MacBook a1466 820-3209-a No Power No Fan vol fluctuating loop

[marce002]

Hello

Short Question is What can be wrong in the circuit that I have a current loop fluctuating from 9 to 5v, what i ve checked:

I have a 820-3209-a (macbook a1466 from 2012) Connect charger from my power bench and green led appear and then orange. The F7040 in the picture attached shows 9.06Volt for 3 seconds then decreases slighttly to 5vol in a loop, then 9,06V again and so on. no fan. consumptions goes from 18mah and then 6mah in that loop...
I have checked U7000 : AC OK, DC IN , AC IN, VDD, VDP are fine i think.....

capacitors arround are not shorted....

I have disconected one side of the L7030 coil to see if the problem is in the CHARGE side of the system or in the power supply side, and the problem is still with the coil disconnected from one side, so problem is in the power supply side, any hint willl be much apreciated..

[mon2]

Re: MacBook a1466 820-3209-a No Power No Fan vol fluctuating loop

Check your current sense resistors. If any of these parts are missing or open, the regulator will think too much current is being drawn and will shutdown to protect.

[marce002]

Re: MacBook a1466 820-3209-a No Power No Fan vol fluctuating loop

thanks mon2 , I will test it, I also wanted to say that the 3.3v and 5v power supply that uses a TPS51980 (UT201) has no output to the coils!! but it is enabled in both EN1 and EN2 and has REG2 and REG5 ok, also VIN is ok , and no PGOOD1 nor PGOOD2 (they are are 0v.)... can this mean the IC is faulty and make the IC in my previous post drop the current in a loop?

PD how can disable this TPS51980 to check if the main 9vol remains stable?

[mon2]

Re: MacBook a1466 820-3209-a No Power No Fan vol fluctuating loop

hi.

1) this is U7201 (TPS51980)?

2) Vin value on pin 23 ?

3) Good if you see VREG5 (pin 29) and VREG3 (pin 22) operational. Post their values for clarity. These rails should always be on as noted in the schematic. These are LDO (low drop out) regulators and are linear so no switching mosfets nor coils needed. Respectively, they "burn" the input voltage down to the lower voltage so they are only for low current loads as to not cause too much heat rise from this voltage conversion.

4) Post the voltage readings for EN1 (R7251) and EN2 (R7252).

5) With power off and the battery removed, using your meter in resistance mode, what are the coil readings @ L7220? L7260?

If these readings are low then there could be a shorted cap on the respective rail. Or could be a local bad mosfet that is not switching.

These regulators are quite common in Asia and should be easy to source. Good to grab a few for testing.

Yes, if this regulator is not operational then certainly other legs of the logic board will fail to operate correctly.

[marce002]

Re: MacBook a1466 820-3209-a No Power No Fan vol fluctuating loop

Mon2 thks!!!!!!!!!!!!!!!!!!!

1) yes

2) pin 23 ? it is: 9.1v and other relevant:

12=3.4v
4=4.95v
21=3.41v
5=0v
20=0v
23=9.1v
22=3.3v
29=5v







3) Good if you see VREG5 (pin 29) and VREG3 (pin 22) operational. Post their values for clarity.

posted above


4) Post the voltage readings for EN1 (R7251) and EN2 (R7252).

pin 4 and 21 above

5) With power off and the battery removed, using your meter in resistance mode, what are the coil readings @ L7220? L7260?

ok they are:

L7220=2.61kohm
L7260=2.22kohm
and
L7030=0.574kohm

[marce002]

Re: MacBook a1466 820-3209-a No Power No Fan vol fluctuating loop

Mon2 Remember that with the coil open or lets say the fuse f7040 removed i still have that unstable loop volt from 9v to 5v in PPBUS_G3H...
problem before any 5v or 33v generation at TPS51980...
so should look 4 issues "before the FUSE" ,,, what to look at?

thanks very much

[mon2]

Re: MacBook a1466 820-3209-a No Power No Fan vol fluctuating loop

Hi. I think we are working on exactly the same logic board at the office today. Bought from eBay and the seller said no idea on what is wrong. The logic board is missing many parts... thieves. We will rebuild it.

Check your current sense resistors on the bottom right of the same regulator. Confirm their values and they must reach the regulator.

If this area is broken then regulator will believe too much current is being drawn and will enter shutdown or hiccup mode like you are observing.

[mon2]

Re: MacBook a1466 820-3209-a No Power No Fan vol fluctuating loop

Hi. I think we are working on exactly the same logic board at the office today. Bought from eBay and the seller said no idea on what is wrong. The logic board is missing many parts... thieves. We will rebuild it.

Check your current sense resistors on the bottom right of the same regulator. Confirm their values and they must reach the regulator.

If this area is broken then regulator will believe too much current is being drawn and will enter shutdown or hiccup mode like you are observing.

Check r7050, r7051, r7052.

[marce002]

Re: MacBook a1466 820-3209-a No Power No Fan vol fluctuating loop

Mon2

from the side of charger the sense resistors are ok they are 10ohm each one: r7021 and r7022. and R7020 is 0,5ohm
In the battery side although I have:

r7050=0.06ohm
r7051= 10.4ohm *a bit off
r7052=0.8ohm

here is a picture of the wrong resistor, coud it be the culprit? can i make a bridge with pliers to do a fast check removing the existing one? pliers are 1,5ohm

Thanks a lot

[marce002]

Re: MacBook a1466 820-3209-a No Power No Fan vol fluctuating loop

I ve replaced that ugly resistor with a 2.8ohm and verified its path to the chip on each leg and is ok. but same thing, the fan does not spin.... so sad... maybe the chip is bad but i dont think so because has most of volt values ok (its cheap anyway).... what else to look at..

does not work also on battery only... nor power supply at 14.6v Magsafe 2 cable... only green led and amber after 3 seconds.



BATTERY ONLY

I have 7.55V steady on fuse f7040 .. not any other coil with vol. not spining. charger disconnected.

BATTERY AND CHARGER connected

I have 9.08 V o and 17mah steady on fuse

[mon2]

Re: MacBook a1466 820-3209-a No Power No Fan vol fluctuating loop

1) what is the voltage @ J6901 - pins 1 & 2?

2) voltage @ D6905, pin 3?

3) voltage @ L6995, pin 2?

4) Q7080, pin 1 ?

5) D7005, pin 3?

6) remove the battery and confirm if the voltage (PPBUS_G3H) still is oscillating.

7) If you remove L7030 - the switching regulator will no longer switch. Instead, remove F7040. Then measure the voltage @ L7030 pin 2. Do you see a higher and steady voltage on this rail? Value?

[marce002]

Re: MacBook a1466 820-3209-a No Power No Fan vol fluctuating loop

1) what is the voltage @ J6901 - pins 1 & 2?

J6900??? :1= cant measure because is the cable attached to the connector right?goes to a 8 pin component called q7080 =VFRAN .most of the 8 pines are steady 14,5V or power supply volt. one is 0V and the other pin is 13.93-13.81 loop.


2) voltage @ D6905, pin 3? varies little from 14.05v to 14.06v

3) voltage @ L6995, pin 2? 3.41v

4) Q7080, pin 1 ? (see point 1 above)

5) D7005, pin 3? 14,13v

6) remove the battery and confirm if the voltage (PPBUS_G3H) still is oscillating.

I ALWAYS HAVE THE BATTERY REMOVED in the tests, with only battery is steady, i do not know if the battery is good by remains stable at 7.55v


7) If you remove L7030 - the switching regulator will no longer switch. Instead, remove F7040. Then measure the voltage @ L7030 pin 2. Do you see a higher and steady voltage on this rail? Value?


FUSE REMOVED not STEADY, loop from 9.06 to 2.3v note 6seconds is 9.06 and 6 seconds down to 2.3v ...all this in a infinite loop like I said in the 1st post of this thread.

Bad luck still can I inject some volt to test somewhere? is your board the exactly the same? as i do not have J6901 DO YOU HAVE U7090? i do not see any 5v (5.5v "G3Hot" Supply) generation and i do not have any u7090 at all!!

[marce002]

Re: MacBook a1466 820-3209-a No Power No Fan vol fluctuating loop

update: same situacion but now have stable and steady 8.4V PPBUS_G3H no more loops and 17mah total consumption...

still no spin , I do have green led , then amber on my magsafe2 cable attached to my power supply. (what I think I did to solve that is resoldered the u7000)...

but still (UT201) has no output to the coils ...

[marce002]

Re: MacBook a1466 820-3209-a No Power No Fan vol fluctuating loop

Hello

LAST UPDATE!!

In order to do something with this mother , since it belongs to me, no worries
I have injected 3.3v and 5V with external sources to the corresponding places and I have made 'powergood' them. Now I have fan spining and all coils have its values ok (except for L9701 and L7550 but think is normal compared with another exact board) BUT no video NO chime .... I have USB activity and BIOS too.... when connecting display NO BACLIGHT/IMAGE at all... but when I attach a pendrive it acts like if it would be reading data.... led blinks normal...
QUESTION IS: THIS MEANS CPU IS OK? (vcore are fine on coil)... fuse F9700 backlight is ok, and ALL_SYS_PWRGD is good 3.3v too. 400 to 600 mah and fan accelerating


thanks for any idea!!!

[marce002]

Re: MacBook a1466 820-3209-a No Power No Fan vol fluctuating loop

Las update

Just to keep this alive, and to anyone reading, I hear a chime! so not dead CPU/PCH, but no image ....I suspect of the U9701 because no 20v are generated at L9701 even if the enable signal PPBUS_SW_LCDBKLT_PWR is present...

[mon2]

Re: MacBook a1466 820-3209-a No Power No Fan vol fluctuating loop

If you are still working on this case...

Yes, review page 65 of the schematic.

1) check F9700 for the backlight boost regulator Vin fuse.

2) PPBUS_SW_LCDBKLT_PWR voltage value ?

3) LCD_BKLT_EN voltage value ?

4) BKLT_PLT_RST_L voltage value ?

Changing the LP8550 is a common repair - available from Arrow or TI.com webstores.