Before some days a printer (Canon ip 4200) was brought to me. The printer was displaying error 6000 and the orange and green LED’s were blinking in 3 cycles. Service manual suggests that this is line feed error and parts which are likely to be faulty are timing sensor unit, timing slit disk film, feed roller assembly, platen unit, logic board assembly and paper feed motor. It was a vain attempt to check all these parts. Everything was looking to be fine but the printer was not functioning. This was strange because error 6000 is not rare in Canon inkjet printers. I solved it many times before. Spending a lot time brought me the success. The logic board assembly wiring was damaged. A wire of flexible white harness had gone open. I replaced it with a new one and printer was functioning properly. But normally this does not happen. Normally a bit of paper jammed in the feed rollers or a faulty LF sensor may result in displaying error 6000.