very tricky display problem (I think?)

[John E. Finster]

Hi, I´m in desperate need of assistance.

 

I´m building a Midibox_NG with 18 ssd1306 displays and I´m in the final stages. I already assembled the frontpanel and put it in a case. At first everything was fine, but then I caused a small short between the Vss-line and SDA-line for the displays (not 100% sure about the shorted lines though). The displays began to flicker, when I used some button or encoder. I thought this had to be a ground-related problem and after a long night of searching I found the short and fixed it. So far so good.

 

But now the displays malfunction again, but in a different manner:

After I power up the box, everything is fine. I inserted a syntax that puts a small "ready" message on every display and that works. After a short while (~1 minute or so) and after I´m loading the ngc file I´m working on I notice a similar fault like the one above:

First, the 9th display doesn´t seem to work anymore, same for the 16th. The other displays work at first, but after a minute, little by little, they begin to flicker and the characters shift positions on screen, when I press a button.

 

After another night of searching I´m pretty sure, there isn´t another short an the board, but there are hundreds of soldering points and I don´t even know where to start.

 

I also noticed that the ampere of the psu is fluctuating between 0.4 and 0.7 ampere a minute after I power up the box. That didn´t happen before I caused the initial short and everything was fine.

 

Please, I really could need some help on this. At least some kind of plan, how I could narrow down the fault.

 

Thanks

 

my regards

[John E. Finster]

Hi, I´ve just solved the problem and I´m amazed about my own stupidity. I built a small pcb extension for a 3rd and 4th midi in/out into my box, which didn´t work. I can not tell yet, why it didn´t work, but for the moment I let it go because this was not a priority for me.

 

But I didn´t disconnect the defective pcb from the core.....

 

That caused all the problems I had the last 3 days, the malfunctioned displays, ampere fluctuations, voltage spikes on the core, the broken sd card,...

 

Anyway, thanks for reading this testimony of my own asininity...

 

my regard