Mark

A schematic print would be nice.

You're dealing with older 737's if I remember correctly.

The interphone system on this aircraft would be considered analog.

On the 767, all auto-pilot actuators are the same part. There are nine total. 3 each for pitch, roll, and yaw.
  
  
On each servo there are line replaceable electrohydraulic servo valves and shutoff valves.
  
     
  
     
  
     
  
We recently had an aircraft with a center auto-pilot that was not engaging.  The MCDP checks showed a failed command circuit for the rudder (or directional) servo. The rudder servos are inside the vertical stabilizer.
  
     
     
  
When the valve was checked from the Center FCC, a reading of approx 1100Ω was seen.
  
     
     
  
You would think "I've got continuity so the valve is good", but that would be wrong.

There are actually two coils wired in parallel. 1100Ω is the resistance of "one" of the coils.

When two coils of basically the same value of 1000Ω are wired in parallel, total resistance is about half the value of one.
  
     
  
When the replacement valve was plugged in, the value read at the FCC rack dropped to about 500Ω.
  

       
  
It should be noted.... the servo (or shut-off) valves plug into the case of the actuator. If we had the same resistance reading with the replacement valve, we would most likely have a open wire internally "in" the actuator. That would suck as now the whole unit would require replacement.
  
     
     
 

Leach relay P/N BACR13CJ2 causing a cycling "FLAP/SLAT ELEC" warning on the lower EICAS display.
  
     
  
This is different from the posts above because this one has a 115 VAC coil. All previous intermittent relays were direct current.
  
  
This particular one was failed for about 90 seconds and energized around 10. (I wouldn't have caught it if I wasn't looking at the EICAS screens for another reason.)

When failed the message was in view.

I pulled the relay and checked for power (X1) and ground (X2). These inputs never dropped off. I then jumped the 115VAC and a separate hard ground to the removed relay. It dropped off within 10-15 seconds after power was applied.

A new relay fixed the problem.

In the schematic below, the EICAS computers do not want to see a ground on "F3" of the "D" plug. If a ground is present..... the warning will display.
K730 has 115 VAC available all the time. It's looking for a ground to energize. That ground comes from the Flap Slat Electronics Unit on pin "K13" of the "B' plug. If the FSEU is operational, it will provide that ground and there will be no warning present.
  
  

Old, but it still gives some good information.
Same system on 767.
  

  

I'll reach out to the poster to see if he can help you out.

Burndy pin removal/insertion tool.
  
     
  
P/N ATB-3062-2

The Stall Warning system on a 767 warns the crew of an impending stall by shaking the control column.

There are two stall warning systems. If they both sense the stall, a control yoke pusher (nudger on the 767) physically pushes the yoke forward.

A flight crew notification on the EICAS status page will show "WARN ELEX" if the stall warning system has a failure.
  
     
  
We normally see this when the IRS's are not aligned, as the stall system cards need valid IRS data.
We had an aircraft with this warning after the IRS's were up.

The left system was not testing. The test should give you a shaker. When we tested both systems at the same time, the left shaker would start working and we'd get a nudger (with hydraulics on).

In the forward accessory compartment we checked the wiring on the left shaker..... they fell right out with a slight tug. That would explain why the left shaker would start working with the right already on. Vibration from the right helped the left have continuity.
  
     
  
It might be explained in the FIM or Fault Isolation Manual, but the schematics give no hint that the card must see continuity through the shaker coil.

The schematic will show how the card provides a ground to activate the shaker. It doesn't show how continuity is monitored. I can only guess that the card wants to see 28VDC on pin 34. The coil is not "working" (or shaking), so the 28VDC is present on pin 34. (If the shaker was activated.... all the voltage would be dropped across the coil)
  
     
     
 

Most lower cargo compartments will have a heating system.

On the 767, hot engine bleed air is fed into a long tube running the length of the cargo compartment floor. The tube has holes to disperse the heated air.

A temperature switch controls a valve that either applies or stops the hot air flow.

The airline I work for has two aircraft that will allow cold pack air to go to the forward lower compartment. This is to keep the bay cold(er) while on the ground in hot airport environments.