Strange issue on this machine, so i will try to explain every from the beginning.

This all started with a L4-12 error about a month ago. when the tech went out he noticed there was also a c1-01 error logged. he tested the main charge cleaning mechanism and it worked fine,he then replaced the springs that hold the secondary transfer in place with the updated springs from a tech bulletin addressing this. He also performed a black pm as it was almost due. everything tested out fine.

5 days later it came back with a C4-20 error. the machine would still print with the error, but the customer would power cycle the machine to get rid of the error. it would come back within the hour. the tech went out and installed the mylar that goes around the contact of the primary transfer unit to prevent contamination. tested everything and closed the call. 2 days later and 5k prints later the error came back. when i got there i noticed that on some prints the print was blurred in the center of the page vertically, i inspected everything, updated the firmware from 4.5 to the 6.5 and tested 200 pages to see if the blur or the error code would come back. everything tested fine, closed the call. within the hour i got a call for c4-20 machine totally down.

when i got there the machine was in a hard error state and there was a jam at the primary transfer belt. the blur was back but this time half the page was fine(lead edge) and the middle of the page was clumps of toner. when looking at the transfer belt it looks like the page stops half way and the transfer belt keeps going, causing the "blur". During testing i found that color copies and prints will work all day. as soon as you make a black and white copy or print(internal prints as well) the paper stops at the primary transfer, smears in the middle and throws a c4-20. looking at the trouble log it also logs a f2-49 lsu thermistor error. LSU test pass, transfer test pass, did a dv disable and added toner to test tcd sensor, passes 50-22, 44-6, 44-26 and high voltage test. it will only fail if you print black and white except for (here is the kicker) the 64-5. the 64-5 color and black and white test pattern print fine with no issues????

I have replaced the drums, developer, PTC, transfer assembly, MC PWB, TC PWB, PCU PWB, drive assembly with new clutches and sensors.

I know this is long but i am reaching for the stars here, this series has given me so many issues i just want to blow em all up. anyone have any insight on this? thanks in advance