Missing yellow color mpc2500

[Dis]

Stop the machine during printing a full yellow page / large format and see if the toner image looks ok on the drum - in this case it would have nothing to do with the transfer unit. The laser shutter issue may be a reason as well as other possible problems within the PCU (improper contact of the charge roller...).

support on this ways testing~~

[Apprentice]

Why not swap first the the drum portion of the yellow PCU unit with the other color to isolate the problem.

[jivedancer]

Broken cable bias terminal within the ITB unit causes issues with yellow transfer usually no yellow

[Sashko]

I agree with Zeldman.
First you must update the firmware for BICU and System/Copy!

I had same problem on this machine but with another colour - black and cyan.
I had checked all components (PCU's, laser diodes, laser unit, transfer belt etc).
Before replacing the BICU board I updated the firmware for it and... this solved problem!