HP Designjets drop detectors are sensors that look at the drops coming out of each cartridge and pass or fail that cartridge. In the photo at the left my finger is pointing to the drop detector of a 750c. There's only one problem with most of these old drop detectors...they get covered in gooey ink and no longer work. You have 3 choices when you start getting errors related to drop detectors:
1. Set PEN CHECKING (via your menu, usually under Device/Plotter Set Up) to OFF. You don't need it, you know if your cartridges are working better than the 1997 drop detector does!
2. Remove and try to clean the drop detector...be warned there is a small circuit board hidden in the drop detector's black plastic casing so you can't just flush it with running water. But you can open the casing with a small flat knife via the plastic seam. Once open you can pull the circuit board out and wipe down the sensors and rinse the black plastic casing to get all the old ink out. (See below for photos relating to this procedure.)
3. Replace the drop detector by buying a new or used one online...
NOTE: Both cleaning and replacing the drop detector require that you re-calibrate the drop detector...look it up in your service manual. If you can't find it, contact me and I'll help.
1. Set PEN CHECKING (via your menu, usually under Device/Plotter Set Up) to OFF. You don't need it, you know if your cartridges are working better than the 1997 drop detector does!
2. Remove and try to clean the drop detector...be warned there is a small circuit board hidden in the drop detector's black plastic casing so you can't just flush it with running water. But you can open the casing with a small flat knife via the plastic seam. Once open you can pull the circuit board out and wipe down the sensors and rinse the black plastic casing to get all the old ink out. (See below for photos relating to this procedure.)
3. Replace the drop detector by buying a new or used one online...
NOTE: Both cleaning and replacing the drop detector require that you re-calibrate the drop detector...look it up in your service manual. If you can't find it, contact me and I'll help.
The service station from a 750c.
Undo the four tiny screws on the top edge and remove the retangular black "frame" that hold the service station together.
Here's the drop detector. Lift it out...there was nothing but the frame holding it in place.
Slide a flat blade into the plastic box seam of the drop detector to force the two pieces apart.
See the drop detector circuit board? Now lift the cover off and then take out the circuit board...
The 3 pieces that make up the drop detector.
Circuit board with the round "eye" on the top right that needs to be cleaned off with a cotton tip and some alcohol...and the other piece that looks like a tiny lens (left upper) that also needs to be cleaned off.
The left side of the sensor goes into the clear plastic front box on this plastic housing (right side).