| had a copystar 5050 last week giving black copies and internal prints. thought it was the engine board due to improper volts from connector "yc7"-pin#4 when running maint. mode 100. (main charge on). we put an engine board in and downloaded current firmware. copier worked for a day and started the black copies/prints again. gutted copier and found nothing apparently wrong-- no signs of arcing, no burnt wires, nothing..after working with it for a good bit, i noticed that during the times when i was getting good copy/prints, i could run maint. mode 100 and all sounded good.. BUT- when i was getting black copies, and running maint. mode 100, i would here a high pitched squeel. replaced the drum ass'y(with main charge unit) and problem solved. turns out the main charge unit was arcing internally..good luck | 
Linear Mode
