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820-3437 no video (vcore present)

ytesfay80

ytesfay80

Member
This board was damaged from coffee spill. Initially the only thing that would happen when the charger was plugged in was a light on the charger.
I wrote down the components that were damaged before fluxing and heating the areas.

q7130
c7621
removed u1950 and pad for 3v42 was gone. scraped a little and brought it back
u8160
replaced u5110
replaced c7137
removed corroded j6100 and cleaned pads

After cleaning those areas the fan turns on and CPU VCore is around 1.69v. I plugged in the trackpad cable, screen cable and ssd and I don't hear a chime nor do I see anything on the screen even with a flashlight. I have no voltage on backlight output.
SMBUS_SMC_0_S0_SCL - 0v
SMBUS_SMC_0_S0_SDA - 0v
PPBUS_G3H - 8.57v
U8300 (Pin 1 - EDP_PANEL_PWR) - 0v (I even plugged in a bare lcd with just the lcd cable plugged in and it was still 0v.)

There are no damaged components around the SMC but there are a few probe points that look like they took some liquid damage.
Also, the battery was kind of hard to pull out and it looks like it had some damage to it but I did all these measurements without the battery plugged in.
 
Last edited:
larossmann

larossmann

Administrator
Staff member
remove battery and charger power. keep battery unplugged, then plug in the charger.

does this do the thing where the fan spins, stops, spins, stops, spins, stops, then spins and it turns on?

or does it just turn right on?
 
ytesfay80

ytesfay80

Member
Yes. The clock area(u1950) was corroded. I removed it and scraped the 3v42 pad to bring the trace back and put another chip on there.
I already removed the JTAG (J6100) and cleaned the pads.
 
ytesfay80

ytesfay80

Member
I measured the resistance on the resistors on the SPI BUS Series page and they measured and looked fine(R6114-7, R6110-3, R6120-3, R6125-8).

How do I check the traces from u6100 to CPU/SMC

I checked the traces from each pin of U6100 to the probe point next to them and there was continuity. Also every pin of U6100 was from 3.28v-3.31v except for pin 4(ground)
 
ytesfay80

ytesfay80

Member
There was no corrosion around the U6100/U1900 area but there was some probe points that were discolored(around Probe 825) as if there was some liquid damage there. Same thing with the SMC. There was no corrosion around it but there are some discolored probe points(the top of the SMC around Probe 949/995).

Should I try reflowing the SMC first?
 
ytesfay80

ytesfay80

Member
I was going to reflow the SMC and if that didnt work I would pull the SMC and check traces.

Before that though do you think U6100 could be the issue? Should try pulling it?
 
ytesfay80

ytesfay80

Member
I don't have a reader for the chip so I will have to just keep the original. Do I just replace it with one from a donor and see if it boots or do I just pull it and clean the pads because I thought macbooks don't run properly anymore once you change the spi rom chip.
 
ytesfay80

ytesfay80

Member
No Title

Okay I swapped the bios chip and now the fan spins for about 1-2 seconds then the fan just stops spinning. I took the bios chip from from another 820-3437-B but for some reason the chip had a different marking on the top of the chip. I took a picture of them side by side(original on the left).
 

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dukefawks

Administrator
Just a different brand chip. Did this chip come from a China board? They are sometimes erased, so you need to check on the programmer.
 
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