Power botton stay red
If the PSU is confirmed working, it is either something wrong with the microcontroller in the southbridge that controls the power on sequence, the linear regulator that powers it and/or the ROL board, or a short in the 5V standby (blown capacitor, transistor, etc).
The easy way to determine which one of these is the problem is to look at the light on the PSU, if when you plug it into the 360 it turns red briefly (or stays red), there is a short on the standby power (If the short was on the switched supply, the 360 would power up then flash 3 red lights with error 0001 or 0002, or power up for a split second then shut itself off). Also measuring the resistance from 5VSB to ground is a pretty sure fire way to tell
If the 5V standby power is NOT shorted, then the issue is either in the power button on the RF board (easily tested by powering up the box via another method), the southbridge, the the voltage regulator supplying it.
The two regualtors are U5B1 (3.3V) and U5B2 (1.8V). They are located on the top of the motherboard near the back, jsut to the left of the large screw hole in the center of the motherboard (near the fans). The large tab opposite the 2 smaller pins is the output of each regulator, so they should measure 3.3v and 1.8v respectively when the 360 is in standby (off but plugged in).
If those measure ok, then I'd say the southbridge is dead (that motherboard is nothing but a nice paperweight)
Dec 07, 2009 |
Microsoft Xbox 360 Console