820-3115 - Brain dead.

[gcain]

Customer said it was showing colours on the display from time to time then just went dead.

USB mouse doesn't light up, never chimes, PRM Reset does nothing and fan spins high.

CPUVCore @ C1655 is 0.678v and Diode to ground is 0.001v

 

[gcain]

So I noticed the TP for CPUIMVP_ISUM was corroded and broken. I ran a jumper from R7407 -> R7406 and to R7410.

Now, with no ram I get a ram beep. If I insert ram the fan spins for a few seconds, then stops and spins for a few seconds again, then stops etc....

 

[gcain]

It's like it's trying to pass POST but something is browning out and stopping the process.

 

[gcain]

PGoods are unstable.

CPUIMVP_PGOOD sits at 3.3v, then bottoms out to 0v, back up again.
CPUIMVP_AXG_PGOOD floats around 200mV.

 

[dukefawks]

Ugh, this can be so many things There must be more corrosion somewhere else, inspect carefully.

 

[gcain]

Ugh, this can be so many things There must be more corrosion somewhere else, inspect carefully.

The board is in oddly good condition aside from that single test point. I have gone over it closely and not found anything.

Could that test point link to or something else?

 

[gcain]

Actually, a test point near C7524 is a little corroded too.

 

[dukefawks]

It could be anything, there is no way to diagnose this with measuring things. Inspect everything, maybe give the SMC some flux and heat.

 

[gcain]

I ran some flux around the SMC, but no change.

Have noticed that CPUIMVP_TONA & B drop down to 0.6v when the fan spins, then pop up to 12.58 when it stops @ R7402::1 & R7403::1 but the voltage on ::2 stays at 12.58v. Could this be a faulty U7400 pulling it down?


After this I'm out of ideas as the board looks spotless.

 

[gcain]

Actually a working board is the same.

Out of ideas. :/

 

[dukefawks]

Have noticed that CPUIMVP_TONA & B drop down to 0.6v when the fan spins, then pop up to 12.58 when it stops @ R7402::1 & R7403::1 but the voltage on ::2 stays at 12.58v. Could this be a faulty U7400 pulling it down?

That is totally normal.

This board is not going to happen, sorry.