Power supply repair number two, for me, is repairing a unit I’ve had for years, and “works”, but frequently, it will power up the the computer, then almost immediately power it back off, and require flipping the switch on the power supply off and on to get it back “working”. This behavior is indicative of either the Over or Under Voltage/Current latch kicking in (this could be semi-confirmed by unplugging fans, or hard drives from the power supply, and it would start up much more reliably). If the unit did successfully power up, it would run the computer with no problems for weeks/months at a time (I had the unit powering an IPTV box for 6 months previous to teardown for repair). Testing with my Dr. Power II shows everything is fine, but the tester only puts a couple ohms of load on the unit. Real testing requires an actual PC load (or a much larger load than I can provide with my Reload:Pro). Opening the unit, I found that several of the solder joints between the output wiring, and the “jacks” for attaching cables looked “cold” or “dry” (meaning, non-good solder connections) (See picture here). This can certainly lead to protection kicking in on devices. Reflowing these connections took a bit of time due to the thermal mass of the wiring and connection board, but after, the connections did look much better. Testing again showed everything was fine (as before). Hooking the unit back up to a real PC showed consistent power up. Calling this one fixed, for now.
Couple weeks back I got a request to repair a friends computer. It would lock up, not reboot, etc. The computer was largely for gaming, so after an initial software scan, I figured it must be heat. Opening the machine, I noticed none of the case fans are running. I had initially done the build on the machine, and new all the case fans were wired to the fan power “bus” provided by the power supply (which handled speeding/slowing the fans based on case temp), an Antec TruePower Trio TP3-550. Asking the friend, he mentioned that he had noticed the LEDs on the front case fan had went out a month or two ago. Hmm. Checking the voltage on that fan bus showed only 2V (not nearly enough to run a 12V 120mm fan). The PSU’s fan was also not running. Crap, that was probably overheating the PSU, and causing the instability.
Wanting to get his machine back up and running, I picked up a replacement Corsair power supply, installed it, and got him on his way. Then, I went to repairing the Antec power supply. Warning, because this is a power supply, and especially because this is a high wattage switcher, there are dangerous (and lethal if you live in parts of the world that run off 220/240 household) voltages inside. Make sure the unit is unplugged, off, and even give it an hour or two for the primary caps to discharge. I have seen the primary discharge relatively quickly, so there must be a bleeder resistor in the unit, but I didn’t bother tracking it down.