iMac 820-2507-A (A1312) schematics and board layout

[okw]

I need schematics and board layout for Apple 820-2507-A. It's for an iMac late 2009 3.06GHz Intel Core 2 Duo (E7600).

Someone attempted repair on this and ripped the display port connector off without desoldering (probably accidentally while removing the display). Also, it has a burned inductor (L5720) (probably why repair was attempted in the first place). Due to poor storage, a transistor (Q5605) got whacked loose. It's an old iMac and slow compared to todays standards, but still performs good for designing PCB with its solid 27" screen. I really hope to get this baby up and running again.

Any help is appreciated. Thanks

[okw]

Re: iMac 820-2507-A (A1312) schematics and board layout

I got a hold of the schematics, but still missing the board. See attachment.

I replaced the Q5605, which is a 2N7002 (60V 210mA N-MOSFET) with a BSS138PW (60V 320mA N-MOSFET).

Display port connector is still missing so I'm running the iMac from an external monitor.

I tried powering her up, and there is some life in her. No chime. LED 1 is always on (power supply OK). LED 2 comes on when pressing the power button, right fan (optical drive fan) and hard drive spins up. After 3-4 seconds, LED 2 suddenly switches off along with hard drive and fans. Then they all come alive again, and stays alive. LEDs 3 and 4 is always dead.

The burnt L5720 is a 220ohm 1.4A ferrite bead. This connects the F2_GATESLOWDN signal (of NTHS5443T1H (power MOSFET)) to the MOTORCONTROL signal of the CPU fan. At the moment the CPU fan does not run (of course, since the L5720 is missing). I don't have this part, so as a brief test, I would like to try to short the L5720 pads and see if the computer proceeds to LED 3 + 4. Should I use a 220ohms resistor or just wire? It is rated 1.4V and fan voltage is 12V (16.8W) and I don't have such rated resistor.

I'm dreading the well-known faulty GPU (LED 3 indicating CPU-GPU communication). But... Could the CPU not running be the cause? Will the CPU check for a running fan before powering up?

Does anyone have experience the combination of LED1, then LED1+2, then LED1, and finally LED1+2 again? Does this sound like a faulty GPU?

[mcplslg123]

Re: iMac 820-2507-A (A1312) schematics and board layout

For testing sake, you can just jumper) with a very thin wire) the two points of L5720 though it should be replaced with exact parts if it works. That wont damage anything.

[okw]

Re: iMac 820-2507-A (A1312) schematics and board layout

Thanks. Yes, I thought so. Seems the L5720 ferrite bead is only for filtering fan noise, so shorting it for test shouldn't do any damage.

How about the intermittent shutdown of LED 2, then coming back on? What would that indicate? Could it be a short in the GPU? That the GPU is powered at this particular time, but power supply isn't able to supply due to the short, and resets or somthing? I've tried baking the GPU at 8 min 170'C, no success. I'll try again, 10 min at 200'C.

[piernov]

Re: iMac 820-2507-A (A1312) schematics and board layout

Try to boot the iMac without the GPU, and do a PRAM reset. It should chime if CPU is working (make sure speakers are plugged in). You will obviously get no display but the computer in itself should work. If it doesn't you've got another issue.

[okw]

Re: iMac 820-2507-A (A1312) schematics and board layout

I removed the GPU and the LCD inverter board, but I get no chime. Same intermittent LED 2 going dark, then illuminating again. Fans full speed.
Checked all the caps on power supply, extremely low ESR (good) and capacitance within spec.

Any ideas?

[okw]

Re: iMac 820-2507-A (A1312) schematics and board layout

Plugged in the display temp sensor. Fans now run at normal speed. So at least something works on the logic board

The logic board seems to power off the power supply when LED 2 intermittent shutdown happens. During standby PS_ON shall be 4V and PP12V_S0_PS shall be 0V. When powered PS_ON shall be 0V and PP12V_S0_PS shall be 12V. See pinout: http://hqlaptoprepair.co.uk/wp-conte...7/01/PSU-1.jpg

However, during the LED 2 intermittent shutdown PS_ON goes 4V, which leads to PP12V_S0_PS going 0V and system shuts down. Then PS_ON goes 0V and PP12V_S0_PS goes 12V again and LED 2 comes back.

Seems like the logic board is forcing the power supply to cut power? Or the power supply can't supply enough, so it resets itself (like there was a short somewhere)? Perhaps a re-balling issue.

At the moment I don't think there is a GPU issue, since it restarts PS by itself and no startup chime.

Are there anyone that can help me?

Sorry for spamming my own thread, but the troubleshooting is an iterative process