LCD does not work

[laszlo]

Hi,

I just finished building the first one of my two controllers.

Voltage checks were ok, but after populating the IC sockets and connecting the LCD and switching on, the LCD remains dark.

Everything else seems to be operational though because it appears on the network, the web page comes up, etc.

Apart from the LCD everything seems to be OK. It works the same way from USB and from the transformer.

I checked the voltages (the ones where I guessed DC from the label) on the LCD module and this is what I get:
VSS – VDD: 4.95V
VSS – V0: 4.95V
VSS – A: 4.95V
VSS – K: 4.95V

Any advice what else I should check?

Thanks

Laszlo

[Ray]

Check if you have soldered RLED (100 ohm) resistor correctly.

[laszlo]

Hi Ray,

Thanks for the advice. I have not fixed it yet, but I think I know what the problem is.

I have the 100ohm resistor as RLED, but there is nothing in D4. So, the backlight cathode is connected to Vo, but nothing pulls Vo toward Vss, so they happily float together close to Vdd.

I may have misunderstood something, but in light of the schematic, the assembly instructions may be misleading.

The 1.4u instructions say: (Oct 2012 PCB Update: solder RLED, a 100 ohm resistor located at the top of the PCB.)
The rest of the cell on the page is greyed out, which makes the impression that nothing should go into D4.
Looking at the component list, it does not say anything about RLED, but lists a 100ohm resistor as D4.
Also, there was no leftover on the bench when I finished.

I guess the easiest fix is to put a 1N4148 into D4. I will try that tomorrow (it is past midnight in AU).

Thanks

Laszlo

[Ray]

I see, I thought you have 1.4.2u (which does not have 1N4148 but a 5.1V zener diode instead).

Anyways, it looks like you have the 1.4u. Is your PCB showing July 2012 as the date or Oct 2012? D4 only appears on July 2012 PCB. I grayed that part of the instructions out because I assumed anyone who has bought the July 2012 batch would have finished building the circuit by now.

[laszlo]

Yes, the PCB is July 2012, so the kit is 1.4u. I had lots of weather dependent building/landscaping stuff to do before, so I could not get to assembling the controller before.

Anyway, I just soldered a 1N4148 into the D4 position and everything works perfectly.

Thank you very much for your help.

Laszlo

[Author]

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