Service manual

Test 2-1: Closed
Channel
Resistance Test
This test verifies that all relay contacts meet the closed-channel resistance
specification for the multiplexer. When making the Closed Channel
Resistance Test, the path measured always includes: a tree relay, a channel
relay, and one or more protection resistors. This test uses the test fixture
(see Figure 2-1).
The Closed Channel resistance specification for each relay is 2
Ω. Since all
HI path measurements include both a channel relay and a tree relay, the
closed channel specification is set to 2
Ω to detect any failure. It is possible
that a channel resistance greater than 2
Ω is not a failure. Further
troubleshooting, as described in Chapter 4, is required to verify a true HI
path Closed Channel Resistance Test failure.
Measuring
Protection
Resistors
Since there are 100 Ω protection resistors (R38 through R43) in the relay
paths, measure the protection resistor values to begin this test. The values of
the protection resistors are then subtracted from the measured path
resistance to determine the relay contact resistance. To measure the
protection resistor values, set the Agilent 3458A DMM to 4-wire ohms,
autorange and measure each resistor value with the DMM (see Figure 2-2).
Record the measured values in Table 2-1.
Figure 2-2. Protection Resistor Measurement Connection
2-4 Verification Tests