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[xbox360hardware]

QUOTE(wilgo45 @ Jul 23 2013, 06:38 AM)

According to the diagram for Q5B1

The drain portion of the Mosfet should have 5v standby present.  The drain side is both the large tab in back and the broken leg in the middle on the front.

Double check your metering readings please
You're not reading the voltage diagram very well

With U1C1  ... both the Gate and Source legs are to Ground.  So reading from GND to GND is going to give you 0.0 ohm  - the meter is always going to find the most simple route.  Its probably not reading thru the device, but from pad site to pad site - since both are GND

You follow ?

While you are looking things over  .... Check on your 0 ohm resistors.  They appear to be marked 0000.  Or just 0.  And there appears to be 7 large ones.  Check them with continuity or resistance.  They act like fuses - for circuit protection.  If one was knocked out to save the system - then that route is still down

1. Q5B1 has no +5V checked it again

2. Which Voltage reading is incorrect ?

U1C1 only one leg is shorted to ground. which i told yesterday.

All seven 0 Ohm resistors are working

[wilgo45]

QUOTE(xbox360hardware @ Jul 23 2013, 04:52 AM)

1. Q5B1 has no +5V checked it again


U1C1 only one leg is shorted to ground. which i told yesterday.

Please don't get snippy.  I've been trying to help you.  The only one here in fact

If you have 5v standby on the board back near the power plugin - then that's good.  If the brick is producing Standby - then it can be ruled out.

The power diagram by Xperts might be when power is enabled.

As for FETs and transistors, they can't always be tested accurately while still soldered to the board.  Most reliable testing is off board.

First step might be to remove your Inductor coils.  Then test for shorts to GND between the different power rails.

But for a 360 not to power on  .... likely sources are the Power Regs, ROL board or the Cpu chip

[xbox360hardware]

QUOTE(wilgo45 @ Jul 23 2013, 08:38 PM)

Please don't get snippy.  I've been trying to help you.  The only one here in fact

If you have 5v standby on the board back near the power plugin - then that's good.  If the brick is producing Standby - then it can be ruled out.

The power diagram by Xperts might be when power is enabled.

As for FETs and transistors, they can't always be tested accurately while still soldered to the board.  Most reliable testing is off board.

First step might be to remove your Inductor coils.  Then test for shorts to GND between the different power rails.

But for a 360 not to power on  .... likely sources are the Power Regs, ROL board or the Cpu chip

 
Thanks for your help. I am just answering your questions. Which may lead to no where but any
way thanks for the response.  

First i have only +5V , according to the diagram standby is produced on the board by circuitry. That is
my understanding and from this i infer that standby is not being generated.  

I understand the confusion caused by semi-conductor devices while testing them on board. But usually
a short is quite obvious and can localized with the help of circuit diagram.

There are no shorts between the Power rails. I did check that its the first step when you have issues
of voltage not being present.

Desoldering component is risky and i have to be 100 % sure before i touch it.

Now you are saying that the CPU might cause a reset so that the +12V does not come up and bring all the circuitry up.
How do i check that ?

Second is does the CPU control Standby voltage in any way ? because i dont have standby voltage ?

According to the Xperts diagram standby should be 3.3 V

[wilgo45]

I am not saying that the Cpu is your exact problem.  Just that it can be a source of a No Power situation.  But the least likely.

Cpu does not produce standby voltage.  The brick does.  And I said nothing about reset and Cpu  - so don't know where you are getting that from

So remove the Cpu from your mind.

If you have no Standby present anywhere in the motherboard  .... then you have a bad power brick

5v is the standby.  3.3v can be found present with the 5v.  A main power reg processes the 5v standby to a 3.3   .... both will be present  .... 5v is the main

If you are finding 3.3v on your board  - then you are getting fed the 5v in a proper manner

In order to know that you have a short to GND from say 12v or 5v rails  .... is to remove the Inductor coils

Desoldering is not that risky.  Good equipment makes all the difference.  You'll want 60/40 solder and a nice gel flux.  I have removed and replaced hundreds of Mosfets.

If you have had trouble with desoldering, then your iron is too weak.  Either wrong style tip or not hot enough.  Lead free has a higher melting point.  Plus the ground plane is thick on a 360

A single plug iron won't do the job.  You'll need a Soldering station.  One with a Hot air tool makes removing multi legged transistors easy.

I'm stepping away from this topic.  Good luck

This post has been edited by wilgo45: Jul 23 2013, 09:43 PM

[xbox360hardware]

QUOTE(wilgo45 @ Jul 24 2013, 01:41 AM)

I am not saying that the Cpu is your exact problem.  Just that it can be a source of a No Power situation.  But the least likely.

Cpu does not produce standby voltage.  The brick does.  And I said nothing about reset and Cpu  - so don't know where you are getting that from

So remove the Cpu from your mind.

If you have no Standby present anywhere in the motherboard  .... then you have a bad power brick

5v is the standby.  3.3v can be found present with the 5v.  A main power reg processes the 5v standby to a 3.3   .... both will be present  .... 5v is the main

If you are finding 3.3v on your board  - then you are getting fed the 5v in a proper manner

In order to know that you have a short to GND from say 12v or 5v rails  .... is to remove the Inductor coils

Desoldering is not that risky.  Good equipment makes all the difference.  You'll want 60/40 solder and a nice gel flux.  I have removed and replaced hundreds of Mosfets.

If you have had trouble with desoldering, then your iron is too weak.  Either wrong style tip or not hot enough.  Lead free has a higher melting point.  Plus the ground plane is thick on a 360

A single plug iron won't do the job.  You'll need a Soldering station.  One with a Hot air tool makes removing multi legged transistors easy.

I'm stepping away from this topic.  Good luck

Thanks for the response. Desoldering is on expensive side when you dont know the actual problem.

As for my take on the subject is that the power brick gives a +5V to the mother board , it gives a power good
signal to the brick then it switches the +12 V , So we have +5 and + 12 V fead to the mother board.

Again there is no 3.3 v on the mother board ?

Over here the brick is giving +5 V and the mother board is not giving back a power good status. Not sure why ?

I have tried two power supplies.

So still in the unclear area where the problem is, its big mother board ?

Thanks any way

This post has been edited by xbox360hardware: Jul 23 2013, 11:06 PM