A customer brought this set in a few days ago, she had taken it to a prev ious shop where they replaced the power supply and mainboard, but failed to fix the problem (yet they still charged her $250). She brought the two old boards, and the supposedly-new ones were still installed. Initially, the relay would click and the power light would turn green, bu t nothing else would happen. I was able to get the backlight to power by tr icking it (3.3V to backlight_on) but nothing else happened. I noticed that once I returned the backlight circuit to normal, the backlight would now po wer by itself. Both power supplies produce the same symptom, and at this point I can rul e them out as they appear to be functioning correctly. But there is a diffe rence with the mainboards. With the original board installed, the power lig ht and backlight come on and stay on, but nothing else happens - no click f rom the speakers etc). With the "new" mainboard, the same happens but the s et powers off after about 10 seconds, with no error blinks. I tried to find some evidence of output to the T-con board using a scope, but there appears to be nothing at all - no discernible blips etc when var ious functions are pressed. I have used this method in the past to successfully diagnose plasma sets, so at this point I'm inclined to suspect a bad mainboard. I also would hav e to conclude that the previous shop either received a bad board (which the y should have returned under warranty) or installed a known bad board and c harged the customer for a new one (in which case they shouldn't even be in business). Is there anything else I should check before ordering another mainboard? The customer doesn't want to gamble much more money on this set nor do I wa nt to gamble much time on it. Thanks for any advice.
- posted
9 years ago