JCB Backhoe Powershift Transmission Problem?

I Have A JCB Backhoe 2003 model, which blows the fuse each time we select 2nd gear forward. We have replaced the gear selector assembly on the steering coloumn and one solenoid on the transmission but still the same. The auto electrician now says we should change another solenoid , but they dont sell them individually so we have to replace the whole control box and all solenoids ???? [ the previous solenoid replaced was 2nd hand and I can not find any more in Australia].The machine serial no:0938774
Hope you can help?
Peter Hayes.