820-00850 5V 36ma no liquid, no DFU

[raainxx]

Hi,
this board 820-00850 is lock to 5V 36ma (no liquid spill, no DFU).
i have PPBUS = 12,29V, PP3V3_G3H = 2,5V to 3,3V no fix.
i inspect the board in microscope, I don't see a short.
Big coil seems ok except L7270= 0,010 & L8102=0,065 in diode mode
can you help me please?
thanks

 

[2informaticos]

Did you test the board alone on the desk?
Also test with both charger and battery connected.

3V3_G3H must be steady.
What is diode mode to ground value?
Be sure all R6993/5/6/7 have correct ohm values.
Also check R6999 to be 0 ohm.

 

[raainxx]

Yes I try the board alone, same problem with no fix signal 3V3_G3H. diode mode = 0,4V
i don't find R6993 and the other. why? are you sur?

 

[2informaticos]

Mentioned resistors set L6995 output voltage.
Did you look at page 52 (U6990)?

 

[raainxx]

Sorry the board is 820-00850 :-(

 

[2informaticos]

Confirm if you reffer to L7660, or L6900/1, please.

 

[raainxx]

L7660 = 3V3_G3H

 

[2informaticos]

Check all components and traces related with L/U7660 and corresponding side of U7650.

Post U7650 voltages; pins 23, 22, 12, 13, 29, 21.
Tell us if any fluctuates.

 

[raainxx]

12=0V
13=0V
21=0V
22=3,293V fix
23=12,29V fix
29=0v
i remove L7660 to see if P3V3_G3H is stable but always same (not fix)

 

[2informaticos]

You shouldn't have voltage at all on L7660, without enable (pin 21).
Just in case, change U7660.

 

[raainxx]

i find a little hole on U7800, C7908 seems remove (maybe a shortcut).
is it possible to change U7800?

 

[2informaticos]

Yes, you can get it from other scrap board.

 

[raainxx]

ok thanks, I change U7800 and now the PP3V3_G3H is stable.
the pin 277 under U7800 was burn. now work well, thanks