With CRT/DID

CIRCUIT DESCRIPTION
The serial data line is redundant at most of the devices that it communicates with. While only one line need be connected to each device for that system to function, when making repairs both lines should be made operational. If when the ALDL cover is removed the system shuts down, a single open existed before, and a second open is being created by removing the ALDL cover.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.
1. This test and all subsequent tests are designed to subdivide the data line. This is necessary in order to pinpoint the location of an open in the data line. This is not the only way to pinpoint an open, but, in general, will most quickly lead to the open.