Auto-Zone Control Systems Auto-Zone Plus Systems Installation & Operation (Version 03A) - Manual (Page 169)

Auto-Zone Plus Section 4
Start-Up and Troubleshooting 4-19
1.3.10 Checking Zone Controller and CV Unit Drivers
Diagram
Meter Set To Read DC Volts
T to SHLD
CV, CV-C
or Zone Controller
CV, CV-C
or Zone Controller
R to SHLD
+ -
T
R
SHLD
+
-
+2.4 VDC
to
+3.3 VDC
COMM
LOOP
T
SHLD
R
+ -
T
R
SHLD
+
-
+2.4 VDC
to
+3.3 VDC
COMM
LOOP
T
SHLD
R
Note: These tests assume that the controller being checked is powered up.
Overview
This check is intended to determine if the Comm Driver chip on a controller is damaged.
Damage typically occurs when the communications loop is exposed to excessive voltage, as
may occur during installation, due to wiring errors. The driver chips are socketed on all
boards to facilitate servicing. It is unusual for driver chips to fail during normal operation.
Almost all failures occur as a result of wiring related problems.
Measurements
Local Loop Acceptable Range
T – SHLD 2.4-to-3.3 Volts DC (Measured T-G and R-G Voltages should be within
0.1 VDC of each other)
R – SHLD 2.4-to-3.3 Volts DC (Measured T-G and R-G Voltages should be within
0.1 VDC of each other)
Note Minor variances may not indicate a problem if both tests indicate similar values.
Action
Condition Action
If voltages are outside the acceptable range
or T-G and R-G readings differ from each
other by more than 0.1 VDC The controller has a damaged Comm
Driver chip. Replace the driver chip. See
"1.3.11Comm Driver Chip Replacement”.