Hello. I am trying to repair 710w psu from Power Mac G5 A1177. I know these are cheap on ebay and i take this mostly as learning experience.
This unit has darkened pcb near 12volt output. Seems like some sort of clamping circuit that connects 12v to gnd and it seems to be controlled by circuit built around lm393 dual comparator ic. I guess this is sign of overvoltage on 12v output. Another really visible issue is really burned R49 located right next to row of optoisolators and i have no clue of value used to be. Any hints and help is appreciated. Especially value of R49.
There is old post with exactly same issue here: https://68kmla.org/bb/index.php?threads/powermac-g5-dual-core-2-3-psu-repair.43383/ and answer to last question there is that there are resistors for circuit i mentioned earlier on other side of the board. R49 is actually also used in very simlair way but i haven't yet been able to trace what it actually does. There fet (i think) that connects something to ground via it and it propably was relatively beefy 1w resistor judging from size.
This unit has darkened pcb near 12volt output. Seems like some sort of clamping circuit that connects 12v to gnd and it seems to be controlled by circuit built around lm393 dual comparator ic. I guess this is sign of overvoltage on 12v output. Another really visible issue is really burned R49 located right next to row of optoisolators and i have no clue of value used to be. Any hints and help is appreciated. Especially value of R49.
There is old post with exactly same issue here: https://68kmla.org/bb/index.php?threads/powermac-g5-dual-core-2-3-psu-repair.43383/ and answer to last question there is that there are resistors for circuit i mentioned earlier on other side of the board. R49 is actually also used in very simlair way but i haven't yet been able to trace what it actually does. There fet (i think) that connects something to ground via it and it propably was relatively beefy 1w resistor judging from size.