820-4924-A No Backlight....

2click

Member
Hi, so I have this 820-4924-A that its turning on and if I put a flash light on the back of the apple logo, I can see that it is booting.... I'm new to the forum and have checked that the voltages on U7700 are present but the Enable pin. I went to the 8030 and have no voltages there... please Help!....
 

2informaticos

Administrator
Staff member
"voltages on U7700 are present but the Enable pin"
Missing BKLT_EN_R?
I hope you've checked with LCD connected.

"the 8030 and have no voltages there"
Post all voltages of U8030.
 

2click

Member
UPDATE: I connected the LCD and the enable got 3.3v. The voltage divider on Q7700 wasn't working, I replaced the U7700 and now I have image. The only thing is that it gets stuck loading the operative system. Any clue that what could be causing that? Tried to boot from an external drive, waited for around 5 minutes and it didn't finish loading.... the fan goes full speed... and the external hard drive keeps blinking...
 

2informaticos

Administrator
Staff member
"I connected the LCD and the enable got 3.3v."
For the future, remember to measure video related voltages and signals with LCD connected.

Try clean ME BIOS.
Some link should be already posted on the forum.
If you cannot find any, upload your backup.
 

2click

Member
I'm sorry I don't know what you mean with clean ME BIOS. I have another board, same model... should I replace the bios with that one? Where can I make a backup of the bios and how can I load it? I?m sorry but this subject is completely new for me.
 

2informaticos

Administrator
Staff member
Backup means a copy of your original SPI chip (U6100).
You will need to remove it and USB BIOS programmer to read/write; CH341 is probably the cheapest one.
Medusa programmer can do al the job onboard; but is not cheap.
 

2informaticos

Administrator
Staff member
Good enough.
I use it to upload dumps from my PC to Medusa ROM; and save dumps from Medusa, after read from Mac ROM.
You will need to place the chip on adapter to use that programmer.
 

dukefawks

Administrator
ME should not cause the fan to go full speed. Run diagnostics by holding down D and turning on. More suspecting a sensor issue
 
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2click

Member
With the adaptar connected to the PSU and the mac I got this results... the fan stops completely for around 5 seconds almost at the end of the test and goes full speed again (it is all the time when testing).
 

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2informaticos

Administrator
Staff member
As dukefawks mentioned, you have sensor issues.
Check first AVREF_SMC voltage.

Try known good trackpad flex/board.
Be sure to use original 60/85W Magsafe 2 charger, not 1 -> 2 adapter; do you get amber light?
 

2click

Member
It looks pretty good to me... Yes I tried a totall different working computer... can it be the SMC? in the other case the battery doesn't work so the diagnostics said to replace the battery and the same of the trackpad, can I discard the smc? Or should I recball it again? Thanks...
 

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dukefawks

Administrator
Just to make sure here, you used a complete different case with trackpad cable and everything? At least the battery in that one has seen better days but that will not cause the fan to run high.

Check diode mode on both I2C_TPAD_SDA and SCL lines on the trackpad connector.

The trackpad is working normally in the boot screen menu? Fan still goes on full after 20 seconds?
 

2click

Member
Checking the trackpad lines, I had on PP3V3_S4_TPA = 8 v so I went and heated U4830, now I'm getting 3.3v on that line, but still getting the error when loading the system. Tried to boot from an external drive with macOS and when I connected the drive on the selection screen, the image went off. I really don't know what else to do with this board, please help!!
 
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