Device: 2004 17 inch iMac G5
Symptoms: No power up, bulged /leaking mainboard and power supply capacitors
Repair: Replace electrolytic capacitors in mainboard and power supply. Replaced 24vdc power regulator in power supply.
Located and eliminated two through hole pad shorts between the 12Vdc+ and ground layers of this multi-layer main board. Repair complete.
The replacement of the voltage regulator in the power supply corrected the low voltage on the 24 volt output. After assembling the system again, we still have a no boot. Diagnostic LED's #1 and #2 do light up, along with the hard drive but no farther. After doing some voltage checks on the mainboard, I found no voltage at the capacitor array serving the processor and memory. Further testing showed a short to ground in this circuit. Will use low voltage, low current to power this circuit and attempt to locate the short using the voltage drop method.
This was by far the most difficult board I have ever come across to desolder components from. I don't know what the exact formula was for this lead free solder, but this stuff would not melt. The leads of the original caps were also very thin compared to the new replacements (a plague counterfeit?) which caused some issues with the leads breaking during removal and requiring hand drilling to get them removed from the board.
Mainboard removed from system
Parts ordered, power supply ready for its new caps.
The majority of the capacitors in the power supply are produced by Ltec, a Taiwan based company and known for low quality components. The capacitors outlined in red are all bulged and/or leaking. All of the electrolytic capacitors will be replaced with high quality Panasonic or Nichicon equivelents except for the two large filter capacitors as both tested within specs, showed no signs of bulging or leaking and generally don't fail too often.
The capacitors circled in red have failed, evident by the bulged and leaking tops. All 25 of the Nichicon electrolytic capacitors will be replaced with new production Nichicon exact replacements.