820-00431-02 - 2 leds, no chime

Working on an iMac for a change. No real prior experience (ripped the power button cable already) but as it's pretty much a MacBook on the inside, I should be able to work on this quite easily.
  • 2 leds, no chime
  • All rails present
  • 5v rails are 5.1 - normal on these? or maybe just unloaded
Some signal measurements:
CPU_VCCST_PWRGD0.94V (a bit low maybe? PP1V05 = 1.05V)

I'll have a look around if I can find a BIOS to flash. Any other suggestions?


Staff member
Any history fault available?
Do you get correct RAM voltage?

BTW, above mentioned signals and voltage are good.
History: customer may have left it on in a closet when they left their shop. After the weekend they tried powering it on and it wouldn't do anything according to them.

All voltages look fine to me. Checked all rails on the 'power aliases' page in the schematic. This includes RAM voltages if I'm not mistaken.

Any point in trying a fresh BIOS? If so, do you know where to get a good bin?


Staff member
First remove CMOS battery and check if something change on its behavior.
Apart of automatic turn on, which is normal in such case.