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Board A1342 2010, 820-2877, fan spins, no chime

V

VinceLx

Member
Hello all,

- Green light on charger OK, I=0.65A with U=18.5V
- Fan spins OK
- No chime, no backlight
- Mouse in USB: pulse of red light when starting, then off

All rails are ok

Measuring - I put () for the theoretical values on the schematic:

S0 rails:
PPVCORE_S0_CPU (1.25V):0.99
PP1V05_S0 (1.05V):1.06
PPVCORE_S0_MCP (1.05V): 0.95
PPDDRVTT_S0 (0.75V): 0.76
PPVTT_S3_DDR_BUF (0.75V): 0.76
PP1V5_S0 (1.5V): 1.51
PP1V8_S0 (1.8V): 1.82
PP1V05_S0_MCP_PLL_UF (1.05V): 1.05
PP5V_S0 (5V): 5V (FAN)
PP3V3_S0 (3.3V): 3.31
PP3V3_ENET (3.3V): 3.31
PP0V9_ENET (0.9V): 0.91

S3 rails:
PP1V5R1V35_S3 (1.5V): 1.52
PP3V3_S3 (3.3V): 3.32
PP5V_S3 (5V): 5

S5 rails:
PP0V9_S5 (1.05V): 0.91
PP3V3_S5 (3.3V): 3.32

G3H rails:
PP3V42_G3H (3.42V): 3.39
PPBUS_G3H (12.6V): 12.6
PPBUS_S5_IMVP_VTT_ISNS (12.6V): 12.6

I played around backlight:
PBUS_S0_LCDBKLT_EN_L: 12
BKLT_PLT_RST_L: 0

So my rails are ok, but the CPU does not start it seems? Any idea why?
 
2informaticos

2informaticos

Administrator
Staff member
Forget "theoretical values on the schematic" and do not make wrong assumptions in the future.
"PP0V9_S5 (1.05V): 0.91"
Why would you expect 1.05V on a power rail named "0V9"???
VCORE is also dinamic voltage...

Is an old machine, MCP can be dead by now.
Post resistance to ground at 3V42_G3H; use ohm scale.
 
V

VinceLx

Member
Hello,
On the list of S5 rails, the schematic says 1.05V for PP0V9_S5. So we should trust the value inside the name, not the one in the schematic?

Resistance to ground at 3V42_G3H: starts at 20Mohm, decreases, then stabilizes after several seconds at 223kohm
 
2informaticos

2informaticos

Administrator
Staff member
Apple (and not only) has not interest to make repair job easy.
I wonder why did you take as good that notation and not the name.
Why do assume one thing and no other?
I mean, do not assume without reasoning.
The measured value at least matched one noted value; why did expect the other value?
When you have doubt ask, but do not assume!
Is not a critic believe me.

Try known good BIOS file...
 
V

VinceLx

Member
Unfortunately for this one I have no BIOS chip to swap and try, so it may finish as a donor board... Or I buy one faulty on Aliexpress for 15?? Any experience about this provider for spare parts?
 
V

VinceLx

Member
I found a good working board with same reference and swapped the BIOS chip; still the same issue (and the BIOS works fine on the other board).

I also noted that the current on the good board, with only USB mouse connected and red light, fan full speed, is around 0.9A. On this bad board, same configuration, the current is only 0.67A (no red light on mouse). So, something is not active?
 
2informaticos

2informaticos

Administrator
Staff member
Heat MCP for test; no more than 180-200 degrees fr 15-20s.
You don't need to melt the balls, just heat test.
 
V

VinceLx

Member
I forgot to mention the behavior of the fan. After switched on it runs normally until full speed 10s, then stops 1s, then goes again until full speed and does not stop anymore.
Same thing after heating MCP, no light on mouse.
Should I put back the heatsink after heating the MCP? If I don't put the heatsink the current is higher, but I believe because of the heat? If I put back the heatsink the current is as usual, 0.67A
 
2informaticos

2informaticos

Administrator
Staff member
Do you get LPC_RESET_L and PCIE_RESET_L?
Also check MCP_PS_PWRGD and PM_SYSRST_DEBOUNCE_L.

Can you detect any activity at MOSI/MISO/CLK pins of U6100?
Use an o-scope...
 
V

VinceLx

Member
LPC_RESET_L : 3.3V
PCIE_RESET_L : 0V (without LCD connected. I have 3.33V on the good board in same conditions)
MCP_PS_PWRGD : 3.32V
PM_SYSRST_DEBOUNCE_L: 3.31V

Activity at MOSI/MISO/CLK pins: nothing; but I have nothing on the good board either. I checked on a A1278 board, and there I could see the CLK and some signals on MOSI/MISO pins (double-checked with V-meter: nothing on the A1342 boards, while I see activity between 0 and 3.3V on A1278 board)

What can set PCIE_RESET_L to 0V?
Is the functioning of U6100 different on a A1342 board and A1278? Why I don't see activity?
 
Last edited:
2informaticos

2informaticos

Administrator
Staff member
Why do you expect to be an input issue?
Don't you think an internal issue is good enough?
That chip has more than 10 yo...
 
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