[820-4924-A] When does testing require LB in case?

Holes Flow

New member
Experts,

I have a purchased 820-4924-A, and it seems all my S5 voltages are there. But I'm working on the LB au naturel. I don't expect fan spin because the CPU is not turning on (heating up). The whole board is cool...

It isn't going to S4, so my question is: Is this the point where I need to drop it in the case and connect it?

TIA!
 

2informaticos

Administrator
Staff member
The fan of this board only starts to spin when CPU gets hot.
It spins from first moment if is turned on in SMC bypass mode.

No need to place the board on the shell.
You can ceck for USB activity, being the most used test.
If no S3 voltages present, board doesn't turn on; no reason for further tests.

Use original 60/85W Magsafe 2 charger.
Tell us if you get 3V3_S5/SUS at least.
 

Holes Flow

New member
Thanks for the reply & guidance, @2informaticos.

A. PP3V3_S5
on p. 58/82, U7501 page:
PP3V3_S5_REG = 3.3V measured at pin 1 (output side) of L7560:
1655062697996.png

B. PP3V3_SUS was a little harder to track down, with some OK, and some no voltage:

-PP3V3_SUS_ROM = 3.3V (pg.47, C6101, pin 1, which is VCC to U6100 & U6101).
-PP3V3_SUS_P3V3SUSFET = 0V (pg.63, C8020, pin 1, which is VIN to "3.3V SUS Switch" U8020)
-PP3V3_SUS_FET_R = 3.3V (VOUT pin of "3.3V SUS Switch" U8020)
...this implies P3V3SUS_EN = 3.3V, which it was/is.
On U8130 "3.3V SUS Detect" (pg.64 "Power Control"):
-PP3V3_S5_PWRCTL = 3.3V (VDD to U8130)
-PP3V3_SUS_PWRCTL = 3.3V ("SENSE" on 8130)
Just below U8130, "SUS Enables":
-P3V3SUS_EN = 3.3V

I'll keep looking for more PP3V3_SUS* that have 0V, going down the bus list on pg.68

Thanks!

P.S. I really appreciate the help, as too many circuit traces dead end where components on the schematic aren't on the board! (Secret No-Stuff?)
 
Last edited:

Holes Flow

New member
Going down the PP3V3_SUS busses on pg.68:

PP3V3_SUS_PCH_VCCSUS_GPIO = 3.3V
PP3V3_SUS_PCH_VCCSUS_ICC = <can't measure>
PP3V3_SUS_PCH_VCC_SPI = 3.3V
PP3V3_SUS_PWRCTL = 3.3V
PP3V3_SUS_P1V05SUSLDO = 3.3V
(U7840 "SUS LDO" putting out 1V on PP1V05 _SUS_LDO = OK)
PP3V3_SUS_PCH_GPIO = 3.3V
PP3V3_SUS_PCH_VCCSUS_RTC = 3.3V
 

2informaticos

Administrator
Staff member
Do you really expect to get different reading on the same power rail???
Impossible, unless you have a broken trace.
Don't waste your time in such manner.

BTW, is better to check DC voltage on the output pin of the coils from buck-converters.

So, if no voltage at L7520, trigger SMC_ONOFF_L and check for pulse there (at same time).

"-PP3V3_SUS_P3V3SUSFET = 0V (pg.63, C8020, pin 1, which is VIN to "3.3V SUS Switch" U8020)
-PP3V3_SUS_FET_R = 3.3V (VOUT pin of "3.3V SUS Switch" U8020)"
How can you get output voltage, if no input???
Please, post accurate information.
 

Holes Flow

New member
@2informaticos,

I'm very sorry, but that/those were what I read, when I read it. I am only reporting voltages I had read. I understand why this is frustrating for you. I apologize on behalf of myself & the LB! :)

And now, there is no voltage in or out of U8020.
VIN, EN and VOUT are all 0V now.

[May be significant: When the voltages were there, the board was drawing 19mA, not is the first time I have seen it change, and it is now at 14mA.]

I'm now watching the chip (U8020) to see if it is going up & down, but it has been plugged in this whole time (not repowered), and the ammeter is rock steady (at 14mA now instead of 19mA).

Also going upstream of VIN ( via PP3V3_SUS_P3V3SUSFET) to see where it stopped.

Sorry again...
 

2informaticos

Administrator
Staff member
STOP using lab PSU at this moment.
Find original 60/85W Magsafe 2 charger.
Why do you bother with current consumption, if don't get correct expected voltages?

"And now, there is no voltage in or out of U8020."
So you've actually lost 3V3_S5.
Follow power aliases on page 68, to understand power rails distribution.

What is now exact PPBUS_G3H voltage?
Check SMC_PM_G2_EN and PM_BATLOW_L.
 

Holes Flow

New member
STOP using lab PSU at this moment.

The PSU is connected to an 85W MagSafe. There are only 2 wires to the power supply from the MagSafe, no?
This is a LR technique, but the bench supply was at 16.5V.

Begrudgingly, I did as you said, on an 85W 20V PS. And I'll fess up... Fan Spin! Also, the laptop now works.

Thanks 2informaticos!
 
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