Electronics > Repair

How do I test this AC adapter?

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I have a printer that won't power on, and I'm trying to test the power supply (picture below) before I buy a new one.

From ground to the left pin, I get 32.3V on my multimeter, but what is the pin labeled with a crescent moon? My guess is it's some kind of standby power out, but how would I know what it should be? (did lots of searching with no luck) It measures at 0.593V.

Also, is there any way to test the 12V option?


could it be the moon connection  is telling the power supply sleep mode has been selected so only give out 12v

I think that's likely. The power supply is rated for two different voltages on a single output, there must be a way of telling it what voltage to put out. My guess is it's something simple, you could try grounding the sleep pin and see if the 32V output changes to 12V. If grounding it doesn't work then my next guess would be pull it up to 3.3V.

I would expect though that if it's putting out 32V right now the power supply is probably ok. You might test it under load though and see if it sags. Best way is probably to open up the printer and plug it in, then measure the voltage at the printer.

Thanks to you both! That is indeed what it is. Grounding the sleep pin gave me a output voltage near 12V, but it is not stable.

On the MM it was oscillating between 11.23 and 12.45 volts. I hooked it up to a scope, and it looks like a straight DC line that gradually drops from 12.45V down to 11.23V. After the trace drifts down to 11.23V, there is a very sudden and visible ramp up that almost immediately takes it back up to 12.45 and then the trace drifts back down to 11.23 again before the next ramp up. This pattern continues indefinitely.

Safe to say the supply is bad?

 Safe to say its good.  That's exactly the behavior you'd expect of a standby supply that cycle skips when its minimally loaded.


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