xbox 360 blowing mosfet

[waldoalvarez00]

Hi Folks:

I have an xbox 360 that had a shorted USB pin. After unbending it and turning it on it came without video and red ring. I tried the towel trick and it came up with video. Then the power source led turned red and I heard a mosfet failing. I tested the mosfets and found the two 5v mosfets were shorted (they showed as two resistances on the tester). I replaced them but now the one closer to the CPU is shorting everytime I power it on. If I remove it it starts with red ring.

Any ideas of what could be failing? Maybe a shorted capacitor? What tests should I do?

Regards

[ReeceyBurger123]

What else have you checked for S/C in that area ?

[momaka]

Post a picture of your board and tell us exactly what parts you think failed (i.e. Qxx, Cxx, etc.) and what you replaced them with.

Also, the towel "trick" is simply that - it is a crappy temporary repair at best, and usually does more damage than good. If you got an RROD with a secondary code typical of GPU failure, then do a reflow on the GPU. Here is a rather crude but fairly easy method:
http://www.badcaps.net/forum/showpos...3&postcount=15

Again, do NOT use oven or towel "tricks" - they are always done by people who don't know what they are doing. Spending a little bit of money to get decent tools (a heatgun and temperature probe) is a must if you want to do it properly, and especially if you intend to keep your 360 console working for as long as possible or fixing other 360 consoles.

[waldoalvarez00]

Ok I replaced those two with ones from another console, it got fairchild ones (both were damaged) so I putted two On semiconductor new ones (tested as good on the transistor tester) http://www.onsemi.com/PowerSolutions...o?id=NTD60N02R



You see the one closer to the CPU next to the small black capacitor blew two times. No smoke no holes no nothing. The fan tries to start for a second then it stops entirely. It gets damaged and shows as to resistors on the tester. Maybe the controller chip? Just wondering. I don't have oscilloscope to test.

Are you sure this gotta do with GPU reflow thing? That part of the circuit I think feeds USB and drives with 5V. Testpoints on all other parts give me 0v readings for RAM, CPU VRM and GPU VRM. Standby testpoints are the only ones good, 3.3v and 1.8v on the upper side of the board. No more voltage readings anywhere else.

I know it gets +12 v on the upper Mosfet base for a short while if I remove it and start the console. Then goes back to zero and give the three rings.

Yes I know towel trick is bad stuff. I just tried it to test it. I had no solder station then. Strange thing is it started for sure and I got video. Then it lost video but was still making sound (so yes maybe GPU reflow as you say is needed). After that trying to start it again it gave me sound, the Mosfet failed and the power brick turned the led red.

I think there are two things here. GPU problem and something else. I am looking to find that other problem and then jump into GPU reflow.

[waldoalvarez00]

Originally Posted by ReeceyBurger123

What else have you checked for S/C in that area ?

I don't see short circuits in that area. I put the Meter in diode mode to test continuity and there are none with ground.

[stj]

when it shorted, did all 3 pins short together?
if yes, then whatever is driving the gate pin may be damaged.

[waldoalvarez00]

Originally Posted by stj

when it shorted, did all 3 pins short together?
if yes, then whatever is driving the gate pin may be damaged.

Not really sure. They show resistances in all the damaged Mosfets so yes could be the case. So what is driving the gate should be connected to a resistance. I have a 360 schematic, I attached it. I think is PAGE_TITLE=VREGS, V1P8 AND V5P0. So seems to me that part of the circuit is driven by the NCP5425 (http://www.onsemi.com/PowerSolutions....do?id=NCP5425) through those resistances R5F5 and R5F6.

[waldoalvarez00]

Sometimes in SMPW I get the Mosfets blown when the feedback is damaged as they run on superhigh duty cycle. Also with shorts somewhere else as the tension output is so low the duty cycle is way too high for the Mosfet.

[waldoalvarez00]

I noticed this model is not the same exactly as the one in the schematic (Xenon), it is a Falcon board. It has no SMD resistors coming from the controller to the gates and has this controller http://www.analog.com/en/products/po...s/adp1823.html

I tried another thing. I removed the USB ports since they were bent anyways and just in case they had some shorts. I have a Xenon board bent and broken picked from the garbage, with some stuff missing but the USB ports and many things are ok.

So putted another mosfet and took the risk to power it on. Well this time it holded and didn't got damaged but the power brick is sensing something as the console spins the fans for a second and then the power brick turns the led red activating sort of an overcurrent protection mechanism.

[stj]

Originally Posted by waldoalvarez00

Not really sure. They show resistances in all the damaged Mosfets so yes could be the case. So what is driving the gate should be connected to a resistance. I have a 360 schematic, I attached it. I think is PAGE_TITLE=VREGS, V1P8 AND V5P0. So seems to me that part of the circuit is driven by the NCP5425 (http://www.onsemi.com/PowerSolutions....do?id=NCP5425) through those resistances R5F5 and R5F6.

do you have schem's for other xbox boards?

[waldoalvarez00]

Originally Posted by stj

do you have schem's for other xbox boards?

I didn't but found them here is for Falcon. Enjoy

[keeney123]

So they have a phase Lock loop on the power supply. They must have a problem with the frequency of the power supply drifting?

[stj]

Originally Posted by waldoalvarez00

I didn't but found them here is for Falcon. Enjoy

nice

[waldoalvarez00]

Originally Posted by keeney123

So they have a phase Lock loop on the power supply. They must have a problem with the frequency of the power supply drifting?

Sorry don't understand this. Where they have a phase lock loop and how it could be related? PLL are used for clocking right? How it is related? The chip seems to have some internal clock with external possibility not used in the design and osc frequeancy selectable through a pin.

[keeney123]

PLL was use for FM radios so that when the frequency carrier started to drift a feedback circuit would correct it on the input oscillator. I am assuming that with the a power supply that is frequency modulated the modulator has a tendency to drift so they are using the PLL to correct this error.

[diif]

Here's the Xenon stj

[stj]

Originally Posted by diif

Here's the Xenon stj

that was posted earlier in the thread.

[keeney123]

It would appear that the Phase Lock loop control is on page 50 at this IU7U1

[waldoalvarez00]

Originally Posted by keeney123

It would appear that the Phase Lock loop control is on page 50 at this IU7U1

Just a buck converter for the CPU. It just lowers the 12v from input to the VID specified by the CPU.

[keeney123]

So why is is listed as phase 1, phase 2, phase 3? You will also notice the output looks back to the input through the V_CPUCORE as a reference. I have not look up the IC, but it would seem to me that the different phases are being sent up by what is being feed back form the V_CPUCORE and this is what is causing when the phases are sinking.