HP Laserjet 4100 repair

[iJoseph2]

In addition to the 4100 I've also got an Oki MC363 - absolutely brilliant multi function printer and I really like the fact I can scan documents straight to a USB stick (mostly what I use it for). But it is expensive to run and after I just paid 50 quid for a replacement black cartridge that can only print a couple of pages before I need another.. I really needed to sort out my 4100.

I've not actually finished this repair yet - mainly because I've just been reunited with an older 4050 and also I got fed up dealing with these heavy bulks. So it'll have to wait until later maybe Christmas. But I think I finally got to the bottom of these jamming issues.

Photos attached of some of the pertinent areas of a parts donor (while I was buttoning it back up to put away).

Faults with my 4100

1. Tray 2 paper size buttons intermittent. Intermittently changes to JISB5. I'm guessing mid way through a print the paper "changed size" and the uP got confused and said "paper jam".

2. Paper registration flag spring dislodged. Guessing the slow/sloppy movement didn't register and the timing of signals was out causing "paper jams". There's three flags in the area and I replaced all of them.

3. Tray 2 solenoid/solenoid drive electronics faulty - I've not actually finished diagnosing this one as I have to take it apart again.. but I know what I'm looking for now. Next step check the solenoid pad material in case its sticky.

4. Optional tray PCB dead (tray not detected by the printer). No shorts that I can find. No idea what I'm looking for so will probably power it up and check the 4MHz crystal and hope it's just that.

5. Optional tray solenoid sticky thus delaying the release and paper timing is out causing "paper jams".

6. Swapped a lot of opto sensors but now I think this was a waste of time. Either way I cleaned up certain ones as I was in the area in case of dust/debris.

7. Page covered in grey streaks - pretty sure this started when we had a heat wave here in the UK. The print quality was absolutely perfect one day and the next time I used it it was awful. I didn't even open the lid or do anything.. literally turn off printer.. then turn back on a week later and problem appears. Thanks to this forum I suspect its the wiper blade.

https://www.eevblog.com/forum/repair/hp-laserjet-drum-problems/

[iJoseph2]

Photos

[iJoseph2]

Photos

[iJoseph2]

Photos

[MathWizard]

For for #1, it might be a dirty or worn out switch. Or maybe some capacitor is wearing out and can't maintain a high enough voltage? If it was more like switch bouncing, you should notice problems like having to press the button a few times, or a certain way, and normally settle down pretty quick, not halfway through a page.

I'd want to know where the voltage for that switch comes from, and how it relates to some monitoring MCU. The digital input/outputs on IC's wear-out too.

Do you have an oscilloscope ?

Yeah it's always good to look for mechanical problems, like friction, or even the some plastic housing moving more than it should. But on the electrical side for the solenoids, I can easily imagine some drive circuit wearing out. Even just a resistor, cap, diode or BJT going bad could do it.

Here's the datasheet for the MCU on the optional-tray-PCB

[R.J.]

Do you have a Service Manual?
When you have, surely check the Troubleshooting process...

Check also the "Engine test" by pressing the button with a small long stick at the left side of the printer just below the fan vent.
Tray 2,3 or 4 must be installed and loaded with paper and there must be a tonercartridge in the printer.