TM 1-1520-238-T-7
Change 3
11–311
11–76.
26 VAC EXCITATION XFMR 1 NO-GO AFT AVIONICS BAY –
11–76
APPEARS ON HOD (cont)
8. Check for 21 to 26 VAC between (A342):
J2–9 and J2–10.
Is voltage present?
YES
(ACB) Go to step 11.
NO
Replace isolation
transformer/filter assembly box
(TM 1-1520-238-23).
9. (ACA) Check for 115 VAC at P499–B7.
Is voltage present?
YES
Go to step 13.
NO
Go to step 10.
10. Check for open between P499–B7 and
(A402)J1–54.
Does open exist?
YES
Repair open wire.
Go to paragraph 11–23.
NO
Refer to TM 1-1520-238-T-6 to
troubleshoot circuit protection
system (ac essential bus 1 –
pilot station).
11. (ACB) Check for short between A708–69 and
ground.
Does short exist?
YES
Go to step 12.
NO
Go to step 15.
12. Detach P688. Check for short between P688–69
and P693–9.
Does short exist?
YES
Repair shorted wire between
P688–69 and P693–9.
Go to paragraph 11–23.
NO
Replace filter adapter
(TM 1-1520-238-23).
13. Check for 21 to 26 VAC between wire end
(A323)TB2–1–J and GS1–A.
Is voltage present?
YES
Go to step 17.
NO
Go to step 14.
14. Check for 115 VAC at (A323)TB2–1–C.
Is voltage present?
YES
Replace 26 VAC excitation
transformer (A323)T1
(TM 1-1520-238-23).
NO
Repair open wire.
Go to paragraph 11–23.
15. Check for short between P693–1 and ground.
Does short exist?
YES
Repair shorted wire between:
P693–3 and P445–A3,
J445–A3 and J234–1.
Go to paragraph 11–23.
NO
Go to step 16.
16. Check for short between P693–3 and ground.
Does short exist?
YES
Repair shorted wire between:
P693–3 and P445–A3,
J445–A3 and P413–A1.
Go to paragraph 11–23.
NO
(ACB) Go to step 19.
17. Attach wire to (A323)TB2–1–J. Detach P493
and wire from (A323): TB3–6–K and TB3–6–B.
Check for 21 to 26 VAC at P688–69.
Is voltage present?
YES
Go to step 20.
NO
Go to step 18.
18. Detach P499. Check for short between
P499–A13 and ground.
Does short exist?
YES
Repair shorted wire between
P499–A13 and P688–9.
Go to paragraph 11–23.
NO
Go to step 21.
