[FUBAR] LB 820-2879 B no green or orange light (needs SMC)

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Crizz

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If you don't have a powerful hot air station it is a good idea to preheat the board.
You can build yourself a Teppan-Yaki preheater :D
Here is a photo from 2011:
 

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Mac-N-Sauce

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ok louis, replaced everything and now down to .7v on charging circuit. So whatever i am doing is effecting only that 12v rail. I pulled the isl off another board. It had no visible damage around it.
So I have replaced it three times now. Two new ones and the last one used. I checked the ISL from the sides to see pin connections and it looked good.

Any, thought? Do i just keep killing the ISL?
 

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Mac-N-Sauce

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OK, so i figured out that the common denominator was the ISL. So I changed it once again and actually soldered it correctly. Fourth time is the charm.. I now have 12.56 v!!!!!! However, I still can not short power pads for fan spin and charger does not go orange with battery plugged in. I am attaching a photo of the final ISL solder job. I realized that I had heat way too high and I was not getting it just right on the pads.
 

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Mac-N-Sauce

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Anyone got any other thoughts? I feel like I might be missing something simple. I have checked current sensing, etc. Seems like SmC is just saying no somewhere
 

aprendiz

Moderator
ok, now you have 12.56V right? if yes, do you have PP3V3_S5_REG? and for no orange light (charge) what voltage do you have on pins 4 and 6 from J6950?
 

Mac-N-Sauce

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I am trying to understand the flow of the circuit with the u7200 chip. i don't have the 5v3v3 reg en on pin13, which appears to come from SMC?
 

Mac-N-Sauce

New member
Resistor measures good, pin 1 on U7840 is 3.4v, SMC_RESET_L is 3.4v on pin 13 of U7000. I have no visible signs of damage around the U7200 but would you recommend replacing U7200 anyway? Is there some way to test if it is good?
 

larossmann

Administrator
Staff member
SMC_PM_G2_EN creates PP5V_S5 by telling U7200 on pin 13 to turn on PP5V_S5. Do you have PP5V_S5? If you do, pin 13 can go away.

Check for a short to ground on PP3V3_S5. If no short to ground, remove Q7221 and tell me if PP3V3_S5 comes up.
 

larossmann

Administrator
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Q7221 is related to a different rail. If SMC_PM_G2_EN is not fluctuating, but PP5V_S5 is fluctuating, it's a safe bet your issue is either with U7200(likely) or U7840(less likely, but still possible). You have green light to replace U7200! Bonus points if you don't burn the fan or speaker connector.
 

Mac-N-Sauce

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Supported your site. I really appreciate what you are doing. you guys are awesome! I know I am a pita right now, but I will get better! :eek:
 

larossmann

Administrator
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Is there a short to ground on PP5V_S5? Is SMC_PM_G2_EN fluctuating? My prior post said "if SMC_PM_G2_EN is not fluctuating", I trust you checked that!
 

Mac-N-Sauce

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Ok, screwed that up. SMC_PM_G2_EN in diode mode measures .023v not fluctuating, PP5V_S5_LDO is fluctuating at .361-.4v in diode mode so it looks like they are shorted to ground.
When I check these points on a working board in diode mode i get OL
 

larossmann

Administrator
Staff member
1) 0.36 to 0.4v in diode mode is not shorted to ground
2) Please for the love of god tell me you are not making diode mode measurements with power going through the board
3) I asked if SMC_PM_G2_EN voltage is fluctuating. Measure voltage. Is it steady or does it move?
 

Mac-N-Sauce

New member
Ok, they are not shorted, and SMC_PM_G2_EN is fluctuating in mv, and yes i am an idiot!
PP5V_S5_LDO = .53v
SMC_PM_G2_EN = .421v
 

larossmann

Administrator
Staff member
So we're clear, those are DC voltage measurements, and not diode mode measurements, right?

If so, SMC_PM_G2_EN is too low, which points to an SMC issue, U7840 pulling it down, or U7200 pulling it down. At this point since you've already replaced U7200, my guess is bad SMC.
 
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