Hi. I got broken Xbox 1.5 Mobo. It hasn't any visual damaged points. On original BIOS it turns on, but no video/audio. When i plugged an Aladdin XT+ chip, console is fragging (3x restarts). I made connections from LPC to GND and 3.3V.

no vid or audio but no frag..
thats a new one for me lol. only time ive ever had that is when installing extra ram and i was testing for frag's between adding 1 chip and the next. so unless it has extra ram which would probably be a good place to start your examination.
i would start by looking at the scaler chip "focus" or whatver it is.

also the 1.5 boards have a diferent lpc to a 1.2-1.4 i assume you know this because to my knowlage thats the only way to tell if you have a 1.5 vs a 1.4
so your going to need a multi meeter if you havent tested already.

I made connections from LPC to 3,3V and GND. Any other ideas? I will try another modchip for few days.