"Dead" iMac Intel EMC2389: Bad PSU or Logicboard?

[berniedd]

I was called on to diagnose this dead iMac (21.5 inch, EMC 2389). Owner said she was typing something in Excel, and the whole thing just died. She had the hard drive removed so she could get her data off it. She brings it to me and I remove the LCD.

I free up the power supply and all components look OK. I plug it in and LED #1 lights up. I press the switch and there is no response, and LED #1 goes dead. Other LEDS remain dead. So, what do you guys think? PSU or logicboard? The PSU has part # 614-0445. Other side of the board says it's an ADP-200DFB. The DC out connector has 14 pins, but I have no idea which pins should read what voltages. Pls guide me on what voltages to expect from which pins.

[berniedd]

Re: "Dead" iMac Intel EMC2389: Bad PSU or Logicboard?

Here's an update: I measured the voltages at the PSU output to the logicboard. With the iMac on standby (just plugged in to AC), pin 4 has 12.12 V (with respect to ground) and pin 6 has 4.0 v. After I press the power button (and diagnostic LED #1 goes dead), pin 4 still has 12.12 V and pin 6 now has 3.6 V. All other pins (12 in number) read 0 or near 0 V whether at standby or after I've pressed the power button. Sounds like PSU problem?

[budm]

Re: "Dead" iMac Intel EMC2389: Bad PSU or Logicboard?

There is label next to the Black connector to tell you what Voltages this power supply has, it is partially covered by the white glue so I cannot see what they are.

[berniedd]

Re: "Dead" iMac Intel EMC2389: Bad PSU or Logicboard?

budm, I have picked off the white glue, and I see 4 labels (12 or 12.1 volts+current rating) but none show which pins they should read from. So I guess the PSU is bad? Bummer.

[stj]

Re: "Dead" iMac Intel EMC2389: Bad PSU or Logicboard?

isnt that a good thing?
better than the main logic being bad.

[FloristePoele]

Its the Logic board. And the bad behaviour gets worse in cold conditions. Try in a warm summer/ environment: Hold down the start button, then plug in the mains cable, while holding down the start button a little longer - then let go of the start button... Wait .. sometimes it will start bij itself - or push the button once again. Nothing? Unplug the mains cable. wait a minute. (Try again on a warmer day!)

I'm still trying to get to the right solution...

[stj]

sounds like caps, they work better when warm.
try a hair dryer to locate the area that has the problem