asked Jan 10, 2008 at 10:11am
Hp HP LaserJet 4M

HP LaserJet 4m: power supply issues

What makes these power supplies go bad -- can it happen if a printer sits too long without being used? I haven't used my printer in more than 2 years, and it received hardly any use in the previous 8 years. I installed a new toner cartridge last week, turned the power button on, and *poof*, nothing - no power. With the help of the terrific archives at this website (thanks, Moe!), I've managed to open up the printer, remove and examine the power supply, and peek and poke around inside. The power switch works properly. When switched ON, after about 1 second, I can hear a small "click" from inside the printer and the blades of the fan spin/flutter very briefly, and that's it.

- Is it always the entire power "module" that goes bad and needs replacing, or is there any sort of small part or item inside that could be adjusted or replaced somehow? I'm a novice with electronics :) -- I've looked inside the module and things appear very clean and intact, nothing broken or burned-out-looking... obviously that could be meaningless.

- Is there any way to carefully test the power module, like with a voltmeter or something, to verify that it IS the source of the problem?

Thanks for any advice, and good luck with your printers!
There aren't any schematics available for them. There also aren't any new power supplies either. If you click on my name and email me, I can provide you with a working, tested power supply. There really isn't much of a problem with them failing. I can only remember replacing a handful of them over the years.
by moe on Jan 10, 2008 at 10:29am Add comment
sounds like dried-out electrolytic caps problem. a very common problem with switch mode power supply board with age.

the only question is, which ones?

from my experience with power supply "in general", usually a high voltage cap(450v for country with 220-250v main ac)around 1-4.7 uf range in the primary side.

and also quite often the filter caps before and after the voltage regulators like the 12v and 5v rails needs to be replaced too.

good luck.
by tk55 on Jan 10, 2008 at 1:02pm Add comment
Thanks for the responses, guys. I appreciate your help!
by FrugalPrinter on Jan 12, 2008 at 11:16am Add comment