Are you using an allen wrench to adjust/position the locking cam? Play
with it to see what im referring to, if you haven't already. It needs to
be positioned far aft and with the near cam down at first. After install
you then rotate the allen wrench which deploys the aft cam and sucks it
up against the tray's slot.

Have you examined the pins on the back to ensure any are not
bent/misaligned (assuming you have a dsub connector on the back - this
is generic advice, not unit specific)

Is the tray slightly bowed, causing the cam to catch where it shouldnt?

av8tr wrote:
Just wondering if anyone has removed a King DME from their aircraft.
Ours was removed to satisfy Canadian regs when it was imported from
the US. The AME told us just to replace it after certification. I
noticed a locking cam at the front centre of the DME. Trouble is when
I insert it into the tray it does not seem to go into the tray the
entire way. I don't want to force it be I'm afraid I might damage the
terminal plug in the rear. If anyone has removed and replaced a unit
before your comments would be appreciated.

Thanx Jurgen