JD5420 Will P/up a JD280 disc, but won't let down. HELP

[deanfitz]

This is a 12' wide hydraulic disc, the tractor will pick it up, but will not release the pressure to let back down. Have tried everything from changing tips on hoses, bringing cylinders to shop, and changing the female coupler (black side) on the tractor. Does anyone have any idea's?

DISC IS A 12.5' WIDE JOHN DEERE 210, PULL TYPE W/ 2 CYLINDERS WITH FRONT & REAR HOSES TO CYLINDERS

 

[Tx Jim]

I've need heard of a JD 280 disk nor does one show up in JDparts.com. If it has a transport lock have you disconnected it when plow is in raised position??