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  • Mark replied to the topic Fuel Quantity Test in Test Equipment
    You've got to move the fuel around while checking. Transferring fuel won't cut it as the values will be changing as fuel leaves the tank.
    Fluctuations are caused by bad probe terminal connections or a bad harness. These are seen in flight, rarely on the ground with a static plane.
    What type of aircraft???
    Jump on the wing if you can. Push-pull it with a tug.
    Get the fuel sloshing around somehow.
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  • Mark created a new forum post in Troubleshooting Tips
    DPCT's compare current loads on the major power feeder wires. They measure incoming amperage from their particular generator system to current draw of the user systems. They are most commonly seen on three phase power systems.

    The DPCT's output are monitored by either/both the Generator Control Units or the Bus Power Control Unit.As long as current loads closely match input  vs. output, the controlling contactor will remain engaged.

    If I high load is sensed on one leg vs. the other two..... it would indicate as possible short and the system would disconnect the contactor and take the generator offline. The same would be for a low/no load situation. This would indicate a possible open in the wires. The result is the same..... the generator is taken offline.

    Here are the APU Generator feeds in the electrical bay:

    A DPCT on the input wires to the APU Generator Contactor.
      
      
     
      
      
    Another one on the load side of the contactor.
      
      
     
      
      
     
      
       
    I encounterd a problem on a 757 in which the DPCT's did exactly what they were designed for.  rotate.aero/forum/ata-24-757electrical-p...-24-22-apu-generator
     
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  • Mark created a new forum post in Troubleshooting Tips
    We had a problem with a 767-200 Thrust Reverser Indication system in which the "T/R ISO Valve" light on the pedestal was illuminated for a few seconds after the reverser had fully stowed.
      
      
     
      
      
    767-200 thrust reversers use hydraulics instead of pneumaics (as found on newer engines) for T/R sleeve deployment and stow.

    Here is an example of thrust reverser operation. In this case, a pneumatic system installed on a 747. 
      
      
      
      
    With the 767 hydraulic T/R system, there is a lag time for the actuators to show stowed and for the pressure switch to signal that the pressure has dropped off. During that lag time, relay K10358 is relaxed providing a ground path for the light. It will energize when all the engine T/R functions have completed.

    The light being on along with the associated EICAS message during T/R transition would cause a nuisance warning for the crew during the landing phase of flight.

    Boeing solves this issue with a Time Delay Module inline with the ground path for the light.
      
      
     
      
      
    This module prevents current flow for a set time period. They can have different delay times. This one is for 7.5 seconds.

    If the module prevents current flow during the T/R sleeve transition for 7.5 seconds, no warnings will be seen by the crews.

    During troubleshooting, I jumpered the module in question. That was a useless attempt and totally defeated the purpose of the time delay module.
      
      
     
      
      
    I figured the best way to check one of these things was to put my meter "inline" with the system using the amperage function to measure the bulb current. This was done by removing K10358, and using pins 2 & 4.
      
      
     
      
      
      
      
    As can be seen, the module was "not"  stopping current flow for 7.5 seconds. As soon as I plugged in my lead, current was flowing and the light was on.

    A replacement module corrected the issue.
     
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  • To verify wire continuity for the specific power feeder terminals, any extra paths to ground had to be isolated from the wires being checked.

    From the drawing below, it can be noted some circuit breakers and a light bulb were connected to the feeder wires. The breakers were pulled and the light bulb removed. The APU contactor was not energized so nothing downstream from it would be considered connected.
      
      
     
      
      
     
      
      
     
      
      
     
      
     
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  • Mark created a new forum post in ATA 24 Electrical Power
    We had a problem similar to  this , where the APU generator was not coming online. Unlike the 757 issue which took a couple seconds to drop off, when the APU generator button was pushed on this aircraft....... instant disconnect.

    We had two fault codes on the BPCU (Bus Power Control Unit).
    Please excuse the shitty pictures.

    DP Trip
    DP is differential protection. The system senses a difference in amperage loads on the three wires. Either one is open (carrying no load) while the other two are good..... or one wire is shorted to ground, carrying a huge load compared to the others. This doesn't have to be just one wire either, two messed up wires will still cause a DP trip.
      
      
     
      
      
    Overlap Zone
      
      
     
      
      
    I really couldn't figure out the "Overlap Zone" from either the Fault Isolation Manual nor the Maintenance Manual. For the engine generators, there are current transformers labeled overlap, but I didn't see any for the APU.

    For this problem we found the phase wires installed incorrectly on the generator itself.
      
      
     
      
      
    To verify the correct wiring we took the three power leads off the generator and shot from the Generator Control Unit rack plug.
      
      
     
      
      
    To isolate the system to just the three power feeder wires, some ground service breakers and the APU Generator voltage feed to EICAS breaker had to be pulled. The red "Bus Hot" light had to be removed from its socket also. 

    I'm still wondering just how they were hooked up before we corrected them. The generator control unit just wants to see A-B-C as far as the phases go. This one could have been A-C-B or B-A-C??? 
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  • Black/White High Temp Tie-Cord

    BMS13-54HGDTIIIC1FC110/14WH
      
      
     
      
      
     
      
     
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  • Red and Green Tie-Cord 
      
      
     
      
      
     
      
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  • Clear high-temp heat shrink....
      
      
     
      
      
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  • Mark created a new forum post in ATA 26 Fire Protection
    Most engine fire detection systems come in two forms,  Systron-Donner or Kidde .

    CF6-80A and CF6-80C2 that use Systron fire detection systems have three equal resistance loop sensors. Each loop measures 4.5K Ohms. They are wired in a parallel circuit.

    In a functional system 1.5K Ohms should be read at the fire detection card pins 19 & 20.
      
      
     
      
      
    If 2.25K Ohms is read..... you've lost one loop. If 4.5K Ohms is read..... you've lost two.
      
      
     
      
      
    The "only" way to verify an open loop is to disconnect one (or both) wires from the loop terminals and measure resistance at the terminals (if the wires are connected..... you're reading the other loops and possibly the card).

    A loop is either good or bad. There is no halfway. 4.5K Ohms or open.

    If a bad loop has been isolated, throwing a decade box across the terminals should at least give you a valid test from the cockpit.
      
      
     
      
      
    Or..... just throw a 4.5K Ohm resistor across them.
      
      
     
      
     
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