asked Sep 3, 2011 at 4:41am
Hp HP LaserJet 6L

HP LaserJet 6L problem with sensors?

Hi! I had to attend to HP LJ 6L printer recently. It's been printing very erratically for a while, sometimes only the page sent first, repeatedly (odd one!) and since it's kinda old and looked very dusty I decided to clean it up. After I reassembled it having thoroughly vacuumed the dust out of the PCBs, it starts with following light sequence: first lights up the bottom LED (green), then it goes out for middle one (green as well), which immediately turns out for constant top orange. If I hold the button below, sequence repeats, then (still holding it pressed) bottom LED briefly turns green and top orange lights up, no middle one this time.

I have checked all three sensors, they are held by springs in position as to be tilted by paper movement.

What could it possibly be? I for once thought I have misplaced the wiring while doing reassembly, but having checked with the service manual diagram, looks like those are proper placed.

There's no motor action, whether with toner or without it. Now I do not assemble it completely, leaving tha back cover off - I hate those plastic fasteners. Any help or advice appreciated! It's not mine, so I'm kind of got to make it work:)
Thanks in advance!

With respect,
The old saying if it ain't broke do not fix applies here. You took a working printer (maybe some small issues) and broke it. By your post you have no idea what you are doing so all I can tell you if no ready light and no motor action, then the printer thinks it has a paper jam. Most times the exit sensor FLAG in the front of the fuser became dislodge by your attempt to FIX the printer. Check out the bottom picture.
by dmzcompute on Sep 3, 2011 at 9:18pm Add comment
Yes, you are right, it really did. While reassembling I unintentionally took it out and then put it back, it now looks like the one on the picture.
What WAS the problem I can't tell, but it persisted through two PCs to which the printer was connected. It simply did not print anything but the test page, that gave idea there was dust on board short-circuiting some circuit (I was thinking of memory).
And of cource you are right about no-idea. But I am in Russia, fixing or even cheking this printer in service center is completely impossible task - it would be up to 10 times cheaper to buy new one, and that I cant afford at moment. The printer belonged to several people. Last few years my dad was printing his lectures and studies on it. The initial problem appeared gradually.

I'll check again the exit sesor flag. Sorry for my English btw.
Just not sure if the LED sequence might indicate some more serious or simply different problem.
by getmenot on Sep 4, 2011 at 3:30am Add comment
There is a spring attached to that FLAG which causes it to be in the up position at all times except when paper flows over it. If not in the up position the printer thinks there is a jam.
by dmzcompute on Sep 4, 2011 at 9:50am Add comment
Yes, I tried to secure the other end of it in two different positions, both of them causing the flag to be up - seems like that's not the issue. As I got it, first paper sensor flag is held in position by gravity alone, while second and exit sensor flags are springed. they all seem to be ok, actually, everything with this printer seems to be ok apparently except that it's stuck with error on front panel.
The only thing I'm not quite sure now about the sensors and their flags is that the second (registration) sensor flag doesn't seem to quite shade the diode/receptor pair. Its other arm is pressed against the black rubber ring (there's pair of them on the white part-axle) and that seems to prevent the shader part of flag to fully cover the sensor (it only reaches the line of sensor aperture by it's edge, less than millimeter. However looks like that's normal for that assembly?
I did not mention that I put some non-aggressive grease onto the plastic gears on the side (it was very noisy, and I didn't like the quality of the noise). Maybe this did the trick and some needed conductunce is lost thus?
I double-checked the wiring again, can't imagine what can be wrong there.. else is the electric component failure, to my mind. If so, it's a piece of junk for now - until the awareness of which one exactly and the spare falls on me from above:)
by getmenot on Sep 4, 2011 at 1:28pm Add comment
if you mean the 2 black "plastic" free-rolling roller, one on each side of the paper pick up roller, and the white part-axle being the paper pickup roller shaft assembly, then no, that sensor arm when it's on up position shouldn't be touching anything.

if the machine think that any of the 2 sensor arm is in the down position it will say paper jam.

perhaps you didn't re-assemble the paper pickup roller shaft assembly correctly? the 2 plastic rollers should be resting on the 2 side-pads besides the main separation pad. and the 2 locking arms on the outermost. (yes, they should be locked onto the rear vertical plate when properly assembled. if they swing up and down on the shaft it's wrong).
by seriously on Sep 4, 2011 at 3:52pm Add comment
OK:) guess I got something moving on. I did not touch that flag assembly at first.. but as you point out, I found in SM that thing is called Feed Assembly. Is it what we are talking ablout?

the two black rollers on an axle (Idle Roller?) one side of which connects to gears by a shaft held by a medium-sized pinion, and one of them is touched by the triangle-shaped arm of the Registration Sensor. When I press roller while holding Feed Assembly in hand, the sensor flag would cover the sensor gap almost completely. however, when assembled (tried several times) nothing seems to press it the same way, and the flag is almost NOT covering the sensor aperture. So to check this out, I put a bit of non-transparent sticky thingy so as to elongate the flag.
Amazingly, now printer makes some motoric noise, and stucks with all 3 LED steady. so i press the button, and only bottom and upper remains.

Continuing to battle)

Any advice?

With respect,
by getmenot on Sep 5, 2011 at 2:09am Add comment
That is a fuser error. Recheck the two connectors from the fuser to make sure they are secure. One on the right side that goes towards the back and one on the left side front that fits into a small white connector.
by dmzcompute on Sep 5, 2011 at 8:42am Add comment
Now, you guys are miraculous!
It's printing again, and daddy will be able to work on his monography as he intended, and our short money are safe for something more agreeable than printer upgrade..
Thank you, I'm kind of out of words actually to express my feelings exctly, as I thought hope is sleeping away to somewhere very profound.

The sensor flag I left inside with the tune-up sticker, and it was the smaller fuser connector which was slightly out of place which gave the further error. And the non-printing issue which started it all was again my hurry in reason - with PC upgrade the motherboard had only jumpers on it, not the actual LPT, and I connected the extension port cable just the other way around. Guess there are some mirror contacts in DB25 LPT connector, for it sent some commands to printer but did not print - only the test page which is stored in printer I suppose.

Thank you very much again for your help and attitude!

With deepest respect,
by getmenot on Sep 5, 2011 at 11:32am Add comment