How to fix a "Tooth Skipping" occurrence on VJ-1638UH

1. Load some media to prevent screws or E-rings fall down inside the printer.
2. Remove the power cord and position the carriage in the middle of the printing area. ( Maybe you have to turn the PG motor by hand to upper the carriage and turn the capping motor by hand to lower the capping station. Unlock the carriage bracket by your finger.)
3. Manually turn the PG motor gear to put the carriage somewhere in the middle high position but the small E-rings on the 2 black gears (the ones that are engaged with the white vertical gear plates) are reachable and can be removed.
   Use a small pin to price off the E-ring and a strong magnet nearby to catch the E-rings when they pop off of the other right gear.
   Turn the motor gear manually to the opposite direction to lower the carriage in this way that the gear shaft is turned a half a turn and the small shafts in the black gears are in a position that they could be removed. (pulled out). DON'T pull them out yet !
4. Put some plates (paper sheets, smart chip cards, credit cards) under the lamps on both sides to support the carriage. Measure the thickness of the plates. (for example 2mm)
   Now pull out the 2 little shafts with E-rings from the black gears. The carriage is resting on the lamps now. Slide the 2 black gears to the side so they are not engaged anymore with the white plastic vertical gear plates.
   Lift the carriage by hand and remove the plates on one side lamp and add some material until thickness is now approx. 1.5mm higher. (for example 3,5mm). Do the same on the other side lamp support plates.
5. Slide in the 2 black gears to be engaged with the white vertical gear plates again. Manually  move the carriage up or down a little bit so the wholes of the black gears are matching up with the wholes in the shaft and insert the small e-ring shafts again.
6. Turn the motor gear manually in the direction the carriage is moving up and the E-ring shafts are turned a half a turn. Now you can try to fix the E-rings again. Again it is recommended to put a strong magnet nearby to catch the E-rings in case they fall down. We don't want some E-rings falling behind the printheads or somewhere in the carriage.
   If it is impossible to fit the E-rings (or you have lost them) you can put a small metal wire in the grove and wrap it a few times so the shaft cannot fall out. So this wire wrap can just replace the E-ring.
7. Now you can start the printer in diag mode and perform the head gap adjustment procedure with the correct toolings. (see maintenance manual for details).
   Check as well the low head-height, as the high head-height.
   Also check if the capping-station is not damaged, as it may occur that some plastic may possibly break if the carriage was put under pressure because of the capping-station not properly being settled.
   
   All that is written is from our own experiences, so maybe some details are missing or some steps are not 100% correct. So be careful and use your own technical skills to get the job done. It is not always simple, but doable.

One last note, when starting this procedure above it's important that you have the correct adjustment-tools and jigs with you, in order to be table to verify and readjust the head-height low and high calibration. Please note that the head-height calibration is to be done, only after the tooth-skipping is properly mechanically resolved.  This is important because otherwise there is the risk of overcompensating with software, without fixing the root-cause first...  Generally the software-adjustment shouldn't be done again, if te gears are mechanically properly fitting again on their previous, original position (only in case the carriage was not replaced).