Hi! I have this imac with diagnostic LED 1 on and LED 2 blinking. I tested all the S5 rails present and working well. I couldn't find any evident short lines. I tested the board with and without ram with no different results. When led 2 flashes, all rails (S4, S0) are high at that moment and there is a peak of 0.8 A on the power source. I need advice.
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Imac 27 A1419 820-3299a with diag #2 Led flashing.
- Thread starter Scultetus
- Start date
First of all, welcome to the forum!
Isn't 3299 board model?
Q7950/70 fail a lot on this board.
Looks like Q7970 is good in your case; stable S5 LED.
Do you get 22V at R7953?
Check for pulse at least.
Isn't 3299 board model?
Q7950/70 fail a lot on this board.
Looks like Q7970 is good in your case; stable S5 LED.
Do you get 22V at R7953?
Check for pulse at least.
PP12V_S0_FET pulses at same time?
If not, change Q7950.
Be sure first, no short to ground.
If not, change Q7950.
Be sure first, no short to ground.
Change Q7950, just in case...
I am waiting for a donor card and I will change Q7950 as soon as it arrives.
In the meantime, if possible, I would like to understand the board's powerup process.
I watched several videos of Louis on the macbooks, but found nothing on the iMacs.
I already fixed a macbook with a problem in one of the resistors of the current sensing circuit and I was wondering if this loop on and off on led # 2 could indicate something similar.
When the board receives power, are all lines energized for load testing?
Is it safe to power this card without the processor?
How can I test if any processor power lines could be shorted?
I would really love to understand a little more about what is going on with this iMac startup.
Thank you for your patience.
Power on sequence is controlled between SMC and PCH, like in a MacBook.
Signal names are the same.
Just need to pay atention at enable signals for secondary power voltage.
Finally all them derive from a PM_SLP_Sx_L signal, or from a power good of previous required voltage.
Forum goal is to assist on repair process.
For personal training, contact Rossmann staff.
Signal names are the same.
Just need to pay atention at enable signals for secondary power voltage.
Finally all them derive from a PM_SLP_Sx_L signal, or from a power good of previous required voltage.
Forum goal is to assist on repair process.
For personal training, contact Rossmann staff.
I tested all the rails and some are really low-resistance.
I would be grateful if someone could indicate to me if these resistances are within what is considered normal:
PP1V05_S0_CPU - 5 ohms
PP1V05_S0 - 28 ohms
PPVCORE_S0_CPU - 0.4 ohms (i7 CPU)
PPVAXG_S0 - 0.5 ohms
PPVCCSA_S0 - 3.2 ohms
PPVCORE_S0_GPU - 12 ohms (680mx GPU)
PPFBVDDO_S0_GPU - 60 ohms
PP1V05_S0_PCH - 30 ohms
Thanks.
I would be grateful if someone could indicate to me if these resistances are within what is considered normal:
PP1V05_S0_CPU - 5 ohms
PP1V05_S0 - 28 ohms
PPVCORE_S0_CPU - 0.4 ohms (i7 CPU)
PPVAXG_S0 - 0.5 ohms
PPVCCSA_S0 - 3.2 ohms
PPVCORE_S0_GPU - 12 ohms (680mx GPU)
PPFBVDDO_S0_GPU - 60 ohms
PP1V05_S0_PCH - 30 ohms
Thanks.
1V05 CPU can be good.
But VCORE and VAXG should be 1-2 ohm for i7 Ivy Bridge CPU.
But VCORE and VAXG should be 1-2 ohm for i7 Ivy Bridge CPU.
Did you change Q7950?
Not yet.
Please don't get me wrong, I consider your advice to be of great value and I will replace the mosfet as suggested.
I live in Brazil and even parts like these have to be imported from other countries or removed from donor boards. I did both, bought a donor board and ordered the transistor and unfortunately I still have to wait a long time to receive them.
Thanks for the tip! In fact, I ordered a PC motherboard to test this processor and I will probably have it on hand tomorrow or the day after tomorrow. I will also have another CPU in the next few days.
I tested the logic board with the resistor R6903 in place (as suggested and shown in the schematics) and led # 2 stopped looping on and off.
PP12v_S0 is present and stable.
PPVCORE_S0_CPU gradually goes up to 1.5V.
PPVAXG_S0 gradually goes up to 0.6V.
The board is consuming a constant 0.9 amps at the 12V input.
Some questions:
1) Is it normal, in this situation, for all voltages to appear without the SMC_ONOFF_L signal being set low? Why does the board go to the S0 state? Perhaps a wake event set by the PCH?
2) Although I am still not sure if the CPU went bad, what should I check before placing another CPU on this board? I wouldn't like to kill a new CPU for some silly oversight.
Thanks!
Last edited:
Gurmon
Member
Your measurments indicate bad cpu, considering without the cpu you are now getting voltage
Yes, I agree, but cpus generally doesn't go bad without a reason and that's why I'm concerned.
Am I forgetting to check something else?
Any reason to quote ENTIRE posts visible few centimeters above???
As you didn't get overvoltage on CPU power rails, should be safe to test with good CPU now.
As you didn't get overvoltage on CPU power rails, should be safe to test with good CPU now.
I have feedback.
I received the new processor and before testing it on the board under analysis, I tested it in a PC setup to make sure it was in good condition.
This test being good, I removed the resistor R6903 and installed the new CPU.
As a result, I again have LED # 2 flashing.
I also tested the original CPU on the PC setup and found it to be good too.
Definitely what is causing the problem is not the CPU.
I will probably have the Q7950 available next Monday.
@2informaticos, do you believe that this mosfet (Q7950) is not supporting the load when the CPU is installed?
Any other suggestions?
Thanks!
I received the new processor and before testing it on the board under analysis, I tested it in a PC setup to make sure it was in good condition.
This test being good, I removed the resistor R6903 and installed the new CPU.
As a result, I again have LED # 2 flashing.
I also tested the original CPU on the PC setup and found it to be good too.
Definitely what is causing the problem is not the CPU.
I will probably have the Q7950 available next Monday.
@2informaticos, do you believe that this mosfet (Q7950) is not supporting the load when the CPU is installed?
Any other suggestions?
Thanks!