820-4924 ppbus stuck at 4v

[Patricia]

Hi 2informaticos and all you other nice people

well i have a 4924 that according to the customer had some water on it ... I guess she is right but absolutely no corrosion on the board whatsoever.
It has green/orange light and the pp3v42 is actually 3.32v (bit low?) and the ppbus is 4.2v and the only thing getting a bit warm (not hot) is the cpu.
The area around U7100 looks as the rest of the board like new , unfortunately absolutely no corrosion anywhere .
The board is taking 350 mA ....
Any tips where to turn

Thank you all for any tips

 

[2informaticos]

Lot of current for a board witout PPBUS_G3H.
Bad news if CPU heats in this conditions.

Remove F7140 until you will get correct voltage at C7140.
If you still note heating CPU, it could be damaged through RTC power rail, derivated from 3V42_G3H.
U1900 heats too?
Check voltage and diode mode at its pin 1.

Also check exact resistance between pins 17/18 and 27/28 of U7100.
Post basic voltages for ISL6259; pins 1, 2, 3, 9, 12, 13, 15, 19, 20, 27.

 

[Patricia]

Thank you so much 2informaticos

Removed F7140 and i got the correct voltage on C7140 12.58V , and the cpu does not get warm anymore . The board now takes 0.073V
And YES the U1900 does get hot !!!!
Voltage on pin 1 is 0.226V and diode mode beeeeeeps

resistance 17/18 is 3.6 Ohm
resistance 27/28 is 20.9 Ohm

ISL6259 voltages
pin 1 = 3.5V
pin 2 = 17.61V
pin 3 = 0 V
pin 9 = 0.031 V
pin 12 = 3.34 V
pin 13 = 3.29 V
pin 15 = 0.046 V
pin 19 = 5.506 V
pin 20 = 5.506 V
pin 27 = 0.001 V

it seems like R7020 gets a bit warm as well on my Flir , but the precision is not the best on it (its the one attachable to the phone) so it could be something around it.

Thanks again for your answer

 

[2informaticos]

"Voltage on pin 1 is 0.226V and diode mode beeeeeeps "
What is the exact ohm value?
Remove C1910 and check again.

"pin 3 = 0 V "
Post diode mode there.
Remove C7111 and check if voltage goes up.
If yes, resolder F7140 and check diode mode on PPBUS_G3H; do NOT apply power if get strange value!
If still low, check R7110; if good, replace U7100.

 

[Patricia]

the exact value is 1.3 Ohm
removed the C1910 and the value is the same .

Pin 3 on isl in diode mode is 0.003 V
Removed C7111 and the voltage did not go up .
R7110 is 41.3 kOhm ... a bit low maybe ?
I will try to replace U7100 ......

I was completely on the wrong way .... i thought since U1900 got hot that it was the problem since with F7140 removed I got the correct value on C7140 i thought U7100 was ok .
Thanks

small update , replaced the U7100 and the values are back to as before ppbus 4.03V and the board still takes 0.354 A... the only difference is that L7130 gets hot now

 

[2informaticos]

"resolder F7140 and check diode mode on PPBUS_G3H; do NOT apply power if get strange value! "
???

Do you get correct CHGR_ACIN after changing U7100?

 

[Patricia]

CHGR_ACIN is now 4.48 V after changing the U7100 so at least that is now ok
Diode mode on ppbus is 0.176 V

removed U1900 and measured all the pins and found short on the following pins: 1 , 2 , 5

 

[2informaticos]

What is the exact ohm value to ground at pin 1?
Remove C1910 and test again.
If still low, there are 3 caps more, C8090-92.
If none bad, then dead CPU...

 

[Patricia]

The exact ohm value is 1.4 Ohm to ground on pin 1 . Even with the C1910 removed it is shorted ... does that mean that the short is in the board , since the U1900 is removed as well ? It seems that I will have to give up on this one . The C8090-92 are ok (unfortunately) .
Thank you 2 informaticos for all your help .
Are you the only moderator left on the forum ? All the latest posts i notice that you take , it must be a lot of pressure only on you , not fair .
Have a nice day and all the best to you

 

[2informaticos]

Dukefawks still helps here, when dificil case.
Nobody has more experience than him...

 

[Patricia]

hehehehe that may be true , but mostly we get "crap under the smc" or dead cpu from him you really make an effort to help and you dont tell us how stupid we are for not knowing how to repair the board , if we knew we wouldnt be here
Anyway thanks a lot