|HP CP1515n Color Calibration|
|Beschreibung||Fix Color Calibration of HP CP 1515n Printer|
The objective of this project is to fix a HP LaserJet CP 1510 Series printer having color calibration issues.
Note that, if nothing else is mentioned, after each change I started calibration (at least, but usually only) twice.
Unfortunately, the short version worked only once. When I changed VR1 (see above), I also tightened the screws of the ITB. Hence there was a chance, that not the change of the trimmer led to success but the tightening of the screws. Hence, I changed back the trimmer to its original position and reassembled the printer. Then, as expected, the calibration failed again. Now I changed again the trimmer position as mentioned above and again reassembled the printer. Unfortunately, it did not work this time: Even after 3 calibrations the "L-lines" in the diagnostic page crossed each other.
Because of the above experience, I then supected a mechanical problem. Hence, I tightened the screws again. This time I used a special torque screwdriver and tightened all screws of the ITB module (which I could reach) with 1 Nm. Unfortunately, this did not help either.
My next attempt consisted of 4 things (I was quite in despair):
After reassembling everything again, it worked again.
Now I again wanted to know, which change was the successful one (i. e. was it the cleaning of the PCB or some mechanical change), I turned the trimmer back to its original position. Now the calibration failed again. But after carefully turning the trimmer again into its known-working position, calibation was successful again.
Finally, I did some sensitivity analysis of the calibation working or not for various trimmer positions. During this analysis, at some point it did not work again. I then only increased the spring stiffness (again) without changing anything (apart from the "good" VR1 position). Afterwards, it worked again.
Then I inspected the mechanism which tightens the belt a little bit more carefully. From the beginning on, I noticed two rather loose plastic parts near the springs, which function I could not identify. After having reassembled the springs I noticed that they have to do with the tightening mechanism. The two plastic parts are levers to relax and tighten the ITB. However, I did not found any information about this feature in any document - neither the printer manual nor the service manual! Additionally, this tightening mechanism can be accessed even if the printer is fully mounted - with only the front door open (TODO: pictures!). Hence, it may have been enough to relax and re-tighten the ITB after re-assembling the printer instead of having to increase the spring stiffness at all! The re-tightening might increase the fit of the ITB assembly inside the printer.
Hence the original problem seems to have 2 causes:
Finally, I did some sensitivity analysis of successful calibration to the positions of the 3 trimmers - starting from the now hopefully well-reproducible good position of VR1.
TODO: As it turned out, I obviouly initially hit the correct trimmer position of VR1 by chance: The trimmer position must be in a range of about +/- 5-10 degrees to be optimal, i. e. leading to a correct calibration!