820-00165 intermittent boot.

computers history is unknown but. no signs of liquid damage anywhere.

cpu vcore is unstable will alternate between 1.7 and 3.8. sometimes it will dip to like 0.1 mV or 0v.

most of the time the computer wont start and the cpu vcore voltage will just alternate.

sometimes i get no fan spin. while the cpu is alternating

sometimes i get quarter fan spin. while the cpu is alternating

sometimes it will boot up but very slowly.

sometimes fan spin but it will just sit there with a black screen.

sometimes computer will power up fine and boot into the OS and will pass apple ASD.

computer also takes a long time to chime. about 5 seconds assuming it even boots.

behavior is the same regardless of if the motherboard is inside the case or not. or its on AC or battery.
 

2informaticos

Administrator
Staff member
I don't think VCORE goes up to 3.8V, if board still works sometime.

Try few times PRAM reset.
New BIOS, with clean ME, just in case.

Does it start in SMC bypass mode?
 
Sorry I'm not familiar with flashing a new bios for macbooks. you mentioned medusa 2 in a few other posts for bios related issues. I'm assuming that this is the correct tool for it? would i need any other tools for this process?
 

Inwerp

New member
You should put your probe on the cpu side of the inductor. The reason you're reading 0.1...3.8v is that you're reading output of the buck converter which is basically a sqare wave with a pulse width proportional to voltage.
As for random start behaviour, you need an oscilloscope to check all frequency generators. If you don't, you can still check them with a heat gun - usually defect crystal work better when heated to somewhere 100c. Don't do it too much, just check if it makes any difference.
 

2informaticos

Administrator
Staff member
Medusa helps to modify BIOS onboard.
But you can pull out the chip and flash it with classic BIOS programmer.
Check first U1900 and U1950 areas...
 
took a second look at U1950 and there was some very slight corrosion on pin 1 and 8. removed it and cleaned the rust on the pad/chip then resoldered the chip. now it powers on consistently. still need to do further testing. thanks for your help!


before when i was posting the cpu voltage i was measuring pin 2 on L7320 and the voltage was alternating between 0.1 and 3.8. i tried measuring pin 2 of r7320 and i got the same. assuming the machine wont startup.

for future reference ppvcc_s0_cpu is the correct voltage to measure for the cpu right?
 

2informaticos

Administrator
Staff member
Always check voltage on the capacitor connected to the coil.
There is the DC output of the buck-converter.
The other pin of the coil has AC pulses and DMM will just integrate them and shows almost same value as in the DC pin.
However, a little difference between both readings exists.
 
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