17th September
1st Call 4 Service Ltd visited a HP 500 Designjet with error code 21:10
Customer had replaced carriage belt and had done a very good job, but after switching the printer back on they found the error code 21:10 which is a code for the ‘Service Station’ fault. The customer replaced the service station, but still had the 21:10 error!
Customer called 1st Call 4 Service who found the problem to be an Interconnect Cable has been trapped by the Service Station Holder (Right Hand Bracket,) the interconnect cable runs between the electronic module and the Interconnect PCA.
All you need to do to fix this issue, is to loosen the 4 screws on Service Station Holder (Right Hand Bracket) with service station still on printer, then softly work the interconnect cable loose of chassis and bracket, switch printer on to verify you have cleared the fault then tighten the 4 screws and re-test by powering printer back on again.
Fitted all covers back on to printer, then carried out some test prints to check printer for any other issues.
This issue of trapping the cable is so easy to do so if you attempt to replace belt please take care in this area!!
HP Designjet Repair Service And Maintenance 
Thanks for your post. This one got me too after I replaced the scanner belt. I didn’t see the pinch because of the routing of the interconnect cable. It is very easy to miss. Thanks again!!