Backlight repair on MD-HMI?

[Joel Moore]

Is there anything I can try to do myself to troubleshoot the backlight on our MD-HMI?  This is the first time I've ever hooked it up but I'm pretty certain I've done it right.  I've got the 150 ohm 5W resistor in series with the 24 volt power and connected to the + terminal.  Then the other end of the power supply is tied to the - terminal.  But no backlight.

The only thing that I can think of that might have caused a failure is that I accidentally left the power supply on when I connected it to the terminal blocks which led to an audible spark.  I'm not even sure if something like this is damaging to a circuit but I figured I should mention it.

I'd like to try to see if I can repair it myself since we don't really have time to send the module back before it ships.  We can live without the backlight but it'd be nice to get it working.

[support]

If for an reason the 24V and 0V are applied directly to the LED backlight the backlight array of LED will be damaged.

Perhaps buying a new HMI to replace the existing one and send the damaged one back to us for repair may be the quickest solution.

To replace the LCD, you need to remove the LCD module from the HMI by desoldering the 16 header pin and replace it with a new LCD.

Alternatively, if you disassemble the LCD module, you can retrieve the light box unit in the LCD which is an independent unit that can be taken out of the LCD module assembly and replace with a new one. However, you will need to align the contact between the glass and the PCB properly otherwise there will be display problem (such as missing segment).