Gi4zoasked Dec 24, 2017 at 3:55pm
Demo page blank; Engine test page blank; Image Engine test page on transfer belt
HP Color Laserjet 2500n
The printer ejects blank demo pages. The printer ejects a blank page when executing engine test. During engine test there is an image on the transfer belt. (Clearly visible but I admit it moves pretty fast and consisted only of some thick lines and some circle sections).
(I know this because 1) I have removed all covers 2) I tricked the top cover switch (at the left) and the laser assembly shutter switch (at the right) using elastic strings 3) I opened the imaging drum in such a way that I can see the transfer belt while printing).
I conclude the secondary transfer roller is not functioning.
The only spare part I have is another imaging drum.
The printer is equiped with a JetDirect card which can be interrogated using a computer via ethernet.
Is my conclusion correct?
How should I proceed?
Haven't worked on one of those in years. Not a transfer roller issue. Most likely cause is either the carousel is out of alignment or the carousel brake release solenoid is sticking. It is located on the top right of the printer. You can realign the carousel by pulling out on the large gear on the right and lining up the index marks. This video shows a 2840 which is a 2500 with a scanner on top. https://youtu.be/xKwsYipQ0Ag
The solenoid was sticking however I have solved this problem (before posting) and the pages produced were still blank.
I completely believe you however if there is an image on the transfer belt shouldn't it be transfered to the paper?
Any way to remove my second posting of this question?
If there is an image on the belt, then it should be transferred. A better way to see if there is an image is to do the demo page from the manual tray. When the back end of the page enters the printer, quickly open the door and take out the transfer belt and see if there is an image on it.
On the left and on the right hand side of the printer the alignment marks on the small white wheel (cylindrical extensions approximately 2 mm high, 1 mm diameter) are two teeth off the alignment mark on the black wheel (a line on the circumference of the wheel, parallel to the axis of the wheel).
I have also interrupted printing a demo page and made a picture of (part of) the transfer belt, clearly showing a thick (approximately 4 mm) red line. I repeat this line is not printed on the demo page (which is blank).
Perhaps even an equal misalignment causes problems however any toner on the transfer belt should be transfered to the paper. So at least there is a problem with this transferring (by the secondary transfer roller).
Before addressing the misalignment problem (if any) I want to solve the transferring problem. How do I proceed?
How do I post pictures?
Let"s try an engine test page. That eliminates the logic board and prints a page of vertical lines. To do one, reach above the manual tray on the left side and feel around for a floating piece and push up on it. The printer needs alignment and you can't troubleshoot properly until you do it. It isn't that hard as all you need to do is pull out on the large gear and line up the marks.
If you need to post images, you can post them free on imgur.com and post the link here.
I have performed an engine test before posting. It was blank.
Upon Moe's suggestion I have retried performing an engine test. After a paper jam I have the error message "INCORRECT YELLOW CARTRIDGE" after which the printer halts. (The paper jam was caused by not reinstalling the metal cover over the secundary transfer roller when executing the engine test. I have installed it now but the error remains). A restart, a cold reset and a NVRAM initialization did not clear the error.
A picture of the transfer belt when printing a demo page: https://imgur.com/BjU4cWA.
Two pictures of the alignment (right and left respectively) : https://imgur.com/rKezkhh.
Correction on the links to the pictures:
Image on the transfer belt when printing a demo page:
Alignment carrousel right hand side:
Alignment carrousel left hand side:
I have performed the alignment: First I aligned the right hand wheel (by 2 teeth). Thereafter inserting the toner cartridges was more difficult and the printer gave status error lights on all the cartridges. Second I also aligned the left hand wheel (by 2 teeth). Thereafter the status error lights did not show up.
FOR THOSE WITH ALIGNMENT PROBLEMS: Aligning was not that difficult. Needing a couple of attempts and visual checks it took all in all about 30 minutes. It is done by applying a force at the rim of the black wheel parallel with the axis of the caroussel and , of course, away from the side the wheel is. A screwdriver can be used. As soon as the black wheel and white wheel are no longer engaged they can be moved with respect to one another. After that take away the force. Sometimes a little juggling is necessary to have them engaged again. Hardest is to see if the relative motion is just about enough.
Then I executed several demo page prints and engine tests. The results varied: On most there were some clearly visible but nog bright yellow -mainly in vertical yellow streaks. Yellow streaks were also visible on the drum. There were never any other colors. On the transfer belt though there were -per page- bright horizontal lines, probably one for every color. Also was there a yellow area. On the last print there is a very faint image consisting of some black lines forming squares.
So the situation has improved (thanks to moe convincing me). For the time being the printer can not be found using Ethernet which is a disadvantage since now there are no error codes detectable that way.
Should I be checking the several high voltages by now?
The yellow streaks sound like they are coming from a bad drum wiper blade. Horizontal lines are usually caused by intermittent loss of high voltage. Those come from faulty drum contacts. To explain, the drum is charged with high voltage through the contact. The laser erases the hv wherever an image is supposed to be. Therefore, as the drum rotates and the contact loses hv, the result is a horizontal line at that spot as the toner is applied where there is no hv and repelled where there is hv since it has a like charge.
Thank you for the offered explanation of the yellow streaks and of the possible horizontal lines.
(I had not reached these conclusions and they are useful for diagnosis. By the way I do however understand the principles of laser printers -thanks to a decent education in electrical engineering and the Internet).
So probably the wiper blade is bad. But still unexplained are:
1) The absence of other colours on the drum (but during one start up the transfer belt was covered with complete areas of solid blue, magenta, black and perhaps yellow. I can not repeat this occurence though).
2) The lack of transfer of the several -I think 1 for every cartridge- bright, approximately 5 mm wide horizontal, coloured lines on the transfer belt to the paper
I suspect lack of high voltages.
1) I have taped the high voltage contact on the yellow cartridge. No noticable difference on the transfer belt and paper (to be expected because this way even less toner is transfered to the drum)
2) I have taped the 4 high voltage contacts on bottom of the drum (after removing the tape on the yellow cartridge). Not much difference on the transfer belt and paper (not to be expected because this way more toner should have been transfered to the drum)
Measuring directly is inconvenient. I do not have a spare PCB on which the high voltage circuitry resides.
At this moment I have barely a clue as how to proceed.
The high voltage must be operating or everything would be blank. There would be no toner transferring to the transfer belt. The PCB only sends out the hv, it can't send it out to the belt, but not the secondary transfer roller. You mentioned a metal cover over it. The metal piece in front of it serves as a guide for the paper and I don't know why you removed it. The roller's function is to charge the back of the paper and pull any toner off of it onto the paper. I' ve never seen one not getting hv, but I have seen them in other models where the spring mounts were broken and one where the roller was actually laying loose at the front of the printer paper parh.
I did remove the transfer roller plate then to inspect the transfer roller and the contacts used to apply a voltage to it. (It turned out the left spring was out of position 1-2 mm at its bottom. Otherwise it looked fine. I corrected that but the printer still printed blank pages). For a picture of the transfer rolle plate and surroundings at the moment see: https://imgur.com/RbFwYC8.
Moe's comment about the functioning of the HV makes sense. Probably at least some voltages arrive at developing cylinder, drum and primary transfer roller. However since the voltages differ there must be running several wires.
I have just checked the alignment and it is still allright.
Perhaps important to know I have been working on the low voltage PCA, which is next to the high voltage PCA.
The reaseon is there have been -and still are- problems with the fuser current control circuit. The triac controlling the fuser current was a an open circuit. I replaced it. After that there was error 50.3 (very likely fuser too hot). I checked the triac but the triac was functioning. I have used resistors to lower the resistance in the circuit with the two temperature dependent resistors (actually NTC's) in the fuser which had no effect. Therefore I suspect the fuser current control circuit. Next I used and still use a power resistor (actually hot air gun, approximately 50 ohms) in series with the fuser. This allows me to print one page before 50.3 reoccurs.
Now I have no idea what to investigate next.