Category Archives: AircraftTroubleshooting

F900EX Generator traumas

Current troubleshooting: engines running:

  1.  Check for Bleed leak blowing on GCU.  BE very carefull if you elect to run the AI on the ground.  !!!!!!APU BLEED OFF!!!!!!, slats extended.    20 seconds ground test max. leave the slats out to cool.
  2.  Test “E” ground quality.  Fluke on volts.  Black lead to airframe ground, red lead to GCU Black test point.  Very small voltage~ .1v.  less is better
  3. Volt drop on line contractor.  Fluke meter on volts.  Red lead on upper contactor, bottom big bolt, black lead on same contactor, upper big bolt. Very small voltage~ .1v.  less is better.
  4. Ripple test.  use fluke MIN/MAX.

Run each test with only 1 gen online, 50 to 100 amps load, try to hold conditions quite similar for each test.

some other thoughts:
look at big E terminal, small 20awg terminal.

double check each  GCU voltage. Is it stable at 28.5? is it stable with load? is it stable with RPM change?

select cockpit red switch to off.  Is the voltage of a running generator, cockpit switch selected off,  .7v to 1.0v at idle? this checks the quality of the permanent magnets inside the Generator.

ASSURE that NO ENGINE GENERATOR  has a cooling fan installed. (possibly a borescope through the black sooty outlet.) or it mat be necessary to unbolt the cooling exhaust.

Initial problem definition:

#3 Gen Light occasionally, Much troubleshooting. Gen 3 amps tend toward zero. #1 seems to “take the load”



#3 gen troubleshooting, #1, #3 gen shunts…..?Removed?

Detailed summary of troubleshooting:


Old Auxilec presentation:




Westwind pressurization problem











The valve opens correctly with shop air applied, and the controller  disconnected, and slight vacuum applied to control circuit





Front valve will open when control i connected straight to the pneumatic relay.




Ground prepress seems to work correctly





Aircraft pressurizes hard on the ground, straight to 3 psi at idle.  Fwd valve will not open via the controller.


Turns out the limit valve was failed.  It had opened because the pilots got the cabin to 17,000 feet.  Then the brass seat fell out of place.  Then valve leaked from then on .





Removed failed altitude limit valve PN 102466-1  SN 88-2322.  Installed serviceable valve received on form.   PN 102466-1   SN 17-1898






Removed failed anti-ice pressure reducing valve PN 38E59-1D  SN 2907 -U. Installed Ovrrhauled valve recieved on AVITECH W.O. 1021932 PN 38E59-1D  SN RF3502.