[Test-Equipment] HP8405A Vector Voltmeter Parts

[Arthur Shulman]

Hi folks,
I have the above unit with a dead 'B' channel. I have swapped the
replaceable probe boards and determined that the fault follows the
board. The diodes test OK, so the only remaining thing to replace is the
unmarked HP FET on the board.
Does anyone know what this part is, or, better yet, has anyone a good
replacement board they would be willing to sell?
Any advice, short of purchasing anothe unit, would be appreciated!
Arthur Shulman VE3ZV