Only LED 1+2 and no chime, fans + HD spins

I just bought an iMac late 2009 3.06GHz Intel Core 2 Duo (E7600) but it has some issues. It does not boot, and no startup chime. LED 1 is always on (so PS is good?). LED 2 comes on when pressing power, so does the hard drive (I can hear it spins) and fans run normally (once I forgot to put in the display temp sensor and fans went full speed). However a few seconds later, LED 2 goes dark and hard drive + fans stop. PP12V_S0_PS on power supply also drops from 12V to 0V (see measurements below). Then LED 2 comes on again, hard drive and fans starts and PP12V_S0_PS is back to 12V, and they stay powered until I manually power it down again. Can someone confirm this LED 2 on/off/on is normal or faulty behaviour? Seems strange to me. Also there is no backlight in the display. No signal to external monitor.

Anyway, lacking light in LED 3 I figured this is a GPU issue. However, I removed the GPU and still getting the LED 2 on/off/on behaviour. Still no startup chime. So I can't rule out logic board or CPU. Logic board is Apple 820-2507-A. Also removed all memory, inverter board and BT module to see if behaviour changed. No luck.

The previous owner attempted repair on this and accidentally ripped off the display port connector without desoldering while removing the display. It also has a burned ferrite bead (L5720, noise filtering between MOSFET and motor control signal to CPU fan). I temporarily shorted this to get CPU fan running (in case there is some logic not powering the CPU if fan is faulty). Due to poor storage after failed repair, a transistor (Q5605) got whacked loose. This is a 2N7002 (60V 210mA N-MOSFET) for switching the HD fan, and I replaced it with a BSS138PW (60V 320mA N-MOSFET). All fans run great now.

I measured the power supply according to this pinout: http://hqlaptoprepair.co.uk/wp-content/u...

STANDBY:

--Left--

INVERTER-: 0V

INVERTER+: 3.3mV

INVERTER+: 3.3mV

PP12V_S0_PS: 3.3mV

PP12V_S0_PS: 3.3mV

PP12V_S0_PS: 3.3mV

SMB_ACDC_SDA_RC: 0.66V and ramping up (2 min later, 0.78V) (same as SCL, I2C communication?)

GND: x

--RIGHT--

INVERTER-: 0V

GND: x

PS_ON: 4V

GND: x

PP12V_G3H_ACDC: 12.07V

GND: x

SMB_ACDC_SCL_RC: 0.66V and ramping up (2 min later, 0.78V) (same as SCL, I2C communication?)

GND: x

POWERED:

--Left--

INVERTER-: 12V between INVERTER-/+

INVERTER+: 12V between INVERTER-/+

INVERTER+: 12V between INVERTER-/+

PP12V_S0_PS: 12.07V

PP12V_S0_PS: 12.07V

PP12V_S0_PS: 12.07V

SMB_ACDC_SDA_RC: jumping between 3.253V and 3.372V

GND: x

--RIGHT--

INVERTER-: 12V between INVERTER-/+

GND: x

PS_ON: 0V

GND: x

PP12V_G3H_ACDC: 12.07V

GND: x

SMB_ACDC_SCL_RC: jumping between 3.253V and 3.372V

GND: x

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!