(347) 552-2258 [email protected]

820-00840 Not turning on

tlough75

tlough75

Member
So a customer of mine bought a sight unseen 820-00840 machine that is not turning on. On my USB-C am meter it is showing 19.8V @ .01mA. I am getting P3V3_G3H but not PPBUS. PPBUS_G3H is reading 1.9 Ohms to GND. I take it that is not good. Also, the only signs of liquid is by the battery.
 
Last edited:
tlough75

tlough75

Member
So after measuring all of the coils to compare with F7000 Pin 2, which is 1.9 Ohms, The following coils have the same reading:
L7410
L7420
L7430
All three measure 1.9 ohms to GND. Could all three of the HSM be shorted? or am I barking up the wrong tree? I do not have a known good board for comparison at the moment.
 
tlough75

tlough75

Member
Are you saying that it could only be one that is short, but causing all three to show short? Ill do a game of eenie meenie miney mo
 
tlough75

tlough75

Member
ok, so when i removed the first HSM, ppbus is not shorted anymore to GND, reading 1.5M ohm to gnd. Is it safe to plug board in with these removed to check ppbus voltage? the other thing Is I only have a 820-00875 as a possible donor. Should I try to get these HSM new or is that impossible? My client will wait if he has to.
 
Last edited:
2informaticos

2informaticos

Administrator
Staff member
Get the chip from donor board.
All the boards 00840/50/75 have the same one.

But be aware, CPU could be already dead; overvoltage on VCCGT rail occured...
 
tlough75

tlough75

Member
Took one from donor 875, computer now showing ? Folder and .625V CPU Vcore. The problem now is the fan is slowly ramping up to high speed, and when I plug in SSD, the progress bar starts moving fast, then stalls at about 90%.
 
tlough75

tlough75

Member
Yeah I cannot seem to get it to run even from a USB stick. when I try to select the drive to boot from I click on my USB vs internal SSD and I get a circle with a slash through it. I tried to run internet recovery and when I try to go to the name of my Wifi, the computer slows way down. one of the times I booted it I got some kind of kernal error but it diisappeared before I could see what it said. What I am wondering is even though I replaced U7430, the CPU might have gotten a small enough zap to render it useless but it still tries to work. I'm just not sure. I am going to keep attempting to either get it to boot from an external OS or get a different SSD.
 
Last edited:
2informaticos

2informaticos

Administrator
Staff member
Remove internal SSD when you try to boot through USB.
Be sure your test OSX is supported by the machine.

Try to start in safe mode, or even SMC bypass; if cannot login other way.
 
tlough75

tlough75

Member
So it still will not boot from USB but I got it to boot into safe mode. Is HW monitor something on in the OS? or do I have to get it?
 
2informaticos

2informaticos

Administrator
Staff member
First of all, try to recover any data, if possible.
Next, do a fresh OS install.

"Is HW monitor something on in the OS? or do I have to get it?"
Find it with Google search.
You will need to diagnose many machines.
 
tlough75

tlough75

Member
Got HW monitor. The following are reading 128 degrees C:
airport proximity
mainboard proximity
heatpipe incoming air
heatpipe outgoing air
 
tlough75

tlough75

Member
So I replaced the TPAD and cable, now the the two heat pipe sensors are reading normal, but the Airport Proximity and the Mainboard proximity still reading 128 degrees C. The board is drawing 2.5A but the fans is spinning normally. The CPU is getting really hot. The fan does not turn on until the CPU is hot to the touch. Is this normal? It still will not boot to internal SSD unless in safe mode.
 
You must log in or register to reply here.
Top