Nautel V-10 repair

Not exactly sure how it happened, but one of our Nautel transmitters malfunctioned!  It is a pretty rare event, so I thought the exclamation point was needed.  One of the PA pallets went bad and the transmitter lost 1/2 a PA module.  Since the TPO for this particular station is 7 KW, they remained on the air at full power.  In the interest of staying on top of things, we fixed it anyway.

Diagnostics were simple:

  • Fault lights on front of transmitter observed
  • Press status button to find out faults, which were Module D failed
  • To to module sub-menu, find Module D and discover Q1 disabled, Q3 shutdown.
  • Problem is with Q3, order new pallet from manufacture

Upon removing module, I did not see the damage at first:

Nautel V series FM transmitter PA module
Nautel V series FM transmitter PA module

It is board A3, which for this particular flavor transmitter is a Nautel Part number NAPA16-B. Once I replaced the defective module with a new one, I discovered what looks like a symptom of the greater problem:

Nautel NAPA16-B defective board
Nautel NAPA16-B defective board

Over to the in the left-middle-lower section of the board, R10 and R8 are burned open. These are surface mount 2 watt, 20 ohm resistors.  A glance at the schematic shows that these are part of the bias supply.  A quick set of measurements with a DVM shows that Q1 seems to be intact and not shorted.  Interesting…

The question is: Is it worth trying to fix this board or should I just trash it an buy a new spare?

Update: Schematic diagram as requested:

Nautel NAPA16-A schematic
Nautel NAPA16-A schematic