PSP Repair skills

Hi i have a little problem with my psp.
the bussystem hang up after about 10-20 minutes of gaming . So it won't be able to open the memorystick, settings (all menue points) but i can switch the menupoints and it wont to save a game. this is very bad, when you play mercury and finished after a couple of time to try finishing the level. A firmware update helps nothing. i had 2.0 with the problem and now 1.5 with the problem. the problem is: i cannot send my unit back to sony cause its a jap version. :( So i think with the replacement of the right chip its possible to fix the problem. :D Oh don't worry i'm an electronics engineer. :) first i've thinked there is a slack joint on a flat cable. i've opened not at all, i've opened only to the mainboard. and found nothing to there. i Know the cable to the memorystick pcb is under the main pcb. Can anybody help me? is there problably a psp repair men? :D Is there a PSP hardware test in the firmware, by pressing a lot of combinations of buttons?
Please write any ideas you have...

Thanks