[TenTec] no voltage to 1.8 filter?

[tlogan7 at cox.net]

Hi folks -
  I've determined that the 1.8 slot on my PTB board has no voltage coming
through  the three pin connector 41 on the rear left corner of the board.
When the 250 and 500Hz filters are engaged voltage will run through their
respective pin on the connector - but when I turn on the 1.8 I do not get
any voltage.
  I'm a total electronics nimno - but as far as I can tell the only
components on this board are either chokes, toroids with binocular type
cores, one normal toroid and three pots. So that must mean that the
connector at 41 runs to diodes that I'm guessing are in the jungle on the
back of the front panel - something I'm not sure I want to mess with.
  Based on this info does anybody have any additional light they can shed on
my 1.8 slot? It appears that it just plain does not get switched on even
though the panel light turns on . Thanks for any help.
73/Tim NZ7C