So, I got a 820-00597 logic board to replace the one in a 2017 21.5 4K iMac. It worked fine when I got it, powered up fine, was able to install MacOS on it. All done on the bench of course. I decided before putting it in the chassis to reapply the thermal paste for the CPU and GPU and look over the board to make sure there weren't any issues. I noticed a cap had been pulled up off the board (still attached on one side) and soldered it back in place. It was part of the Ethernet circuit, I can look up the specific one if it's important. I also decided to swap the EFI rom chip from the original board so the serial number would match. I had done it several times before on other boards with no issues. After these several steps, I put everything back together and the logic board won't power on. It draws ~ 0.1Amps when power is applied, drops to 0.08 amps then stays there. Strange thing is, if I short the power pads the logic board will act like it is powering off, dropping to 0.03 amps drawn. If I then short the power pads it will go back up to 0.1 amps and do the same thing again. I checked that PPBUS_G3H is being generated. Also diagnostic LED 1 stays solid, it doesn't flicker. None of the other LEDs come on. Anyway, just wanted to see if anyone had any idea what might have happened to it. I wanted to get this board working again because it's got the Radeon 560 4GB graphics.
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iMac 2017 21.5 820-00597 Logic Board Will Not Power On
- Thread starter ideachief
- Start date
"I also decided to swap the EFI rom chip from the original board so the serial number would match. I had done it several times before on other boards with no issues."
Did you ever concern about ME region?
How do you think the PCH will feel with incorrect ME region?
STOP doing that.
Change the serial number manually with HxD and fix the Fsys checksum; videos available on Internet (even on this forum).
Or clean ME region in the old BIOS chip.
Where did you find PPBUS_G3H in this MLB?
Did you try disconnecting CMOS cell?
Can you tell us in schematic, which was the unsoldered cap?
Do you get PP12V_S0_FET?
Did you ever concern about ME region?
How do you think the PCH will feel with incorrect ME region?
STOP doing that.
Change the serial number manually with HxD and fix the Fsys checksum; videos available on Internet (even on this forum).
Or clean ME region in the old BIOS chip.
Where did you find PPBUS_G3H in this MLB?
Did you try disconnecting CMOS cell?
Can you tell us in schematic, which was the unsoldered cap?
Do you get PP12V_S0_FET?
Ok, I will take your advice regarding the BIOS chip.
There is no PPBUS_G3H on this iMac board. I think the equivelant P3V3_G3H. On C6922 I get 3.7V. On U6970 I get 3.8V on PIN 8, P3V3_S5. Pin 7 which is
FET_EN_P12V_S5, I read 23.17V, which is obviously not good. All other values on U6970 and U6920 are nominal.
I've tried without the CMOS cell. The cap that got detached was C4003.
Again, thanks.
There is no PPBUS_G3H on this iMac board. I think the equivelant P3V3_G3H. On C6922 I get 3.7V. On U6970 I get 3.8V on PIN 8, P3V3_S5. Pin 7 which is
FET_EN_P12V_S5, I read 23.17V, which is obviously not good. All other values on U6970 and U6920 are nominal.
I've tried without the CMOS cell. The cap that got detached was C4003.
Again, thanks.
"Pin 7 which is FET_EN_P12V_S5, I read 23.17V, which is obviously not good."
Why do you think that?
Don't make wrong assumption so easy, try to understand a schematic first.
You can't make any relation between actual 3V3_G3H and PPBUS_G3H from a Macbook.
BTW, you can check 3V3_G3H at L6930/C6932 (not C6922).
"Also diagnostic LED 1 stays solid, it doesn't flicker"
So 12V_S5 must be there.
That's the reason nobody asked about U/Q6970.
Q8450 also needs more than 20V on its Gate to work properly.
Trigger SMC_ONOFF_L and check for drop pulse (3V->0V->3V) at PM_PWRBTN_L (at same time).
If detected, you should catch a pulse at PM_SLP_S4_L and PM_EN_FET_P12V_S0 too; check at same time with trigger event.
Use J5120 pads instead of power button.
C4003 is not critical and you can leave it unsoldered without problems.
Why do you think that?
Don't make wrong assumption so easy, try to understand a schematic first.
You can't make any relation between actual 3V3_G3H and PPBUS_G3H from a Macbook.
BTW, you can check 3V3_G3H at L6930/C6932 (not C6922).
"Also diagnostic LED 1 stays solid, it doesn't flicker"
So 12V_S5 must be there.
That's the reason nobody asked about U/Q6970.
Q8450 also needs more than 20V on its Gate to work properly.
Trigger SMC_ONOFF_L and check for drop pulse (3V->0V->3V) at PM_PWRBTN_L (at same time).
If detected, you should catch a pulse at PM_SLP_S4_L and PM_EN_FET_P12V_S0 too; check at same time with trigger event.
Use J5120 pads instead of power button.
C4003 is not critical and you can leave it unsoldered without problems.
I see the voltage drop on PM_PWRBTN_L when triggering SMC_ONOFF_L, 3.3V -> 0V -> 3.3V (using J5120). PM_SLP_S4_L stays at 3.3V when triggering SMC_ONOFF_L, unless I short it (at J5120) until the board turns off, then it drops to 0V. PM_EN_FET_P12V_S0 stays at 0V during all of this. I measured these voltages at the respective test points.
So you have stable 3V at PM_SLP_S4_L when charger is connected?
That means PCH already started power on sequence; no need to trigger SMC_ONOFF_L.
Check PM_SLP_S3_L level too.
Do you get voltage at L7650 and L7310?
That means PCH already started power on sequence; no need to trigger SMC_ONOFF_L.
Check PM_SLP_S3_L level too.
Do you get voltage at L7650 and L7310?
If I measure PM_EN_FET_P12V_S0 to ground I get about 240 Ohm. So if I measure the voltage to PP12V_G3H on U8450 I get ~12V, which stays steady if I short J5120.
Yes, I agree that I need assistance in understanding schematics. If you have any suggestions on a guide that would help me, I would appreciate it.
Yes, I agree that I need assistance in understanding schematics. If you have any suggestions on a guide that would help me, I would appreciate it.
"L7310 is at ~5V to L7650"
No idea what you've meant.
I hope you don't have 5V at L7310.
Correct voltage is explained on page 63; Vout=1.8*(Rb/(Ra+Rb)), with Ra/b marked on the schematic (R7330/31).
In other words, 1.2V for DDR4 type.
"If I measure PM_EN_FET_P12V_S0 to ground I get about 240 Ohm"
Nobody asked about ohm resistance there.
Be patient, you will understand schematics in time.
Just don't waste time with irrelevant checkings.
Post U8500 voltages (pins 8, 9, 10, 14), when both PM_SLP_S4/3_L are present.
No idea what you've meant.
I hope you don't have 5V at L7310.
Correct voltage is explained on page 63; Vout=1.8*(Rb/(Ra+Rb)), with Ra/b marked on the schematic (R7330/31).
In other words, 1.2V for DDR4 type.
"If I measure PM_EN_FET_P12V_S0 to ground I get about 240 Ohm"
Nobody asked about ohm resistance there.
Be patient, you will understand schematics in time.
Just don't waste time with irrelevant checkings.
Post U8500 voltages (pins 8, 9, 10, 14), when both PM_SLP_S4/3_L are present.
"all measured to ground"
Nobody expects to measure voltage in other way.
"Pin 10: 0.013V"
Don't you get L7310 voltage?
You've said PM_SLP_S4_L is high.
Post U8500 pins 1 to 6 voltages too.
Also check U7350 and U8410 output voltage.
Nobody expects to measure voltage in other way.
"Pin 10: 0.013V"
Don't you get L7310 voltage?
You've said PM_SLP_S4_L is high.
Post U8500 pins 1 to 6 voltages too.
Also check U7350 and U8410 output voltage.
U8500 Voltages: Pin 1: 3.324V, Pin 2: 1.00V, Pin 3: 0.00V, Pin 4: 3.324V, Pin 5: 0.016V. Pin 6: 0.00V
U7350 Voltage Out (Pin 1 & 2): 0V
U8410 Voltage Out (Pin 8): 1.00V
I can't see why U8500 Pin 10 and L7310 should have the same voltage, but the readings are the same: U8500 Pin 10: 0.013V, L7310 Pin 1 & 2: 0.048V
U7350 Voltage Out (Pin 1 & 2): 0V
U8410 Voltage Out (Pin 8): 1.00V
I can't see why U8500 Pin 10 and L7310 should have the same voltage, but the readings are the same: U8500 Pin 10: 0.013V, L7310 Pin 1 & 2: 0.048V
"I can't see why U8500 Pin 10 and L7310 should have the same voltage"
Who said that?
Don't make assumptions based on wrong suppositions.
Output voltage is not same as its power good, but directly related.
"Pin 2: 1.00V"
Are you sure about this?
Is not good voltage; should be 3.3V, check it again.
If really bad, then check R8410/11, which one is there.
Who said that?
Don't make assumptions based on wrong suppositions.
Output voltage is not same as its power good, but directly related.
"Pin 2: 1.00V"
Are you sure about this?
Is not good voltage; should be 3.3V, check it again.
If really bad, then check R8410/11, which one is there.
PM_PGOOD_FET_P1V0_S3 is pulled high to 3.3V; did you check which resistor is mounted there?
Ok, hopefully we're looking at the same schematic. Pin 2 on U8500 is fed off U8410 Pin 7. There is a 10K resistor, R8410, with PP3V3_S5_PWRCTL on one side and PM_PGOOD_FET_P1V0_S3 on the other. Both voltages are nominal: 3.3V for PP3V3_S5_PWRCTL on R8410 Pin 1 and 1.0V for PM_PGOOD_FET_P1V0_S3 on R8410 Pin 2.