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820-3115 with blown hole on u9410

gadgetfix

gadgetfix

New member
hey there,

this board had a bit of corrosion after some cleanup was running fine. about a month later it unfortunately died, opened to inspect a hole in u9410. Now pp15v_t29 is completely short to ground, i have removed almost every component but short is still there?

would it be safe to inject voltage into that line to see what gets hot?

thanks
 
J

JohnB8812

New member
Sounds like it is shorted possibly in layers of the board. You can inject voltage and see if you can find it. When you find it, TBT is not going to be useable ever again FYI.
 
Alan.L

Alan.L

Member
i would remove Q3880, U3890 and R0960 be done with it. i think that should disable the pp15v_t29 line

if you want to find the short then just start with from small until all the way up. no more than 15v obvious. I find pouring some alcohol will help, you still start to see smoke then poke it with a tweezer while wearing glove.
 
Last edited:
gadgetfix

gadgetfix

New member
Alan.L said:
i would remove Q3880, U3890 and R0960 be done with it. i think that should disable the pp15v_t29 line

if you want to find the short then just start with from small until all the way up. no more than 15v obvious. I find pouring some alcohol will help, you still start to see smoke then poke it with a tweezer while wearing glove.
Click to expand...

thanks but after testing everything i found short where it blew. so its in the pcb layers, I scratched it back uv cured and short is gone. in this case is it best to still remove the parts you have mentioned? and im assuming u9410 will need to be replaced on the board too?
 
2informaticos

2informaticos

Administrator
Staff member
You don't need U9410 if thunderbolt area is damaged.
Also you can remove other chips form that area; can be reused in other repairs...
 
gadgetfix

gadgetfix

New member
Hey there, i removed Q3880 and U3890 however i got nothing on R0960
I now dont have green light. ppbus is present as well as pp3v42

i will test other voltages and report back.

thanks for your help.
 
gadgetfix

gadgetfix

New member
SMC_adapter_L 3.44v
pm_batlow_L 0v
pm_rsmrst_L 0v

u6900
p1: 3.49v
p4: 3.49v
p5: 3.49v

u6901
p1: 3.33v
p2: 3.33v
p4: 3.49v
p5: 3.48v
 
2informaticos

2informaticos

Administrator
Staff member
"pm_batlow_L 0v"
PCH will not start power on sequence this way.
Are you using original 60W charger?
Try 85W charger too.
Also see if starts in SMC bypass mode.
 
2informaticos

2informaticos

Administrator
Staff member
"all good - nothing low"
I told you to check continuity on that line, not resistance to ground.
Do you get 3.3V at central pin?
 
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