820-3437-B No charge light PP3V42 present

posarah

Member
Hi all,

i bought another donor board off eBay to have a look at last week. 3437 which has no PP3V42 or PPbus shorts. In fact PP3V42 is present but I’m not getting a green light on the charger. There is sever corrosion on C3740, R3741 and R3742. U3740 looks ok though but I’ll probably replace it to be safe. Issue is both pads for C3740 and r3742 and one pad for r3741 are completely gone and R3742 is now reading ground on both ends.

I saw a slight amount of corrosion on pin 8 of U7100 but upon removal it seems fine so I’m hoping that was just surface junk.

Question is can the board boot without the above 3 mentioned pads intact? I’m not fussed about internal ssd I can always use a USB dock but I’m not sure if those are going to be required for boot or not. Unfortunately I do not have any donor boards to substitute these parts so it’s back to the Ali express waiting game.

thanks!
 

2informaticos

Administrator
Staff member
"R3742 is now reading ground on both ends."
Remove U3740 and check if short disappears.
However, it is not important in the power on sequence; unless U3740 doesn't short 3V42_G3H to ground.

Post basic voltages of U7100; pins 1, 2, 3, 9, 12, 13, 14, 15, 17, 19, 20, 27.
 

posarah

Member
Thanks. R3742 still reads ground on both sides after removing U3740. Pin 1 on U3740 is slightly corroded but otherwise looks fine. I've left it off theboard for now.
ISL Pin readings with a donor installed:
pin 1: 15.27, pin 2: 16.22, pin 3: 16.15, pin 9: 0, pin 12: 3.42, pin 13: 3.37, pin 14: 0.02, pin 15: 0.046, pin 17: 0, pin 19:0 , pin 20: 0, pin 27: 0.391
 

2informaticos

Administrator
Staff member
"pin 3: 16.15"
There is a problem; probably open (corroded) R7111.
Check all resistors and traces around U7100.
Be sure no corroded caps; pay atention to C7100/01.
 

posarah

Member
Is there a way to tell if a dc in board is good or not? Besides trying a known working board as I don’t have one. I unfortunately don’t have any other dc in boards nor do I have a working board to test this one on. Looks clean. Tried to find a board view for the dc in board but it looks like they are not available yet, and the ones that are look completely different. We’re getting 3v42 but i don’t think that means the dc in boards 100% working.
 

2informaticos

Administrator
Staff member
I asked to do something on the MLB.
Why do you concern about DCIN board at this moment?
You must get correct PPBUS_G3H even without LIO flex.

Fix the problems in U7100 area first!!!
 

posarah

Member
Because I haven’t done much of this so I have no idea what can cause what? I was just asking if the dc in board could be giving me what I’m seeing.

Ok now pin 3 on the ISL is 4.3V. R7110 and R7111 had some ugly joints so I've touched it up. Both and the cap are reading as they should and do not look damaged.All components are present and look physically ok bar R7102 which is noted as no stuff in the schematic. Diode measurements for c7101 .448 c100 .447 Though if i connect the charger there getting no voltage. C7142 isn’t reading short but it’s not getting any voltage.
 

posarah

Member
Ok I've remeasured this time at the corresponding components rather than the pins of U7100. See below:
pin 2 use C7105: 15.15V
Pin 3 use R7111: 4.32V
Pin 9 use R5431: 0.030V
Pin 12 use C7102: 3.42V
Pin 13 use R7100: 3.38V
Pin 14 use R5187: 0V
Pin 15 use R5422 0.047:
Pin 17 Use C7150: 0V
Pin 19 use R7101: 5.08V
Pin 20 use R7101: 5.08V
pin 27 use C7120: 0.0206V

All the small resistor/caps around the SMC look ok as well as does the SMC, so they should not be pulling down the lines the SMC shares with the ISL.
 

posarah

Member
Sorry just didn't paste it. Pin 1 is 15.31V. Is 4.32 too high for pin 3? According to Logiwiki their example had pin 3 as 3.81 and the threshold minimum is 3.2 so I'm thinking 4.32 is too high but than checking all the components on PPDCIN_G3H_ISOL which controls that line are matching their values so I'm puzzled as to why it's so high. I also tried removing F7140 and checking which side if any are short, but the CPU side is in the millions of ohms and the other side is in the K of ohms range. Diode modes were .7 and .18 respectively. Injecting voltage revealed nothing really, the caps on that line got slightly warm but only very mildly and they read non short so seem fine.
 

2informaticos

Administrator
Staff member
"the CPU side is in the millions of ohms and the other side is in the K of ohms range. Diode modes were .7 and .18 respectively"
Can you explain this?
Where do you get mohm to ground, if diode mode is 0.180, or 0.700???

STOP to inject voltage into PPBUS_G3H in such manner!!!
Read the forum and will understand why.
 

posarah

Member
Pin 1 with the fuse removed is .1117 & pin 2 is .453 Pin one resistance is reading all over the place, it starts at Millions than dips down to 30K than resets starts at 10K and goes up to 32K than rinse and repeat. I think I need to replace this meter I'm constantly having to change the battery to get it to read values that make sense.
 

2informaticos

Administrator
Staff member
Diode mode readings look good; why do you need to check in ohm mode???
Only switch to ohm mode for very low readings in diode mode, as 0.010 for exmaple.

Pin 1 voltage is bad; should be 0V.
Change U7100 and be sure to have good solders and traces.
Also check resistance between its pins 17/18 and 27/28.
 

posarah

Member
Ok fair enough. I’ve had a lot more experience with resistance values than diode mode hence why I was referencing both as I wasn’t exactly sure whether .1 would be considered low or not, but I do know that K ohms usually is normal operation.

ok I tried re installing u7100 to make sure it’s soldered properly but no change. I’ll have to order one as the one on there now is off a donor board. I’ll re install the original one first see if values change or not than I’ll order a new one if needed.
 

2informaticos

Administrator
Staff member
Be aware, if you talk about 0.1(100 mOhm) in Ohm scale, that means pure short; unless you specify, KOhm, or MOhm as unit.
0.1 (0.100) in diode mode, is totally different thing; could be 100-200 Ohm in resistance mode, depending of multimeter used.
 

posarah

Member
Thanks for the clarification. Not sure if this is relevant or not but I removed the donor ISL and measured it's pins 17 to 18 and 27 to 28 and there 4.8 ohm on the donor ISL. All the measurements previously provided were from this donor ISL. I then did the same on the original ISL the board came with and that's 4.6 for pin 17 to pin 18 & 4.71 on pins 27 to 28. I'm reinstalling this ISL now and will check pin one hopefully it will now be zero otherwise I'll have to wait for a new one to arrive. I had a quick google hoping someones posted the pin measurements on a known working ISL but unfortunately couldn't find anything.
 

posarah

Member
I've reinstalled the original ISL and now pin 1 is resetting. First time you put your probes on it it's .5V than climbs to 1 than 2 than 11 than 15 and resets. Doesn't look like it's the ISL, it looks like it's trying to do it's job but somethings resetting it or it's resetting itself because it's faulty.
 

posarah

Member
Yay I'm finally getting somewhere. Just noticed pin 2 on the ISL was only 4.2V. Checked R7105 and it was in the K ohm range when it's suppose to be 20 ohm. Replaced it, confirmed it's is now 20 ohm and pin 2 is back to 15.15V and pin 1 is now 0.004V so it looks like the ISL is finally working and pulling down CHGR_AGATE. PPBUS_G3H at the fuse is now a happy 8.56V. PP5V_S5 is 5.15V so now I just need to go down the list and see what's missing. Curious what happened to R7105, as it was not originally blown and as you can see above pin 2 was originally 15.5V as it is now and back then I was missing PPBUS and also PP5V_S5. I guess the donor ISL was faulty indeed and replacing it with the original overheated R7105 or something.
 

posarah

Member
Is PP3V3_S4SW_SNS a required rail for the board to post? It's 0v and not short. A lot of the items on that rail are not installed on the board like the camera area and the current sense area. U5440 for example and it's surrounding components. According to the schematic there critical but checking my 3437 and 165 donor boards there also missing them so I'm thinking their no stuff despite not being labeled as such and labeled critical instead.
 
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