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820-00165 PPBUS_G3H shorted to ground

B

BCN_Techs

Member
Hi Guys,

Have a 820-00165 board. F7140 was blown so changed it. Getting 8,6V on pin 1 but pin 2 is shorted to ground. I have removed F7140 and injected voltage on pin 2. Nothing is warming. Absolutly nothing.

Checked R5450 and seems that PPBUS is shorted to ground through PPBUS_S5_HS. Removing R5450 short on PPBUS-G3H desappear.


Any advice? Inject voltage on PPBUS_S5_HS_Computing_ISNS and check what is getting warm again?


P.S. Also checked meanwhile Q7310/20 and Q7430/630 not seems to be the reason of the short
 
Last edited:
2informaticos

2informaticos

Administrator
Staff member
I really don't know how many times need to repeat how, where and when inject voltage.

At least you located the short on PPBUS_S5_HS_Computing_ISNS.
Unfortunatelly already injected voltage on PPBUS_G3H; hope started with not too much!!!
Compare that short (only you know exact value), with ohm value to ground at L7310/20, L7430 and L7630.

"Also checked meanwhile Q7310/20 and Q7430/630 not seems to be the reason of the short"
Without exact values, we cannot confirm anything.
If you are sure about these, then should be just a cap on PPBUS_S5_HS_Computing_ISNS power rail.
This is also a common fail; usually one of 62uF/11V near CPU.
 
B

BCN_Techs

Member
2informaticos. Thank you again. It was C7373. VIsually it is perfect. Had to remove all caps and return them one by one.

About injecting. I did it because many people on this forum after facing PPBUS shorted recomend that (Like Duke). Sure i started injecting in 1V and max was 2V.
 
2informaticos

2informaticos

Administrator
Staff member
I'm sure dukefawks never recommended inject voltage before checking high-side MOSFETs.
I learned that from him!!!

If you know all high-side MOSFETs are OK, then is safe to inject even 9V there.
However, ALWAYS start with lower voltage; this way avoid bench power supply to get blocked.
 
B

BCN_Techs

Member
2informaticos what is the way to check that high side mosfets are ok? U mean Q7311/10/21/20 and Q7630/430 right?
 
2informaticos

2informaticos

Administrator
Staff member
Drain - Source...
The one with closer ohm value to 000 is shorted.
If none, then you are safe to inject voltage; until 120% of PPBUS_G3H.
Don't forget to check all secondary suplies, not only CPU one.
 
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