SparkFun Forums 

Where electronics enthusiasts find answers.

General project discussion / help
Did you make a robotic coffee pot which implements HTCPCP and decafs unauthorized users? Show it off here!
By TMJJ
#199058
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.
Image
Image
Image

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
By paulvha
#199064
your images did not make it (use full editor and preview to include). All I can think of is the power supply. An LCD can take easily 2A and maybe there is to much resistance due to smaller print tracks. Maybe check the 5V and 3v3.
By TMJJ
#199070
Hmm, I can't edit my previous post. So I will add the images here.
So I attached the files. I can see them in preview. I hope you to ;)
You do not have the required permissions to view the files attached to this post.
long long title how many chars? lets see 123 ok more? yes 60

We have created lots of YouTube videos just so you can achieve [...]

Another post test yes yes yes or no, maybe ni? :-/

The best flat phpBB theme around. Period. Fine craftmanship and [...]

Do you need a super MOD? Well here it is. chew on this

All you need is right here. Content tag, SEO, listing, Pizza and spaghetti [...]

Lasagna on me this time ok? I got plenty of cash

this should be fantastic. but what about links,images, bbcodes etc etc? [...]