A1502 - 820-4924-A - light green and then orange without battery - Not turning on - CPU warm,3 beeps

[richiekotzen]

A1502 820-4924-A, e, no liquid, stop working suddenly. Yesterday, I've plugged magesafe, light green and then orange without battery,3 beeps, not turning on, CPU warm and at some point fan was spining but nothin on screen, .. no chemie.

[mon2]

What is the voltage to ground of PPBUS_G3H?

Also share the voltage to ground of each pin on D7005 which is linked to the critical PPVIN_G3H_P3V42G3H and PP3V42_G3H rails.

[piernov]

How could it make beeps if it's not turning on…?
https://support.apple.com/en-us/102210

[richiekotzen]

Hi
On the D7005 I have :
pin 1 - 16.13v
pin 2 - 12.54v
pin 3 - 15.86v

[richiekotzen]

I get 3 short beeps, a two second pause, and then 3 more beeps like before and it repeats over and over again

[mon2]

https://www.youtube.com/watch?v=KrVTzjVy3dQ

https://boards.rossmanngroup.com/threads/a1502-820-4924-a-3-beeps.60488/

[richiekotzen]

I have already tried reflowing all the RAMs as in the video, but the problem is still there, 3 beeps.
Unlike the video on my motherboard there are 4 memory banks I unsoldered 3 leaving 1 and the problem remains. I also unsoldered the last one and the problem remains I think because without ram. I reballed 1 chip but nothing same problem.

[richiekotzen]

Could it be a CPU problem? or corrupted Bios?

[mon2]

Remove all power. Disconnect the battery. Meter in lowest resistance scale (if manual type) or AUTO. Measure the resistance to ground of the CPU VCORE power rail. You can locate the multiple inductors (L7310/L7320) that will feed this heavy current power rail.

What is the resistance to ground in ohms at either of these inductors?

[reformatt]

I did have an iMac once where I had 3 beeps. Initially thought it was RAM, but turned out to be a shorted PP3V3_S0 power rail from the headphone jack board. So check all your switched S0 power rails for shorts before blaming RAM itself.

These boards won't boot without all RAM IC's fitted and working. If known good RAM's and switched power rails check out, then this would be a PCH issue I would think.

[richiekotzen]

Remove all power. Disconnect the battery. Meter in lowest resistance scale (if manual type) or AUTO. Measure the resistance to ground of the CPU VCORE power rail. You can locate the multiple inductors (L7310/L7320) that will feed this heavy current power rail.

What is the resistance to ground in ohms at either of these inductors?

The ground resistances are:
L7310 : 15.6 ohm
L7320 : 15.6 ohm
L7630 : 268.9 ohm - but every 6-7 seconds it drops to 140-142 ohm,to then go back to 268.9 ohm

[richiekotzen]

I did have an iMac once where I had 3 beeps. Initially thought it was RAM, but turned out to be a shorted PP3V3_S0 power rail from the headphone jack board. So check all your switched S0 power rails for shorts before blaming RAM itself.

These boards won't boot without all RAM IC's fitted and working. If known good RAM's and switched power rails check out, then this would be a PCH issue I would think.

Thanks for sharing your experience

[mon2]

Can you confirm that you are measuring the resistance to ground WITHOUT power to the board? It is not possible to measure the resistance if there is power (adapter or battery) to the logic board.

[richiekotzen]

Can you confirm that you are measuring the resistance to ground WITHOUT power to the board? It is not possible to measure the resistance if there is power (adapter or battery) to the logic board.

I confirm that the card was measured without any type of power supply and without batteries, nothing connected.