EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
27-09-00
ALL ú ú 03 Page 4 ú Sep 20/98
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL
(2)
A total of six SCMs control the twelve spoilers. Each SCM controls a symmetrical spoiler pair, one on the left wing and one on the right wing. The spoilers are deployed during flight or landing to reduce lift and increase drag. Refer to 27-61-00 for more spoiler information.
(3)
The newer model SCMs have a BITE display on the front panel and will be referred to as the -200 series SCMs. The older model SCMs have faultballs and will be referred to as the -100 series SCMs. The -200 and -100 series SCMs are interchangeable and can be installed in a mixed configuration in any of the six SCM shelf positions.
(4)
The -200 series SCMs have an expanded capacity for fault detection and can isolate the fault to the possible defective component. The BITE display shows a list of the existing faults at its shelf position, and can show the fault history and the SCM position during the fault. When a -200 series SCM is available, it will provide the fastest and best fault isolation for spoiler system troubleshooting.
(5)
For an all -100 series SCM configuration, the most effective maintenance occurs when there are -117 and -118 SCMs installed at shelf positions 1R and 2R. This is because there are two types of the older -100 series SCMs: the -112/-114 SCMs, and the -117/-118 SCMs. The -117 and -118 SCMs have an improved ground speedbrake delay circuit which reduces the risk of a nuisance fault if a transient signal occurs in the air/ground system.
(6)
For an airplane that has the -100 and -200 series SCMs installed, the most effective maintenance usually occurs when you have at least one -200 series SCM installed on each shelf. The best location for the two -200 series SCMs are at the 1R and 3L shelf positions, preferably with a -117 or -118 SCM installed at shelf position 2R. If only one -200 series SCM is available, install it at 1R. If an intermittent problem occurs at a given shelf location, or when it is necessary to replace an SCM during the fault isolation procedure, a -200 series SCM is recommended for installation there.
(a)
When you use a -200 series SCM for troubleshooting an intermittent problem, it must be installed in the correct shelf location at the time the fault occurs for it to make a record in fault history. Use the fault monitor data below and the existing pilot reports to determine the best shelf location to install the -200 series SCM. Keep the -200 series SCM installed during subsequent airplane flights to let the SCM make a record of the intermittent fault. If the fault occurs again but is not recorded, move the -200 series SCM to a different shelf position and monitor the subsequent flights.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
27-09-00
ALL ú ú 01 Page 5 ú Jan 28/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL
(7)
One -200 series SCM, installed in any shelf location, will monitor these inputs:
(a)
The two actuators controlled by the SCM.
(b)
The three control wheel transducer inputs (Captain's or First Officer's) for the shelf with this SCM installed.
(c)
The three speedbrake lever transducer inputs (one of each of the three dual LVDTs) for the shelf with this SCM installed.
(d)
The PSM VALID signals from the two power supply modules (PSM) which supply power to the shelf with this SCM installed.
(e)
The three 26v ac signals from the PSMs which supply power to the shelf with this SCM installed.
(f)
The three air/ground signals that come to the SCM.
NOTE: There are four relays which supply inputs to the spoiler
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