(b)
Check continuity of harness lead between EGT circuit plug and terminal strip. On engine equipped with a junction box, perform continuity check on single wire leads only.
518 EGT Harness and Lead Schematic
Jun 20/89 Figure 502 (Sheet 1) BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 77-21-31 Page 503
G42799
EGT Harness and Lead Schematic 500
77-21-31 Page 504 Figure 502 (Sheet 2) BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Jun 20/89
1) Connect one ohmmeter terminal to pin I on EGT circuit plug and other ohmmeter terminal to alumel terminal (green lead) on terminal strip
NOTE: It may be necessary to use a long piece of wire (8 to 10 feet) to conduct these continuity checks.
2) Flex EGT harness lead gently where possible and observe ohmmeter needle. If needle fluctuates or does not show an indication, continuity does not exist. Replace EGT harness lead.
NOTE: Broken wires which come in contact intermittently due to flexing will cause needle to fluctuate. False intermittent indications will result if ohmmeter terminals are not in firm contact with clean terminals, or if ohmmeter terminals or leads are defective.
3) Connect one ohmmeter terminal to pins A through H successively on EGT circuit plug and other ohmmeter terminal to chromel terminal (white lead) on terminal strip.
4) Flex EGT harness lead gently where possible and observe ohmmeter needle. If needle fluctuates or does not show an indication, continuity does not exist. Replace EGT harness lead.
(2)
Test harness continuity at EGT circuit connector receptacle or junction box.
(a)
On engine with EGT electrical connector, connect one ohmmeter (sensitive) terminal to pin I and other ohmmeter terminal to pins A through H successively. On engine equipped with a junction box, connect one ohmmeter terminal to AL terminal and other ohmmeter terminal to terminals 1 through 8 of junction box successively (bus bar removed) (Fig. 502 and 503). On engines with boost circuit at junction box, remove terminal connector at terminals 1 and 6. Connect ohmmeter terminals to terminals 1 and 6. Connect one ohmmeter terminal to AL terminal and one ohmmeter terminal to terminals 2, 3, 4, 5, 7, and 8 of junction box successively.
(b)
Flex EGT harness lead gently where possible while performing continuity checks and observe ohmmeter needle. If needle fluctuates or does not show an indication, continuity does not exist.
(c)
If continuity does not exist through any one EGT probe, check for continuity across corresponding probe terminals (Fig. 503). 1) If continuity exists, replace EGT harness. 2) If continuity does not exist, replace EGT probe(s).
(3)
Test insulation resistance between conductors and ground.
500
May 01/00 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 77-21-31 Page 505
EGT Harness and Lead Schematic 518
77-21-31 Page 506 Figure 502 (Sheet 3) BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Oct 20/91
518 Exhaust Gas Temperature Harness Layout
Oct 20/91 Figure 503 (Sheet 1) 77-21-31
Page 506A
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
Exhaust Gas Temperature Harness Layout 518
77-21-31 Figure 503 (Sheet 2) Sep 20/82
Page 506B
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
WARNING: TO REDUCE POSSIBILITY OF IGNITING FUEL, DO NOT USE A MEGGER OR OTHER HIGH VOLTAGE OHMMETER.
(a)
Ensure that the thermocouple cable and leads are properly installed and connected.
NOTE: Insulation resistance values slightly below the limits set forth below will not result in a defective EGT system. It does, however, clearly indicate that the insulation is deteriorating and will result in eventual shorts or deficient EGT readings. Therefore, EGT system components with insulation resistance readings below the limits set forth require attention to restore the insulation resistance to acceptable values and prevent further deterioration and EGT system failure.
(b)
Check proper operation of ohmmeter (low voltage) by touching test terminals together and noting needle deflection to read zero ohms.
(c)
Place one ohmmeter probe in contact with harness steel wire braid and other ohmmeter probe to terminals A through H or terminals 1 through 8 on junction box (bus bar removed).
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