Dear all,
I’m writing here my first post because I have some really strange thing happening. I hope to find a experience pcb designer who can point me in the correct direction,
First a short intro of my project:
I’m building an embedded system with a TI AM335x system on module(SoM). For this SoM I builded a carrierboard. The embedded system will be used in my tractor. Here I want to read can data from the bus into the system.
My first prototype was a 4 layer pcb. Here I had no problems with the LCD (LVDS 1024x600). Now due to other imperfections I made changes to my pcb.
Also due to costs I reduced the amount of PCB layer to 2. Which I think should not be a problem.
Now Last week I was testing everything. The canbus works, the outputs work… The I found out that my LCD screen doesn’t work correctly. The colors are incorrect. When I push my 50 pin connector it gets better. So I thought that it was probably the connector which wasn’t soldered very well. So I desoldered the connector, cleaned the pcb and resoldered a new conenctor. After I inspected the connector under a microscope and everything looks very nice!
So I tested the LCD again. I still have the same problem. When I push the ribbon cable between the LCD and connector, the colors changes. At this point I started to stress!
After I contacted the vendor and asked him if he has an idea of whats going wrong. He told me that it was probably that my transmission line impedance isn’t 50 ohm (Which he never told me it should be!) and that I need to refabricate my pcb and ask to match my LCD data lines to 50 ohm.
Now I’m looking for somebody who could tell me this is possible and give me some support on how to test this.
I’m very sure that the problem is within my pcb and that it is not software related. On the previous board there where no issues with the screen.
The following images are the schematics of the screen and a printscreen of the pcb.
So, can somebody confirm what the vendor says?
Is it possible to test this changes? Or should I try other things?
Maybe changing the 33ohm resistors on the pcb to an other value?
Hopefully somebody can give me some hope.
Kind regards,
TMJJ
