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Board 820-2914-A no PP3V42_G3H after shortcut

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Daccordo73

New member
Hi,

I made a stupid thing while trying to fix a fan connector issue on a 820-2914-A, shortcutting the PP5V_S0 to ground.

After that I'm sure something blown, because I heard it and I smell it.

Searching with microscope don't show anything damaged, but obviously the board is not working anymore.

I'm trying to troubleshoot it. Actually PP3V42_G3H is not present (I read 0).

PPVIN_G3H_P3V42G3H is present when the charger or the battery are connected (with the charger I read 16,48V).

On pin 8 and 2 of U6990 I can read 3,86V (P3V42G3H_FB), but the output of U6990 is 0.

If a use a multimeter in diode mode on the output (red on ground and black on pin) I read 0,001 so I think I have a shortcut somewhere.

What is the best way to go on? Removing one by one the components on the line to find the one failing on injecting some power to find (I hope) the one heating?

Is the time worth or the shortcut on PP5V_S0 could have destroyed the board?

Thanks
 
2informaticos

2informaticos

Administrator
Staff member
First of all, welcome to the forum!

A simple short on 5V_S0 shouldn't cause such damage.
You are "the lucky guy" in 1000, to happen this.

If you have pure short on 3V42_G3H, voltage injection method will locate the culprit rapidly.
Start with 1V and go up slowly (if needed), no more than 4V.
First, set amp limit of your lab PSU to max.

BTW, I hope you've measured diode mode after removing power.
 
D

Daccordo73

New member
ok, strange things happen here. With voltage injection nothing start heating. But I see, after a while, that the current goes down to a low level. So I check again with diode mode the possible shortcircuit and it was gone :oops::oops:. The only thing that could be happen is that the shortcircuit was completely blown by the voltage injection....

So I try to connect the power supply to the board and I have got 3V42_G3H again, and green led on the power supply connector.

I check some voltage values:

PPVBUS = 12,56V
PP5V_S3 = 4,90V

But the board don't start.

The system is charging the battery because after a while the green led became amber.
 
Last edited:
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Daccordo73

New member
2informaticos said:
Check the voltage on all big coils.
Click to expand...
I will check ASAP

2informaticos said:
The fan spins?
Click to expand...
No. Only a little when I remove power connector.

2informaticos said:
ALL_SYS_PWRGD goes high?
Click to expand...
No

After a while I was able to find a very hot component. Is U4800. Is so hot I can't place a finger over it. I think it is gone. Could be the reason the board don't start? As I can understand is an infrared receiver. Could I remove it and try if the board start?
 
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Daccordo73

New member
Removed, no change.

ALL_SYS_PWRGD don't goes high.

About the coils:
L9710 = 0V
L3895 = 322mV
L7260 = 3,34V
L7720 = 1,81V
L7770 = 1,53V
L7220 = 5,01V
L8920 = 0V
L7550 = 0V
L7510 = 0V
L7520 = 0V
L7530 = 0V
L7030 = 12,55V
L7100 = 0V
L9560 = 1,51V
L7630 = 0V
L9510 = 1,02V
L7330 = 1,5V

I hope I don't miss someone.

System powered only by charger, no battery connected.

One more note: U1800 stay warm, also if the board is not running.

Thanks
 
2informaticos

2informaticos

Administrator
Staff member
Missing 1V05_S0 and VCCSA.
Post U7100 and U7600 voltages.

Also check ohm resistance to ground at L7100 and L7630.
 
D

Daccordo73

New member
U7100
All pin at 0, except 14 (20mV), 15 (3,29V), 20 (5V).

U7600
All pin at 0, except 3 (3,26V), 4 (0,5V), 7 (24mV), 8-10-11-12 (30mV), 13-14 (5V).

L7100 to ground 41,6 Ohm
L7630 tp ground 13 Ohm

Thanks
 
2informaticos

2informaticos

Administrator
Staff member
"U7100
All pin at 0, except 14 (20mV), 15 (3,29V), 20 (5V)."
What about pin 19, surely 0V?
If yes, post diode mode to ground there.
 
D

Daccordo73

New member
I checked again and I can confirm a 0V reading.

Checking in diode mode I have 0,001V, so shorted. I think C7102 shorted. Correct?

Also R7101 seems strange. I read 44 Ohm instead of 2,2 expected from the schematic.

Thanks
 
D

Daccordo73

New member
One step forward....

After replacing U7100 & R7101 on L7100 I can read 0,911V. Should be 1,05V, correct?

But still no voltage on L7630.
 
2informaticos

2informaticos

Administrator
Staff member
0.9V is good; did you look at VID1/0 table?
Don't make wrong assumptions so easy.

Post U7600 voltages; pins 3, 13, 14.
Also check diode mode to ground at L7630.
 
D

Daccordo73

New member
2informaticos said:
0.9V is good; did you look at VID1/0 table?
Don't make wrong assumptions so easy.
Click to expand...
Sorry, I look near L7100 on the schematic and I see Voltage=1.05, I don't see the table at all.

But at least I fixed something. This is good.

2informaticos said:
Post U7600 voltages; pins 3, 13, 14.
Also check diode mode to ground at L7630.
Click to expand...
Pin 3 = 3,26V
Pin 13 and 14 = 5V

L7630 seems shorted to ground (0,005V). I remove it (to understand where the short is) and I remove also R7640, and seems the only pin shorted of R7640 is the number 2, but that pin is connected everywhere.... After the resistor removal no more short (obviously) in L7630.
 
2informaticos

2informaticos

Administrator
Staff member
Doesn't look to be short; compare with good board.

Change U7600 and check its solders, traces and surrounding components.
 
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