohms, next to it was a 16V 470uF that read almost 4 ohms. These were on the primary side.
After checking the ESR of all the caps, I found two 35V 220uF completely O/C, reading more than a 100 ohms ESR out of circuit, and about 40uF each. Those were decouplers for 24V supply.
There was also on 25V 820uF that read on the high side, so I replaced it.
Now the PSU works like new, I will probably do a complete recap in near future, but I must first replace the GPU in as it is also defective. Also, those light green Taicon caps seem to be much better quality than the dark green ones.
Just my 2 cents, this can help someone
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