Yellow not printing or copying

[Reeves]

Hi Techs am working on a Xerox Dc250 black Magenta and Cyan are coming out Okey except for Yellow its just coming out blank this r the following parts have tried but still yellow is not printing
1. Developer housing
2. Drum
3. Transfer belt
4. Ros(yellow and magenta)
5. PSHV S8C pwb
6. PSHV-S7C pwb

Have inspected contacts gear on yellow they are all Okey I swapped yellow and cyan developer housing yellow printed but cyan came out blank
Help what could be the problem

[xcopytech]

Have you replaced just transfer belt or transfer belt assy?

[Reeves]

Have you replaced just transfer belt or transfer belt assy?

Yes have replaced the transfer belt assy but still the same

[xcopytech]

Flat cable between ros and mcu pwb or mcu pwb