Panasonic FP 7742 Copier

First it reads it is E3-22 Exhaust fan problem possibly.
Panasonic FP 7713 User Manual Panasonic FP 7713 User Manual

Here is the manual

E3-40 means there is a problem with the machine reading the black level density...this is not normally due to a faulty component but is normally due to to dirt inside the machine and possibly old/worn developer and /or drum in the machine. These are items that would have to be replaced by a service man.

the error would be E3-10. this occurs with a high voltage power leak on charge corona unit. either the corona wire is broken or the unit is dirty resulting in high voltage loss. clean or replace as neccesary

yep!
e3 means a machine error and it need a service technician to fix it.
furthermore may i ask what e3 code displays on the screen (you might see something like this e3 10 , e3 40 , e3 01 etc)
i can still help you if it is e3 10
:)

E3-50 is the malfunction of the transfer wire cleaner. The transfer wire assembly is under the drum. The transfer wire is on the right. The cleaner moves back and forth. If you feel comfortable taking it out, respond. There are fine metallic wires in each slot, so don't break them

means copy density sensor output detection. try turning power on and off, then look at the copy quality

panasonic dp-4520 copier. e4-02 error code

check out my site for free error codes:


http://checkitright.spruz.net/main.asp?page=dp&dis=592197

That could be a few things. Your corona wires might need replacing. Something with the middle transport section, where one of the corona assemblies is at, is not making contact properly. Or it could be the high voltage power supply.

E3-40 is a toner density sensor error. It's probably toner getting built up on the sensor. It's located under the drum. It will look like 2 little LED looking things on a little circuit board about 3-4 inches long and half an inch wide. You can blow it out with canned air.
If that doesn't work, then the sensor needs to be replaced.