[SOLVED]820-3332 dead no light on charger

[shlom]

hello


working on a 820-3332-a logic board

looks very clean, no liquid damage, under the microscope couldn’t find anything that looks bad…

the board is dead, no light on the charger..


on F6905 i get around 16.73v on each side

ppbus_g3h is 3.295v

PP3V42_G3H is 3.393v


resistance to ground on ppbus_g3h showing 6.8 m ohms and dropping, on diode mode showing 0.422 v



on PP3V42_G3H showing 2.929 k ohms

seems to be ok, also the voltage on pp3v42_g3h but still no green or orange light on charger… (maybe bad dc in board? will try to get another one tomorrow to test with..)




i checked the one wire circuit

on u6900

pin 5 = 0.728v

pin 4 = 0.780v

pin 1 = 3.378v




a note :
u8900 seems like been worked on with remaining of flux, but i doubt it has anything to do with the issue of no power…



any advice on what to check next?


thanks…

 

[2informaticos]

Check voltages at pins 5 & 8 of U5110.
Post some voltages at U7000, pins 1, 2, 3, 19, 20, 9, 15, 27, 28.
Alsos check for short/low value at secondary supplies (big coils).

 

[JohnB8812]

Check resistance between pins 17/18 and 27/28 of the ISL. Also inspect ISL and SMC area for any signs of corrosion

 

[shlom]

i have no u5110 on this boardview or schematic for 820-3332

on u7000
pin 1 = 0.028v
pin 2 = 16.41v
pin 3 = 1.51v
pin 19 = 5.39v
pin 20 = 5.43v
pin 9 = 0.033v
pin 15 = 0.060v
pin 27 = 0.031v
pin 28 = 0.032v


resistance between pin 17 and 18 of the isl (u7000) is 4.1 ohm
resistance between pin 27 and 28 of the isl (u7000) is 0.8 ohm

pin 27 28 seems voltage is low and also resistance? meaning a short?

both smc and isl area are very clean, no corrosion...

 

[shlom]

ok after some more measuring
r7021 and r7022 reading o.l and 37k ohms

bad resistors? need to go along with the isl or just those?

could make sense that this the problem?

btw, the reason for not having green light is probably because the dc in board.
couldn't get another dc in board but checked on another board and also no green light there..

thanks...

 

[JohnB8812]

First USE known good DC in board. If both of those are reading that high, they are blown and need to be replaced. Remeasure between pins 27 and 28 and make sure it's a high resistance. If it's 0.8 ohms, then the ISL could be shorting the lines to ground or C7020/21/22 could be shorting it to ground. There is also a chance the traces are blown between them and the ISL or them and R7020. Check traces and replace resistors.

 

[2informaticos]

"pin 3 = 1.51v"
That is very bad; ACIN should jave aprox 4V.

Check R7010 and C7011, U7000 is the last option...

 

[shlom]

ok so after replacing r7021 and r7022 with good ones from another board
i plugged it in and instantly they blown and went bad again..

i pulled everything on the line between pins 27 and 28 and the short was still there
so finally it was clear, the ISL is bad!
i replaced the ISL with a new one, put all the original caps back and two "new" resistors.

after measuring to make sure the short is gone
i plugged it in, ppbus_g3h is 12.61 and..
the board now works like a charm..

solved!

thank you very much !