Jpoazasked Jul 1, 2015 at 9:02am
HP LaserJet 4
HP LaserJet 5MP 3 LEDs flash when applying power
My HP LaserJet 5MP printer has been an incredible workhorse since I purchased it way back in 1995. I have a problem that I hope I can easily fix with your help. When I power the unit on, LEDs 1, 4, and 5 light up for a second, then go off and nothing happens. I also hear a very slight sound ("thunk"), which I'm guessing is a fuse (auto-resetting) tripping. I have taken the unit apart, removed and re-seated the memory module then (probably just a fluke) it restarted 2 times. Since the motor started those 2 times, I don't think that's the problem. On all of the failed start-ups, it's not even going through the routine LED sequence before failing and powering down (so it's not even getting to the part where it powers up the motor). It's hard to find all of the 5 MP-specific information in the repair manuals, as there is both a "combined" manual which I cannot locate, and then the updates for the 5MP. Any help would be greatly appreciated as I have never had a problem with this incredible printer. Thanks!
First thing I would try is replacing the control board. I' ve seen a lot of them go bad and fail to power up the printer. Usually, flipping the switch on would do nothing when they fail.
All of the circuitry that controls power is on that board. Last week, I saw this laser printer for $29.95 and it had a $20 gift card with it, making the effective cost $10 It's now selling for $49.95 with a 2 year guarantee. 3 times as fast as the 5mp and it is wireless, even works with your smartphone. The starter cartridge supplied with it is good for 700 copies.
HP LaserJet 4