820-3115 PP3V42_G3H short (another one)

[djdblaster]

Hi,

no history on this one. No water damage as far as I can see. PP3V42_G3H measures 0.007V in diode mode or 18 Ohms.

I've removed L6995 to see which side is shorted - system side it is.

I've injected 1V into the PP3V42_G3H and the current draw was around 600mA, pointing at U7000, which was removed after.

Now with 1V injected the current draw is around 65mA and SMC gets barely warm. I don't see anything else on camera.

What should be my next step?

 

[JohnB8812]

Inject 3.4 volts and see what gets hot.

 

[djdblaster]

Can I damage SMC like that? Cause on one other board, I injected 3V and SMC could be bad right now...

 

[JohnB8812]

If the SMC is dead, it doesn't matter if you inject .5 volts or 3.4 volts, it will be dead. PP3v42 is not really rail to worry on voltage as long as you don't go above 3.42. PPBUS is the rail you have to be careful of because of the CPU and its high side fets.

 

[2informaticos]

Nor even 4V on 3V42 rail will damage anything.
As general rule, do not exceed 120% of the nominal voltage.
Always start injecting with low voltage and go up slowly...

 

[djdblaster]

I've injected 3.4V, nothing heats up except SMC, barely, 32C.

 

[JohnB8812]

If the SMC is heating, remove it and see if the short goes away. Sounds like a shorted SMC

 

[djdblaster]

SMC is removed, there is no short on PP3V42_G3H.

I need to get another SMC, right?

 

[2informaticos]

From donor board, same model...

 

[djdblaster]

They're are very hard to get. I was expecting this answer, but a tiny part of me was hoping for: Try reballing first.

 

[2informaticos]

You can locate corresponding pins of the SMC for 3V42, as ground pins too.
Then check between these chip pads (out of board).
If you still get low value, forget about reballing...

 

[JohnB8812]

Best to get a donor I usually order 2-3 to make sure I get one with a decent SMC

 

[djdblaster]

JohnB8812 Where do you get them? eBay?
2informaticos Just checked, it's still shorted. Around 80 Ohms. Oh well...

 

[2informaticos]

I've got "good" scrap boards on eBay from galaxyelectronics2015 seller.
You can get better quote closing deal outside eBay.
Contact seller directly with PM, or through Skype ID, Paul Lee...

 

[djdblaster]

Thanks!
How about used SMC's from Aliexpress?

 

[2informaticos]

Only from donor boards.
I never ordered SMC from Aliexpress.
But actualy I prefer to buy chips from Aliexpress instead of eBay.
They send all with tracking number and have good buyer protection now.
However, never buy new SMC chips.

 

[djdblaster]

Agreed.
I'll try my luck with Aliexpress then if they reply that chips were good pulled.