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

imperialboard89

New member
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

Administrator
Staff member
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:
 

imperialboard89

New member
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

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

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

imperialboard89

New member
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?
 
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2informaticos

Administrator
Staff member
"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

New member
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?
 
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