Mark

You hope the thing is there.
On this latest aircraft, our sheet-metal guy was able to replace the forward one without removing the whole detector/sensor/fan mount assembly.
A one hour change could of changed to a whole day affair. 

ELT's output two frequencies. 121.500MHz and 406.025MHz.

The 121.50 signal is just a tone. Rescue operators use a device to look at signal strength and direction to find the location of the ELT transmitter.

406.025MHz is a digital burst of data that reports encoded aircraft/owner information, a unique identifier number, and Latitude/Longitude position information.
A good explanation can be found here .

We usually try not to send data or tone out in to the open air during testing. Either a direct co-ax cable can be connected between the ELT antenna output or a shield can be placed around the antenna with a co-ax leading to the tester. Direct hookup is the preferred method.

This is not to say we can't just send signals out without shielding. The allotted time frame for testing in the USA is during the first five minutes after the top of the hour. We usually call the tower to inform them that a test will be conducted.
  
 

Those are internal relays.

Two lines, normally open.

Two line with diagonal, normally closed.

Abbreviations such as GCR, Generator Control Relay.

UV, Under Voltage.

OV, Over Voltage.

These are depictions to simplify the circuit. There doesn't have to be a physical relay. It could be an actual transistor that's doing the job. They could be logic circuits also.

 

Further explanation.....

The square opening at back of the operating blower is used for discharged air.

When a blower is running, its own flapper is being pushed back to let the air escape.

The non-running blower will have its flap pulled "in" because of the suction through the manifold.

We recently had a aircraft with a #1 blower failure (the #1 is the primary and is powered up first).
The blower failed which caused the system to use the #2.
The flapper on the back of the #1 was missing.
As the #2 was blowing, air entered the back of the #1 blower into the manifold.
No air was drawn through the detectors and the pressure switch was not being activated.
The system threw a EICAS message of "Cargo Det Air" because all smoke detection in that bay was inoperative.
  
Crappy image, but  it shows the location of missing flap for the #1 blower.
  
     
  
Replacement flapper.
  
     

 

We don't troubleshoot component internal workings.

If a system is failed and a replacement unit corrects the problem..... we're done.

Internal repairs are done at the shop level. Tests and certifications are required before the unit is returned to service.

Did you check the things I suggested earlier?
Wet bussing plug to tank harness connection.
Did you try swapping bussing plugs?

This is the adapter to check individual probes at the removed bussing unit at the wing spar.
  
     
 

Ref:  rotate.aero/forum/test-equipment/224-fuel-quantity-test
You need a PSD-60 or equivalent fuel quantity test unit. You need the appropriate break-out test cable. You need the test adapter to check individual probes at the bussing plug.

NEVER USE A CONVENTIONAL MEGGER FOR ANYTHING INSIDE THE TANK!!!

 

Please reference:  rotate.aero/forum/767-28fuel/738-fueling-bay-door-switch for more information about the switch itself.

When the fueling bay door is fully opened, a proximity switch activates the fueling bay and all associated fueling valves.
  
     
     


This switch is not an inductance device that is used for gear, gear door, and air/ground sensing. The fueling door switch is purely mechanical.
  
     
  

When a magnetic target is moved close, a mechanical switch is made inside the unit.

This type of switch is used in two places on the 767, the fueling door and the APU Inlet  door.