Lcd Backlight - Novatech 1730 Series Reference Manual

Novatech Controls 1730 Series Diagnostics Mode Reference Manual
If any of the lexan LEDs are not working then check the signal on the flexible cable between the display
PCB and the lexan. The lexan itself is unserviceable, so any failed LEDs would require the replacement
of the lexan label.

23. LCD Backlight

Overview: The backlight on the LCD display can be enabled and disabled from the MCU. This test can
check what state the backlight is in, and whether it is functioning properly.
Option Up/Down: toggle the backlight on/off
Enter: no operation
If the backlight is not working then the LCD module will need replacing. The LCD module itself can be
replaced individually. Alternatively the whole display circuit board with LCD module can be ordered as a
complete assembly allowing for simple swap-out replacement.
24. RS232 Port
Overview: This non-interactive test allows for simple automated testing of the RS-232 serial
communications on the transmitter. To test the RS-232 port place a jumper between terminal pins 18 &
19 – RS-232 Tx and RS-232 Rx.
Option Up/Down: no operation
Enter: no operation
The serial port continuously transmits a string of characters, while simultaneously listening for a
response. By placing a loop between the Tx and Rx terminals the device will continuously receive the
string of characters that it transmits therefore confirming that both transmit and receive are working.
If both transmit and receive are working the words 'Loopback ON' will appear on the display. If these
words do not appear when there is a short between terminals then there is a problem with the Tx or Rx
circuitry.
Before testing any of the serial port circuitry, first check the voltage test-points located adjacent to PS1
marked SGnd,+12,-12. On the newer boards there is also a +5 test point added. Confirm that each of
the test points measure the correct voltage with respect to SGnd.
Testing for serial port problems will require tracing the signal output from the MCU using an
oscilloscope. The testing itself is broken down into testing the Tx circuitry first, then if it can be seen
that this works, test the Rx circuitry second.
The first test should be to observe the Tx and Rx and 485 LEDs. During this test, the 485 LED should be
off. If the 485 LED is on then check the track between resistor R38 and the MCU pin P2_4.
If the Rx LED is on when the loopback jumper is OFF then there is a problem with either the logic chips
IC18, IC19, or the optocouple OP4. Using a DMM, check some of the states of the pins. If IC18_9 and
IC18_10 are high and IC18_8 is low then likely it is not IC18. If IC19_3 is high and IC19_4 is low then
replace OP4.
With the loopback jumper OFF the Tx LED should give a short flash every second and the Rx LED should
stay off. If the Tx LED is not flashing then this suggests that the signal from the MCU is not getting as far
as the LED. Use an oscilloscope to trace the signal through OP3 and IC10 to find the problem, also
confirming that the Tx LED is working and does not have twisted legs inside the standoff.
Document Revision 1.03 Page 14 of 16 Diagnostics Mode v1.08