tek 740 imaging unit error 22

[anewc2]

We have an imaging unit error 22. We swap it out for the old one -- at 3% but still creaking along -- and we can get things printed, for the time being. So I guess we need a new imaging unit. But the one we have is at 69%. Why is it suddenly dead? What else can we do to prevent this untimely demise?

I have the service manual. About error 22, the only non-obvious thing it says is to "Inspect the wiring harnesses leading in and out of the charger sensor board." A visual check reveals no discrepancy between the two imaging units. Other than that I am lost.

Amos