From Apple, for QuickSilver:
1) Connect Mac with a known-good cable to a known-good GPO. Make sure that the PSU loom is firmly in place (break and remake) at J23. Switch on the GPO. Do not start up the computer yet.
2) Connect voltmeter black to pin 11 of the 22-pin PSU connector. Red should measure near 'nuff to 25V (TRKL) on pin 22. If 25V is present, the PSU is probably OK. Check again after verifying your connections if you don't find 25V. If still no 25V, replace the PSU.
3) Start up the Mac. Does the fan spin? If not, replace the PSU.
4) See whether there is 3.3V between pins 11 (black) and 1 (red). If no 3.3V, replace the PSU.
5) See whether there is 5V between pins 11 (black) and 4 (red). If no 5V, replace the PSU.
6) See whether there is 12V between pins 11 (black) and 10 (red). If no 12V, replace the PSU.
If the PSU passes these tests, it is not the cause of 'no power-up'. If you wish to use a 'minimal system' for these tests, disconnect the HDD(s), keyboard/mouse and external devices before you begin. All the QS needs in this minimal mode is PSU, MLB (with RAM and CPU), speaker and power button.
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1) Connect Mac with a known-good cable to a known-good GPO. Make sure that the PSU loom is firmly in place (break and remake) at J23. Switch on the GPO. Do not start up the computer yet.
2) Connect voltmeter black to pin 11 of the 22-pin PSU connector. Red should measure near 'nuff to 25V (TRKL) on pin 22. If 25V is present, the PSU is probably OK. Check again after verifying your connections if you don't find 25V. If still no 25V, replace the PSU.
3) Start up the Mac. Does the fan spin? If not, replace the PSU.
4) See whether there is 3.3V between pins 11 (black) and 1 (red). If no 3.3V, replace the PSU.
5) See whether there is 5V between pins 11 (black) and 4 (red). If no 5V, replace the PSU.
6) See whether there is 12V between pins 11 (black) and 10 (red). If no 12V, replace the PSU.
If the PSU passes these tests, it is not the cause of 'no power-up'. If you wish to use a 'minimal system' for these tests, disconnect the HDD(s), keyboard/mouse and external devices before you begin. All the QS needs in this minimal mode is PSU, MLB (with RAM and CPU), speaker and power button.
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