How do I test this AC adapter? - Page 1
Forum section: electronics / repair

author: ajmcgraw
author_rank: Newbie
timestamp: June 18, 2021, 05:06:35 pm
content: 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?Thanks.

author: themadhippy
author_rank: Super Contributor
timestamp: June 18, 2021, 06:00:56 pm
content: could it be the moon connection is telling the power supply sleep mode has been selected so only give out 12v

author: james_s
author_rank: Super Contributor
timestamp: June 18, 2021, 06:09:09 pm
content: 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.

author: ajmcgraw
author_rank: Newbie
timestamp: June 18, 2021, 07:35:54 pm
content: 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?

author: Ian.M
author_rank: Super Contributor
timestamp: June 18, 2021, 07:58:34 pm
content: Safe to say its good. That's exactly the behavior you'd expect of a standby supply that cycle skips when its minimally loaded.

author: ajmcgraw
author_rank: Newbie
timestamp: June 18, 2021, 08:09:03 pm
content: Quote from: Ian.M on June 18, 2021, 07:58:34 pmThanks. Wishful thinking on my part, then. I was hoping I could just swap out the power supply and celebrate an easy fix.

author: james_s
author_rank: Super Contributor
timestamp: June 18, 2021, 09:15:14 pm
content: Open up the printer and check the voltage with the power supply connected, it's still possible it's a relatively easy fix. I fixed a "dead" scanner someone gave me once, turned out the power LED and the USB cable had both failed. The scanner was turning on, it just didn't look like it was.

author: tunk
author_rank: Super Contributor
timestamp: June 18, 2021, 09:39:25 pm
content: Or the on/off switch has died.

author: aqibi2000
author_rank: Regular Contributor
timestamp: June 19, 2021, 12:31:53 pm
content: If you want to remove some of the fluctuating then measure the voltage with some load

author: howardc64
author_rank: Newbie
timestamp: December 17, 2023, 01:54:38 am
content: Have a similar HP printer (OfficeJet 5740) PSU (image attached) Same 3 pin PSU interface but not same model # as OP. Printer doesn't boot all the way. Display either blue screen with a code or vertical lines. Here are the PSU measurementsPSU standalone testing32v/12v line = 32.8v DC stable no AC componentcrecent moon = 2.74v DC stable no AC componentJumper crecent moon to ground with 1k/4.7k/10k resistors all change 32v/12v line to 12v but continuously drop 1v every 1-2s and I stop testing after 6v (continues to drop but I just stop testing)PSU plugged into printer. Presumably this is with load32v/12v line = 32.8v DC stable no AC componentcrecent moon = 2.74v DC stable no AC componentNever triggers to 12v. Presumably printer never boots far enough to then eventually go to sleep mode.Probably the PSU should be good enough for the printer to boot completely? Thus my fault is likely internal to the printer.