Xbox v1.4 no power, good PSU, good CPU caps

[SoftMachine]

I have a v1.4 that doesn't seem to be getting power at all, zero response from power/eject so I've tried a bunch of stuff:

- Replaced 3x 3300uF 6.3V, 3x 1500uF 6.3V, and 2x 3300uF 10V caps, all the big ones

- Checked continuity on those 4 lines that usually get rotted, 3 were good, rebuilt 1 and confirmed continuity with the top of the board

- Reflowed the 20 pin ATX header

- Tested with 2 known good PSUs

- Tested with 2 known good front panel PCBs

I haven't seen this behavior (or lack of) before and had it not be bad caps, but if there's something to be tried short of an entire recap, I'm unaware of what that would be. Anyone have any ideas?

[SoftMachine]

https://imgbox.com/dAD6ygvA
https://imgbox.com/pG2sQnQk

Edited April 22, 2023 by SoftMachine

[bolofski]

I would probably do the full trace rot repair first just to make sure the lines are good, especially if you say there was a problem with one of them

[KaosEngineer]

Make sure that the power supply is providing the standby voltage level (3.3Vdc in the STB column below) to the motherboard.  Without it, the System Management Controller (PIC processor) cannot turn on the remaining voltage/power rails of the PSU.

[SoftMachine]

3 hours ago, KaosEngineer said:

Make sure that the power supply is providing the standby voltage level (3.3Vdc in the STB column below) to the motherboard.  Without it, the System Management Controller (PIC processor) cannot turn on the remaining power rails of the PSU.

 

Thank you, the PIC is getting 3.3V STB on pin 20 (VDD) http://ww1.microchip.com/downloads/en/DeviceDoc/30605D.pdf

Would you suggest maybe replacing the PIC with one from a donor board?

 

Edit: well I tried jumping power on to ground on the back of the board, then tried replacing the PIC, nothing happening

Edited April 22, 2023 by SoftMachine

[KaosEngineer]

1 hour ago, SoftMachine said:

Thank you, the PIC is getting 3.3V STB on pin 20 (VDD) http://ww1.microchip.com/downloads/en/DeviceDoc/30605D.pdf

Would you suggest maybe replacing the PIC with one from a donor board?

 

Edit: well I tried jumping power on to ground on the back of the board, then tried replacing the PIC, nothing happening

There are other things to check before swapping the PIC processor.

First, make sure that the power button signal is reaching the PIC processor.  While pressing and releasing the power button, measure the voltage level on pin #18.  It should change state (voltage level). When depressed, you should read 0Vdc and when released 3.3Vdc.

Next, the output from the PIC processor, PowON - pin #16, should change state.  0Vdc = power off, 3.3Vdc = power on.

 

[KaosEngineer]

From the tiny bit of information I've found on the Xbox PSUs, they have overvoltage and overcurrent protection.  There may be a problem with the output voltage levels detected by the PSU when turned on and it almost instantly shuts off or a short may cause the attached circuitry to draw too much current which will also shut off the power supply.

Since the Xbox's PSU is a switching power supply, you should not try to power it on without a load present/connected.

Some switching power supplies will not function properly without at least 1/2 of their load being pulled by the connected circuitry.  For the Xbox, this means the motherboard, DVD drive, and hard drive.  I don't know the exact minimum power draw the Xbox's PSU requires to operate.

 

First, disconnect the power cable from the hard drive then try powering on the console.  Does it power on?

Next, disconnect the power / control cable from the DVD drive.  Does it power on?

Next, disconnect the IDE cable from the motherboard.  Does it power on?

 

[Onufree]

Similar problem - after changing 3x 3300uF 6.3V console turns on for 1 second (without any diods and lights). Any troubles with power supply or caps?

Before I changed caps console doesn't run at all.