Following a series of unfortunate events I’ve managed to uncover the reason and the solution to the issues of this topic title.
Ive got an MD SPS1 MK1 a while back, and decided to upgrade it to a B/W screen. Ive done the job myself and I wasnt prepared to handle the solder stuck in the vias. Long story short, managed to fit the screen but some of the traces got damaged so if the screen was in a particular position, the MD started up fine, when i applied small amount of pressure on it, the exact same weird characters and failed boot attempts occurred that was mentioned in many posts here.
Weirdly, every single time this issue occurred and I was able to get the MD into self test, the test always came back 100% functional, none of the dsps or ram was damaged. This got me thinking.
I was trying to put layers of rubber between the screen and the top cover to achieve the optimal pressure to keep the device functional, during this, Ive managed to achieve all of the errors other users faced (black screen no logo no boot,white screen no logo no boot,clean logo bot no boot,clean logo no boot that shortly starts to display weird characters,weird characters only etc… )
After a long time of happily running my butchered MD at “just the right pressure on the cover plate/display to operate” , yesterday it gave in suddenly, without touching it, it just restarted suddenly and no boot, flashing logo.
I got fed up and serious, precisely removed all the pins and soldered a 20 way ribbon cable between the display and the main board. I ve also connected the broken traces by wires.
The operation ended just as I expected,the MD booting immediately, and functions without any issue.
My conclusion is this:
The weird characters,stuck in boot loop etc… issues are a result of a connection fault between the double sided pcb and the pins that hold the screen in place. I found that this pcb/via/pin/screen structure is very rigid, and through many heat cycles, one point of contact out of the 4 layer x 20 fails, causing these issues.
It came to me as a revelation yesterday, after a LOT of suffering, I hope that this may save other users plenty of time and headaches.