Ambika LCD Freakout

I messed up my Ambika MOBO by initially putting the LCD on the bottom of the PCB instead of on top.
I ruined the LCD removing it.

The Ambika works beautifully, and while I waited for the replacement lcd I named it Blindika and followed the manual and enjoyed playing it without a screen.

I ordered a 3.3v 40x2 lcd from BuyDisplay and then realized that I needed a 5v so I contacted them and explained.

1) They were merciful and told me to keep the 3.3v when it arrived, but they would send a 5v out to me asap.

2) I got another message from them advising me on how to convert the 3.3v lcd to a 5v

Seemed simple:
a) remove R11 completely
b) replace R12-R13 with a 51R SMD resistor
I was excited to try this, as I seem to get a thrill from working with SMD components, so I did it and it went very well.

Naturally I couldn’t resist trying it out on the Ambika. So I replaced the header (on the top this time) with three jumpers made from wrap wire to make sure that the solder sucker messed up pads were connected nicely to the pins, and put it in place.

At first it seemed like success. All systems go.

After 10-15 minutes the LCD kind of freaks out, and then becomes a single flashing cursor.
a) Quickly reboot, and it’s the same.
b) Power off for 10-15 minutes and it seems fine for 10-15 minutes (repeat)

So what’s wrong, and where shall I look to fix this?

  1. Do I surrender, and remove the LCD (again) and add the 5v LCD and hope to the stars I don’t ruin the Mother Board in new and exciting ways?

2) Is this possibly a pre lcd resistor issue? Right now there is a 47R resistor in place.
Could this freakout be from too much voltage? Not enough voltage?
Wouldn’t be too tough to remove the 47R and replace it with a 100R or a jumper…

3) Is it possible that something deeper is wrong?
For example, perhaps my jumpers aren’t so great and could be shorting?
Doesn’t seem like starting up perfectly and crapping out at a regular interval (10-15 minutes) is a short. That seems more like a power issue to me (but at this point, really, what the heck do I know?)

Has anyone else had a problem like this?
I’ve done due diligence and searched for this, and read so much about the hassle of removing the lcd, ohm’s law for calculating the resistance for different lcd’s, and what a drag it is that some creep bought up all the remaining optrex 40x2 black background displays and wants $120 for them on aliexpress… but I haven’t seen anyone bungle their Ambika quite like this.

If you were here, where would you go?

Hi. Did you use metal nuts or washers for assembling LCD to PCB. There’s a track on bottom side of the PCB that could be shorted by using metal nuts. Try to loose or remove all nuts and screws and have look.
Good luck.

Oooh! I did use metal screws and nuts on the bottom of the pcb.

I followed the instructions from tubeohm and have the lcd actually touching the pcb. The header is below. And a metal screw is going through from top to bottom, the nuts are connect below.
To be clear - there are no nuts under the actual lcd. They are below the pcb.

Although all PCB is covered by solder resist paint it’s safer to use some plastic/insulating washers under nuts and screw heads.

I’ll try this as soon as I return to my bench and post the results. Fingers and toes crossed.

Problems officially solved!

Here’s how:
I opened the case and removed the screws from the LCD - no change.
Poking about I noticed that ther were some strange behaviors in the LCD - as if it were getting worse.

I prepared to remove (and most likely destroy) LCD number two when I had a thought:
Maybe the solder didn’t make its way through the plastic holder part of the header?

I removed the plastic fitting from the header completely and soldered the opposite side as well.

Like magic - she works. She can see!
It’s wonderful.