The old “turn it on, and yank the power cord” is hardly the safest way to release the print head on an extremely expensive printer.
Here’s the correct way to do it (no dangerous moves required) :
Start in service mode*
select self-testing -> met Adjustment -> PG Adj
Press OK while Un Cap is displayed.
That releases the head.
When you are done, press OK again to have the machine restore the head to proper position.
* (hold down menu, paper-feeded,OK while powering on, and keep holding until you see the red x’s over the ink carts.)