820-00281 Bootlooping on right side of the board

JohnB8812

New member
So got an interesting one not sure where to look. I've fixed a few touchbars, but this one came is super clean for no power. Basically the problem is this device has 5 volts on DC in but it bootloops on one side of the board. When you plug in a USB connector to JB500 (left side port) you get 5 volts on DC in with about a 0.04 amp draw. When you plug in a connector to J3300 you get 5 volt bootloop 5 volt bootloop over and over again. Like I said, no evidence of liquid anywhere on the board. I reflowed both U3100 and U3200 just on the off chance they had a broken ball under them, but no change. Where do I look from here? DC in and PP3v3_G3H are both not shorted to ground.
 

2informaticos

Administrator
Staff member
If SMC cannot talk with charger, you only get 5V.
However, U7000 can work with 5V, in boost converter mode (step-up).
Post basic voltages for U7000 and U7800.

As you have different symptoms on the left/right connectors, compare resistance to ground on both sides.
Check LDOs lines of U3100/3200 and UB300/400.
 

JohnB8812

New member
U7000
pin 1 4.96 volts
pin 5 4.67 volts
SMC_BC_AC_OK 3.36 volts
PPDCIN 5.07 volts
PP3v3_G3H: 3.36 volts
HPWR_EN_L: 0 volts
SMBUS lines pulsing 3.3 each (normal)
SMC_RESET_L 3.3
pin 27 4.96 volts

U7800
All voltages going into U7800 are 0. Banjo NOT getting hot.

When you say resistance to ground do you mean on DC in?

All LDO lines good on UB300 and UB400 3.3 1.8 1.1 etc.

PP3v3_G3H, PP3v3_UPC LDO, PP1v8 LDO, all LDO's pulse between 0 and their correct value when it bootloops.
PP20v_USBC_XB_VBUS is ZERO volts on C3201 but pulses from 5 to 0 on C3101.

I think my problem is definitely no PP20v_USBC_XB_VBUS for U3200?
 

JohnB8812

New member
Ok replaced Q3200 now I only get bootlooping on the top USBC port. The bottom one closest to U3200 no longer bootloops. ONLY the top one.

Nevermind both are still looping. Freeze spray appears to keep them from bootlooping, so maybe something get cooled off is stopping it?
 
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JohnB8812

New member
Any other ideas on this? I know it's a new POS, but just a need a little direction on it. Wish I could find obvious liquid to figure it out, but no obvious liquid anywhere
 

2informaticos

Administrator
Staff member
I do not understand your notations for U7000, it is BGA...
Do you get voltage at F7000/1?
Resistance to ground there?

Compare U3100/200 and UB300/400 in diode mode for power rails.

U7800 gets 5V like R7020 too.
And should generate some voltages, page 70.
 

JohnB8812

New member
Ok back to this one
I have 0 volts on both sides of F7000/1. Guessing that's because of 5 volts on DC in.
I have roughly 5 million ohms on both sides of the two, so no shorts on either side.


With my measurements on U7800, they were taken on components near it. No liquid in that area. Zero volts at R7020 and it is not blown.

I think I found the problem. Diode mode PP3v3_G3H is very low near UB300. I put voltage through and there's a partial short under UB300. That sucks
 

JohnB8812

New member
It does indeed. Also when removing it the diode mode measurement went to matching the others. Now for finding this chip lmao I don't wanna reball it, but I'm prob gonna have to lol
 

2informaticos

Administrator
Staff member
U7000 is prepaired to work on boost converter mode (step-up).
So check some of its voltages...
Also check basic voltages (LDO, RTC) for U7800.
 

2informaticos

Administrator
Staff member
Is not a bad idea.
Whitout UB300, charger only delivers 5V, even if the rest of the board is OK.
I hope it doesn't have firmware...
 

JohnB8812

New member
Yep it does have firmware have to get the exact CD3215C00 chip and reball it lol luckily I found a stencil so should make it easier. Thank you for all the help so far I do appreciate it!! Going to replace that guy then will get back to you
 

JohnB8812

New member
Ok so BIG news on these...l replaced the CD3215C00 and now the device is powering on!!! However, the port for the CD3215C00 I replaced is not working lol. I think it may be related to the chip I replaced. I'm going to go ahead and try another chip to rule that out. I do know that possibly now the board will function if one of the IC's is not quite good, but not fully dead. But we will find out soon
 

JohnB8812

New member
Ok so here's the verdict...with a good well soldered IC, all four ports work and the device is fixed!!!!

Things to take away from anyone who comes across these issues in the future.

1. Make sure your charge IC's are good when you pull them (tough to do)
2. These devices CAN turn on with one charge IC not working properly (has to be a good IC if it was improperly soldered)
3. Improper soldering will allow the device to kick on but the port for the one that is not soldered properly will NOT allow the port to work.
4. Bootlooping is not necessarily on the port side of the bootlooping. In this case, a charge IC on the non bootlooping side was causing bootlooping on the other side.

Thank you for all the help 2informaticos!
 

2informaticos

Administrator
Staff member
Good to hear that.
Just a mention, CD3215C00 is not charge IC; that is U7000.
CD3215C00 is an USB port controller; but each controls one input MOSFET.
 

JohnB8812

New member
Gotcha I’m just used to calling them charge ICs but basically the USBC controllers are a pain but they will fix the problem!
 
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