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I have an HP OfficeJet 8600 that won't power up. First it wouldn't turn off, but after doing a standard partial reset described on several websites, it now refuses to turn on. Took the CMOS battery out, verified it was good with a multi-meter, and had it out a good 45 minutes, so anything that can be reset/cleared by removing it for a few minutes definitely was.

Took the power supply out to meter it, and that's where my confusion begins. If you look at the label on the PS in the attached image, you'll see that it accepts anything from 100 to 240 volts AC and puts out either 32v DC or 12v DC. The power supply connects to the printer's mobo with a 3-pin molex connector, and its pin config is diagrammed on the label (top right corner). It shows both voltages being delivered on the right pin, ground on the middle pin, and a crescent (sleep mode?) on the left pin.

This would make sense to me if each voltage was delivered on a separate pin, but I wasn't aware you could have more than one on a single pin, which apparently is the case here. When I meter the pins, I get 32.5v across right pin and ground (middle). I get 30.3v across the right pin and the crescent (left) pin. I get 2.2v across the crescent (left) and ground (middle). I don't get 12v anywhere.

Does this make sense to anybody, and if so, can you explain to me how it works? I don't think I can declare my PS good or bad w/o first testing the 12v path to see what it reads, but how to I do that?

enter image description here

Thanks, lunchbeast

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    \$\begingroup\$ I think that the third pin (left most) must be a control pin. Presumably when in sleep mode (hence crescent moon) the connected device will either pull this pin high or low to change the voltage down to 12V to save power. \$\endgroup\$ – Tom Carpenter Sep 3 '16 at 4:05
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    \$\begingroup\$ Also, under no load the supply voltage will float up a bit, so it's not at all unreasonable to measure 32V rather than 30V - it's within 10% so I wouldn't be concerned with that. \$\endgroup\$ – Tom Carpenter Sep 3 '16 at 4:07
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    \$\begingroup\$ I'd try connecting the left pin to ground with something like a 1k resistor (much less likely to cause damage than just shorting it with a wire if I am wrong about the function of the pin), and then see if it drops down to 12V. Also while you are at it, put a 1k resistor across the 30V/GND pins to act as a load and see if that helps it regulate to 30V properly. \$\endgroup\$ – Tom Carpenter Sep 3 '16 at 4:09
  • \$\begingroup\$ PSU would be a more obvious abbreviation for power supply. When I read PS in association with a printer, I think postscript, and don't bother clicking through to the question... \$\endgroup\$ – Sean Houlihane Sep 3 '16 at 9:35
  • \$\begingroup\$ I think Tom has it. To get 12V out, you need to do something with the Sleep pin, and only H-P know for sure what. But grounding it (via 1K for safety) is a reasonable first guess. \$\endgroup\$ – Brian Drummond Sep 3 '16 at 10:36

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