ATA 24 Electrical Power
1 - IDG & CSD oil servicing. 737-ALL
2 - Complete circuit-breaker list for in your pocket. 737-6/7/8/900
3 - Interactive training and cb module. (needs MS-Access to play) 737-6/7/8/900
4 - 737-300 electrical schematic powerpoint presentation. 737-3/4/500
5 - 737NG electrical power sources overview. 737-6/7/8/900
6 - IDG drainplug cracks due to overtorque. 737-6/7/8/900
7 - Engine Generator drops off line, when the other Gen is taken off line. 737-6/7/8/900
8 - APU Generator will not come on line. 737-6/7/8/900
9 - #1 Transfer Bus off light on. 737-6/7/8/900
10- #1 Transfer bus drops off line when APU starter disengages. 737-6/7/8/900
11 - Cockpit DC amp meter will not indicate load when selected to bat position. 737-3/4/500
12 - During Standby power test circuit breakers pop and voltmeter is high. 737-3/4/500
13 - When #2 engine is shut down the "Rt Transfer Bus" drops off line. 737-3/4/500
14 - CSD temperture goes off scale in both normal or rise. 737-3/4/500
15 - Transformer Rectifier #3 shows voltage but no amps with aircraft power on. 737-3/4/500
16 - When eng #1 is shutdown, #1 "TRANSFER BUS OFF" light comes on and power is lost to the Bus. 737-3/4/500
17 -
Aircraft will not accept ground power, Hot Battery bus circuit breaker pops
behind Captains seat when starting APU.
737-3/4/500
 |
|
1-
IDG & CSD oil servicing.
737-ALL
We still make many errors with "servicing" these things. Thus Sundstrand has made the arrow glass of the IDG better. Philosophy is that, irrespective of the temperature, the CSD/IDG always must be able to be serviced. At the CSD there is a rule effective that is not well stated in the manual! It can never filled above the middle of the band. Differently, it can never be drained when the level comes under the middle of the band. At normal operating temperature, after cooling, the oil quantity will never come under the band. Differently, at warming up to operating temperature the quantity will never come above the band. If the oil quantity comes outside the band damage to the CSD/IDG will occure. (It has occured that an engine could not be started because of a overfilled CSD.> OIL LOCK) .
Text & pictures provided by R. Meijer. See the illustrations for better explanation:
>> 737-1/2/3/4/500:
>>737-6/7/8/900
6 - IDG
drainplug cracks due to overtorque. 737-6/7/8/900
When you change the oil of the IDG, check the IDG drainplug for cracks. It often happens that the plug is installed with a too high torquevalue, causing it to crack or even break apart. The plug is not that strong and made of aluminum. It might cause a small oil leak making the IDG looking 'wet' without finding a clear source of the leak. The torque value is about 65 lbs/inch iaw amm 12-13-21. See pictures of a cracked drainplug. The p/n = MS9954-05
7
-
Engine Generator drops off line, when the other Gen is taken off line. 737-6/7/8/900
Possible Fix: Replace the IDG that drops off line when the
other one is taken off line.
Tip: It is probable that the GCU will only log a BTB fault, and not a IDG fault.
The generator will not trip if the Bus XFR switch is set to "OFF" position.
Reason: The normal AMP load of a engine generator while it is on-line is 35-40
amps, when the other generator is selected off line the remaining generator's
load goes up to 75-80 amps. A weak IDG will not be able to handle the increased
load required when the BUS transfer Kicks in.
Applicable Reference: AMM 24-11-11
Thanks to Tom S. for his input !
8 -
APU Generator will
not come on line. 737-6/7/8/900
Possible fix: If the APU GCU or the Starter Generator are no
help, APU remote fire switch (S16) located in the Rt main wheel well.
Tip: The contacts for the APU generator on the S16 are 1 and 2.
Reason: The S16 has a few different set of contacts, so it is possible for the
set going to the APU GCU to be open not allowing the APU to be put on line, but
the other set to be closed so the APU will still run. Reference: SSM
24-22-31, 26-21-11, 49-62-01, WDM 24-22-31.
Thanks to Tom S. for his input !
9 -
#1 Transfer Bus off light
on. 737-6/7/8/900
Possible fix: APU GCU
Tip: In the main E&E look at the #1 GCU (in this case we had a BTB Fault light
illuminated). Start the #1 engine and see if the generator will come on line and
extinguish the Transfer Bus off light. Then when placing the aircraft back on
APU bus 1 power, look to see if the APU bus 2 stays on line.
Explanation: This problem seems to come up at 5 minutes to push when the APU is
started, or is noticed then when the crew is doing their flow.
Applicable Reference: FIM 24-21 task 810, 24-41 task 801
Thanks to Tom S. for his input !
10-
#1 Transfer bus drops off line when APU starter disengages. 737-6/7/8/900
Possible fix: APU GCU.
Tip: #1 Transfer bus drops line when APU starter disengages, APU GEN AVAIL light
comes on but APU would not power the Aircraft. After APU was shutdown, the Bus
power control unit could not be reset until the aircraft power was shutoff and
the power cord was removed from the aircraft.
Reason: Whatever was wrong with the GCU it was doing a number on the Bus power
control unit (G-15), and it could not be reset until all power was removed from
the aircraft. This condition got worse the longer we worked on the aircraft, and
before we reset the BPCU we could only get Ground service on the aircraft.
Reference: SSM 24-23-21, 24-22-31
Thanks to Tom S. for his input !
11 -
Cockpit DC amp meter will not indicate load when selected to bat position. 737-3/4/500
Discrepancy: Cockpit
DC amp meter will not indicate load when selected to battery position. All other
positions indicate normal.
Possible fix: Replace broken terminal end for load meter shunt wire, located
inside battery connector.
Tip: You must remove power and disconnect battery connector and separate halves
of connector to install a new teminal end for the shunt wire.
Reason: a 22 gauge wire, connected to the negative lug inside the battery
connector supplies current to load meter shunt which in turn provides battery
load amps indication to DC amp meter, on the P-5 panel when selected to BATT
position.
Thanks to Tom S. for his input !
12 -
During Standby power test circuit breakers pop and voltmeter is high. 737-3/4/500
Discrepancy: During Standby power test circuit breakers pop and voltmeter is
high.
Possible fix: Static inverter.
Tip: You can look at the static inverter output voltage on the P-5 panel.
Reason: if the output voltage of the static inverter is high the amps will be
high also and will pop the circuit breakers. Hopefully it does not damage
anything.
Applicable reference: AMM 24-54-00
Thanks to Tom S. for his input !
13 -
When #2
engine is shut down the "Rt Transfer Bus" drops off line. 737-3/4/500
Discrepancy: When #2
engine is shut down the "Rt Transfer Bus" drops off line.
Possible fix: R355 Bat Bus relay, R1 Bat Bus relay Auto.
Tip: Check to see if the "Transfer Bus" light comes on when only the battery
power is on, attempt to put both APU bus's on line #1 first then #2. If only #1
APU bus comes on line. This could be an indication of no power to the 28V DC BAT
BUS. Also if the APU surge valve is open on the ground, that could be another
indication of no power to the 28V DC BAT BUS.
Place the Standby power switch to BAT and try using the sequence above to place
the #2 APU BUS online. If it works correctly that is a indication of a faulty
R355 or R1 relay.
With no power on the aircraft, VERY SLOWLY move the Battery switch to on. The R1
relay closes first giving you the two amber "TRANSFER BUS" lights and the
standby bus comes on. Continue moving the battery switch to on, next both "BUS
OFF" and "GEN BUS OFF" lights come on, and standby power goes off, this is a
indication that the R355 has closed.
Reason/Explanation: When Battery is switched on the 28V DC BAT BUS recieves
power from the HOT BAT BUS through the R1 and R355 (SSM 24-30-00). Both
"TRANSFER BUS OFF" lights are powered by the 28V DC BAT BUS (SSM 24-50-02). By
putting the standby power switch to BAT the hot battery bus is supplied to the
28V DC BAT BUS through the R326 relay (SSM 24-30-00).
The reason #2 will not go online if the #1 is already online is the APU
Generator control system thinks the aircraft is in the air and will only let one
APU bus online at a time. The Air/Ground system gets its power from the 28V DC
BAT BUS, without this power R281 can not go to ground mode thus preventing R38
from going to ground mode. If R38 is properly set to ground it bypasses both
C890 and C889 (APU GEN breaker) trip/close logic contacts) so it will let both
APU bus's to come on line (SSM 32-30-00).
Applicable Reference: SSM 24-30-00, 24-20-03, 32-31-00
Thanks to Tom S. for his input !
14 -
CSD temperture
goes off scale in both normal or rise. 737-3/4/500
Discrepancy: CSD temperture goes off
scale in both normal or rise.
Possible fix: CSD wiring harness
Tip: The CSD harness will get shorted or the connector pins will short together.
You can take the connector off and look at the pins, sometimes the insulation
breaks dowm and they will become visually displaced. Thanks to Tom S. for his input !
15 -
Transformer Rectifier #3 shows voltage but no amps with aircraft power on. 737-3/4/500
Discrepancy: Transformer Rectifier #3 shows voltage but no
amps with aircraft power on.
Possible Fix: R1, R2, or R326 Relay, C145 or C20 circuit breaker.
Tip: Check the C145 "Bat Bus Cont Auto" circuit breaker on the P6-5 for power
(located just below GCU's)if no power is there go back to the C20 "Bat bus"
breaker.
If power is available at the C145 on the load side, you can go to the R1 relay
and verify power and ground is available to the relay and it is closing. R1 is
in the lowest P6 panel.
If that relay appears to be operating go on to the next relay R326, and verify
power is making it to the Bat Bus,
Reason/Explanation: TR3 powers the Bat Bus during normal operation if this relay
network is bad the TR can be producing power but that power would not make it to
the Bat Bus.
Applicable Reference: SSM 24-30-00, WDM 24-32-01, 24-31-11
Thanks to Tom S. for his input !
16 -
When eng #1 is shutdown, #1 "TRANSFER BUS OFF" light comes on and power is lost
to the Bus. 737-3/4/500
Discrepancy: When #1 engine is shutdown, #1 "TRANSFER BUS
OFF" light comes on and power is lost to the Bus
Possible Fix:
R3 relay, # 1 GCU, R349 relay, C465 circuit breaker, P5-4 AC System generator
and APU panel, R350 relay, #2 GCU
Tip:
To verify system operation perform AMM 24-21-00-735-001, paragraph "R. Test of
the Control Circuits for the Engine Generators". This will allow you to identify
what the system malfunction is.
If both #1 and #2 Transfer Bus's are not working per this mm ops check. You
should verify 28VDC Switched Hot Bat Bus is present by checking that Circuit
Breaker C169 Switched Hot Bat Bus is closed, located on P18-5 cb panel (down low
behind the captains seat). If this circuit breaker is in, pull it, it should
shut off a bunch of stuff in the flight deck. ( You will hear the effect). per
SSM 24-30-00 if you do not hear the effect trouble shoot the source of the power
back towards the battery from C169. If you hear a diffence check for the 28 VDC
making it to the Transfer bus control circuit through R41, and the C4 circuit
breaker (per SSM 24-20-01) or C5 circuit breaker (per SSM 24-20-02)
If the discrepancy is only with the #1 Transfer bus not being powered when #1
Gen bus or #1 APU bus is powered off or lost. Go to R3 relay contact Y2 (located
in P6-4 circuit breaker panel) verify 28VDC is present and ground is present
when the #1 Gen bus/#1 APU bus is lost. per SSM 24-50-02
If power and ground are present on contact Y2 and Y1, of the R3 relay you most
likely have a bad R3 relay. NOTE THE R3 RELAY IS INSTALLED WITH THE CONTACT
NUMBERS UPSIDE DOWN WHEN YOU LOOK AT IT.
If no power is present at Y2 of R3 you can split the circuit by going to C465
circuit breaker and looking for 28Vdc.
If power is present at C465 follow it back accross P5-4 panel, and through R349
pins B2 and B3, then to #1 GCU pins A45 and B36. It usually faster to try
replacing these components rather t hen attempt to verify power at pins.
If no power is present at C465, follow it back through R350 relay contact A1 and
A2 then to #2 GCU pin A45. This circuit continues back to SSM 24-20-01.
Reason/Explanation:
If power from generator 1 is lost, GB1 will open and the coil of relay R349 will
de-energize. The circuit to normal coil of transfer relay 1 will open and the
circuit to the alternate coil will close. If generator 2 is still supplying
power to gen bus 2, the alternate coil of transfer relay 1 will energize,
connecting transfer bus 1 to gen bus 2. A 0.25-second time delay occurs before
the alternate coil energizes. This prevents bus transfer during normal power
source transfer. The sequence of transfer bus control for other power source
combinations is similar
The #1 Transfer bus is picked up by the other #2 Gen bus or #2 APU bus when
power is lost to the #1 Gen or APU bus. This Automatic power transfer in
performed by the R3 Relay, the control voltage comes through a network of relays
and switch's to make that happen. The 28Vdc control power comes from the
Switched Hot Bat Bus to make this happen.
Applicable Reference:
AMM 24-51-00-001, 24-21-00/101, SSM 24-30-00, 24-50-02, 24-20-01, WDM 24-00-01,
24-56-01,24-24-01, 91-03-24
Thanks to Tom S. for his input !
17 -
Aircraft will not accept ground power, Hot Battery bus circuit breaker pops
behind Captains seat when starting APU. 737-3/4/500
Discrepancy:
Aircraft will not accept ground power, Hot Battery bus circuit breaker pops
behind Captains seat when starting APU
Possible Fix:
Repair bad ground for aircraft battery. GD3252-DC
Tip:
With no power on aircraft, close battery switch, if you do not get the normal
battery powered lights and systems.
Check the P18-5 panel behind the captains seat for the Hot Battery bus circuit
breaker open. If it is open, close this circuit breaker and attempt to put on
the battery switch again. Even if it comes on. You should go directly to the
battery and remove the connection and verify a good ground at the plug. It is
required to be .001 ohms per the WDM 24-31-21. In this scenario you could put on
ground service then apply aircraft power and it would come on. This is because
you are back powering the Hot battery bus then holding it on with DC power that
is converted from AC.
Reason/Explanation:
A bad ground will have intermittent problems with different systems. It will
cause the Hot battery bus breaker on the P18-5 panel (C22) to open during APU
starts, it will cause problems with applying power. It could cause the Gen BUS
off light not to illuminate. It will make it appear as though the Battery is
dead. All these could be indications that the Ground for the battery is bad.
Applicable Reference:
WDM 24-31-21, 24-56-01 DWG #69-78615-3
Thanks to Tom S. for his input !