BP-70C31 missing Black image

[westoneking]

Have a machine that produces no black whatsoever. I replaced the LSU and the problem persisted. I had another machine to mess with so I took the old LSU and put it in that machine and it produced a black image no problem.

I cleaned the FFC to the LSU, I swapped the transfer unit out, swapped the drums around.

I'm thinking HVPS? No charge to the K drum unit. Only other thing I can think is the LVPS isn't giving the LSU enough Juice for the black laser.

What are your thoughts?

[ihatefinishers13]

Had a 5071 that would NOT print the black image. Ended up being the MFP-SCN PWB; it wasn't telling the LSU to write the black image. Tech support had me wrap a piece of ELECTRICAL tape over the charge grid and run ONE print, which should produce a thick black line just where the tape was. Tricky to swap that board to test, with the way the eeprom is now, but, that's what worked for me.