XBOX 360 Jasper

[Wigs]

Hi,
I trained many years ago as an electronic engineer, in the 80's, but never really went into the field. Things are a lot different these days, components the size of specks of dust instead of family cars etc. Anyway, I have a strange problem with my xbox 360, I noticed one day that it would switch itself on and the disc tray would repeatedly open and close. I searched the internet for information, to no avail. I did find some circuit diagrams, it appears as though the machine thinks the ODD button is being continually pressed. I found the section where the eject button is and figured there should be a constant 3.3v to the southbridge when in standby and when the ODD button is pressed this is shunted to ground sending a low signal to the southbridge telling the machine to switch on, if it's off, and open the DVD tray, then each successive press would open or close the tray. These are the exact symptoms. I figured there was most likely a short somewhere on the 3.3v standby rail. Apart from this, the machine works perfectly, in that, you can browse the dashboard and start a game. Of course, you can't turn the machine off as it will just restart itself. If anyone has any idea or advice it would be greatly appreciated. I've checked the that the button is not faulty and the resistors that control the signal and they're fine. The only other thing I think it could be is the standby voltage that supplies the resistors. It may be a common problem but I couldn't find any useful information about it. Thanks.

[stj]

test the drive by powering it without the sata cable.
make sure it's not the drive having tray position problems.

[Wigs]

Hi,
Thanks, I know it's not the drive. I'm now wondering if maybe the 3.3v regulator may have blown. I'll check it today if I get around to taking the thing apart again.

[stj]

it's very strange,

[Wigs]

I'm absolutely confident it's a failure of the 3.3v standby rail. But where?, is the question. I'll take some voltage readings and test for shorts in the rail. I bought a Series X just so I could continue to play my 360 games. But, I'd rather have the 360. I was just about to RGH it, too.

[stj]

did you look at the schematics?

[Wigs]

I did look at the schematics, that's how I know the DVD button and the 3.3v stdby are linked and a missing 3,3v would cause the exact symptoms.

[stj]

well if it's missing maybe there is a short on the rail.
ceramic cap possibly.

[Wigs]

No, I checked the voltages that should be present on the regulators from a diagram and they are all right, only, my board revision doesn't have the 2 standby regulators for 3.3v and 1.8v so I don't know where the standby voltages are generated. I believe it's a Tonasket board. I'm beginning to lose faith now. I just checked and there doesn't appear to be a short between the regulators and ground.

[momaka]

It very likely won't be a missing/shorted voltage rail. Like a computer / PC motherboard, the Xbox 360 motherboard checks if all of the DC voltage rails are present and correct at boot time. So if any rail is not there, the board won't boot.

Try stj's suggestion of removing the SATA cable from the ODD and see if the issue disappears. If it does, then the issues is with the optical drive somewhere.
My guess would be the eject button on the optical drive is marginal and making partial contact from random room vibrations. You won't be able to see this with a regular multimeter, but could measure it with an oscilloscope if you're willing to stare at it for a while till it happens. I had an LCD monitor with this issue where the OSD menu would randomly pop-up. I couldn't open the button to clean it (it's one of those buttons that's not exactly easy to close after opening.) So I just disconnected the power button and that fixed my issue. So I suggest trying the same thing if you find your Xbox 360 is fine with the test where the SATA cable is removed from the optical drive.

[Wigs]

Thanks, you're right about the standby voltage, but there's a resistor fed directly from the 3.3v standby, the other end connected to the switch which is then grounded when pushed, I was thinking maybe a trace from the standby rail had corroded so there was no standby voltage to the resistor acting as a constant short at the switch, I've checked, I think, and this isn't the case. I did remove the drive and shorted the tray closed pins and the same problem persists. I did suspect the switch,but tested it and it seemed fine, you're right about the possibility of it being a hard to detect defect though, so I may remove the switch, which would result in a constant open circuit and if the switch was the problem the issue would go away. I'm not hopeful though. It seemed like it was going to be such a simple problem to resolve, I mean, there's only a switch and two resistors controlling the signal to the southbridge, that I can see would cause these symptoms. I've replaced the RF board but this had no effect. As I say, the symptoms are exactly what you would expect from constantly pressing the eject button. The only other thing I can think of, is, maybe, a bad connection at the southbridge or a dodgy southbridge. From your other posts I can see you know a lot about how the 360 operates, so I really appreciate your input.

[Snapman]

https://xbox360hub.com/wp-content/up..._Schematic.pdf
https://xbox360hub.com/wp-content/up..._Schematic.pdf