820-00923-A - How to locate a short by injecting voltage into the circuit

[imperialboard89]

Hi to everyone,

I am facing a short circuit issue on a circuit board and would like to share my situation to seek advice and suggestions from the community.

I have identified the short circuit on the PPVBAT_G3H_CHGR_REG line, and I have proceeded to isolate the circuit by removing R7060 and Q7040. Currently, I am focusing my analysis on the capacitors in the upper right part, specifically from C7050 to C7055 and from C7090 to C7099 (See here). Despite a visual inspection, I have not found any obvious physical issues under the microscope.

To proceed further, I plan to inject current into the short-circuited line. I want to clarify that I have a Thermal Camera. However, as this is my first time performing this procedure, I am uncertain about the voltage and current settings on the power supply. Considering the nominal voltage of the line is 13.1V, I am thinking of setting the voltage to that value, but before proceeding, I want to ensure the correct setup.

I appreciate any advice or information you can provide on this matter.

Thank you in advance.

P.S. I have also replaced the U7000 chip, but the short circuit persists.

 

[2informaticos]

Remove F7000 and see which side the short remains.
BTW, what is the exact value (ohm scale) of the short?

About voltage injection, read this:

HOW TO collection

I hope this "How to" collection will help our members. I will possibly modify this post in time, if updates available. Trigger SMC_ONOFF_L (PMU_ONOFF_L): It reffers to simulate power button function, when the keyboard is not connected. We need to do this when we work with the board...

boards.rossmanngroup.com

 

[imperialboard89]

I removed F7000 ad I still have short only on Capacitors, from C7090 to C7099. It means now that the short is not on PPVBAT_G3H_CHGR_REG, but it comes from PPBUS_G3H. The value on the short is 95.3 ohm. Should, at this point, try to inject voltage or is maybe better go ahead with the isolation of the short?

 

[2informaticos]

NO!
Didn't read corresponding information on that link?

Check if any big coil gives you the same reading to ground.

 

[imperialboard89]

Thanks informaticos, injecting voltage on that line like you explained on that post, I found who was the responsable of the short on PPBUS_G3H. The responsable was U8050, I replaced it and now I have not short to ground on PPBUS_G3H.

Now the voltage on PPBUS_G3H is not stuck at 13.1V how it should be, but it oscillates from 1V to 13.07V and after 1-2sec it drops to 1V again to continue this cycle indefinitely.

I found also a short on PP5V_S4, but I think is better to understand firstly why the tension on PPBUS_G3H oscillates like that. What do you think?

Edit: I found that the short was caused by U3500, I removed it and the short disappeared. Now, I go to replace all the components I had to remove and will tell you

Edit 2: Now it seems I've no short on circuit. But when I give power with usb-c and try to start the board, I get this reading (See here). It means I have 20V with oscillation from 0A to 0.2A. I noticed that the oscillation of the tension on PPBUS_G3H is still present like before and when I read 0.2A on the USB tester, the tension on PPBUS_G3H is 13.07V then when the Ampere on the USB tester drops down, the tension on PPBUS_G3H does the same. What means that?

 

[2informaticos]

"Be sure first is safe to inject voltage there; read the forum, if you are not sure!"
Seems that you didn't read full post...

How much voltage did you inject?
Your CPU may be dead now.

 

[imperialboard89]

I started gradually with voltage:

• on PPBUS_G3H I putted 10A and 1V, then I tried with 2A and 10V and found the short.
• on PP5V_S4 I putted 5V and 1A, no more than this.

I thought that is there maybe still a short somewhere, could be?

 

[2informaticos]

"10V and found the short"
I don't recommend to waste more time with this board.
It is trash now...