820-01958-A seems like CPU is bad

2informaticos

Administrator
Staff member
No need to post any picture, if you write the power rail name.
And nobody else needs to open the boardview and search for that rail.

Also try to make difference between short and (normal) low resistance to ground.
CPU core power rail has very low resistance; PPVCC_S0_CPU in this case.
Post exact reading in ohm scale.

BTW, which voltages do you get on the board?
 

Zebulon

Member
Everything on that line reads 0 resistance to ground. With the board out of the case and not plugged into anything else, the voltage is 20v and it goes from 0.07a then to zero every few seconds. the only two chips that even get warm are the T2 and U7650 and they just pulse on and off along with the amps reading.
 

Zebulon

Member
On a known working board I see the none of the same lines appear to be shorted to ground, although they do have a very low resistance to ground. How in the world would I be able to isolate if there is one bad cap on these lines or does it indicate an internal short on the CPU? None of the caps look bad. I've looked at them all many times.
 

2informaticos

Administrator
Staff member
If you get same low value as in working board, there is no short in fact.

The filter caps are more resistant than the CPU itself.
CPU is the most sensitive on that power rail; it will die before a filter cap...
 

Zebulon

Member
So I guess the CPU is dead then? The readings are not the same with a working board. On the working board the same lines all read 1 ohm and in continuity mode they will give a quick beep then stop on the multimeter, but on the broken board they go straight to zero, and a solid beep on the multimeter.
 

Zebulon

Member
Thanks, I will give that a try. I have the lab PSU. Will any of the caps on that line be fine as the injection point?
 

Zebulon

Member
After injecting 1v into that pad the PSU goes up to 0.20a. I've have looked carefully under thermal camera on both sides of the board and I don't see anything. Nothing seem even warm.
 

2informaticos

Administrator
Staff member
0.2A into pure short???
1V/0.2A=5 ohm, you've said to have 0 ohm.

Set PSU amp limit to max first; and use powerful cables.
 

Zebulon

Member
Oops! Yes, you're correct. Injecting 1v through that pad shows nothing individually getting hot, but the entire area at 10.48a and when touching the power probe it's hot at the tip with a little spark. I guess CPU is done.
 
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