||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.
- Color calibration of a HP Color LaserJet 1510 Series Printer (e.g. CP 1515n) is not working correctly (see top left part of image)
- All attempts to fix the problem otherwise have failed:
- Update to latest firmware
- Repeated calibration (> 3 times)
- NVRAM reset
- Reset to Factory defaults from menu
- The following other attempts were not done:
- Replace the ITB assembly (cost reasons)
- Buy set of original HP toner (cost reasons)
- Print diagnostics page using the printer menu (for later comparison).
- Get the service manual (Google for "HP Color Laserjet CP1215 CP1515 CP1518 Service Manual")
- Follow the instructions for removing the Intermediate Transfer Belt (ITB)
- Turn the ITB assembly upside down
- Find the two small PCBs where the wires end
- Take a photo of the positions of all 3 trimmer (labelled VR1, VR1 and VR2 on the two PCBs)
- Find the trimmer labelled VR1 on the right of the two PCBs (the board with 2 trimmers on it). Example:
- Turn VR1 clockwise (for me, 90 degrees worked. However, the calibration seems to be quite sensitive to the exact position. Hence you have do some trial-and-error here. Example:
- Follow the instructions of the service manual for re-installing the ITB assembly
- Connect printer to power
- Start a color calibration
- Print diagnostics page and compare with diagnostics page before the fix
- Done (or try another trimmer position)
- If no trimmer position works, see long version
- This fix will certainly break warranty. Hence, only do it with printers being out of warranty!
- The fix proved to work for a single CP1515n printer. It may have to be modified for other instances.
- If changing VR1 on right PCB does not solve the problem, try the other trimmers (But always remember the original state!)
- When testing the effect of changing the trimmer, you only need to reassemble the following components
- The ITB itself
- The print-cartridge drawer stop
- The Print-cartridge drawer
- The left cover for your own safety, because the high voltage components are located beneath it
- But (as always) be careful not to touch any live parts when the printer is connected to power!
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):
- I temporarily dismounted the front top part of the ITB (see TODO) and remounted it afterwards without doing any real change.
- I dismounted the two coil springs which seem to tighten the belt and stretched them with two pairs of pliers - for the purpose of increasing the spring stiffness (in a very amateurish way)
- I again turned all 3 trimmers in the exact position where the calibration initially worked
- I dismounted the 2 PCBs and removed the plastic covers covering the component side and cleaned them (for details see below)
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. 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!