29
Error Codes and Fault Finding
1. Display shows minus signs.
This tells us that there is no response to input data, either because....
a) There is no data, and the display has timed out
b) There is an error in the data wiring.
c) One or more of the menu settings may be wrong.
You can test for a) and b) with a simple data monitor which you can make
with 2 diodes and a resistor, as shown below.
The Green LED should be on for most of the time, and you should see the
red LED flicker as data is sent.
If the red LED is lit most of the time, with the green flickering, your wiring may
be transposed.
If neither LED is lit, check your data source to make sure it is configured to
transmit continuously, and check your connections to make sure the cabling
and connector terminals used are correct.
If the Green LED is on, but no flickering of the red is seen, check that the
data source has been set to transmit permanently. If the data source is
another London Electronics Display, make sure it has been set to mode C1
and that the enable terminal on the serial output connector is connected to
data common.
2. You can use your PC to generate and monitor serial data, with a free
program called RealTerm which you can download from
:-
http://sourceforge.net/projects/realterm/
This can be very useful in diagnosing communication problems.
------
------
------
------
------
1K
Terminal numbers on input
connector of display
RS232 RS422/485
3
4
2
3
Simple Data monitor.
2 x LEDs connected
back to back and a
resistor.
Green LED on
most of the time.
Red LED
flashes with
data.
Green Red
