Service manual explaination is too general to offer addtional help.
"Two electrical parts have been replaced at the same time."
I was an HP Customer Engineer from 1995-2002. During this time, I serviced contract and warranty calls within the Northern Indiana area. When I left HP, I took my HP Designjet service experience and started my own business servicing out of contract plotters. Designjetpartsfast.com was launched in 2009. With over 20 years Designjet experience, I can help you resolve issues you are experiencing with your Designjet Printer.