imac G5 iSight, psu 614-0394

[faithie999]

symptom:
when power button depressed, pilot light comes on for 1/2 sec, then fan at full speed for 1/2 sec, then powers down.

i dissassembled the imac. no obvious swelled or leaking caps on the logic board or power supply.

i read this thread: http://badcaps.net/forum/showthread....light=614-0394

and my PSU is the one pictured in post #4.

the fuse tests good.

when connected to AC, i get 11.56 volts across black and gray (both sets of black and gray) and negligible across black and brown (makes sense if brown is an input contact).

are there any diagnostic LED's on the logic board that i can refer to? googling reveals that there are on the non-isight 17" but i can't find reference to any on the isight version.

any other ideas?

thanks

ken

[Toasty]

Bad onboard battery. Post 25.

These are still to much money to even entertain the idea of buying one to tinker with.

[faithie999]

which thread? i used the search tool on the home page to search for "bad onboard battery" and didn't find a link to a thread with that many posts.

thanks

[Toasty]

The one you referred to...

[faithie999]

thanks. replaced the CMOS battery, reassembled the computer. now the symptom:

diagnostic LED's:
plug in AC--LED 1 lights, as expected
power on--LED 2 lights, as expected
pilot light at full brilliance, fan on low speed
no startup chime
screen is black
LED 3 never comes on

unplugged AC, then performed SMU reset procedure, then restarted trying to boot from install DVD--but superdrive never "swallowed" the disk.
same LED diagnostic--1 and 2 lit, 3 not lit; no startup chime, black screen

does this still sound like a capacitor problem, or should i head down a different road?
thanks in advance

PS--there is a white connector on the backside of the logic board (the non-component side), at the edge of the logic board closest to the superdrive. it is white, relatively wide, labeled SMU with the notation J2904. there is no cable plugged into it. i was able to find an Apple shop manual for this computer, and there are several pictures of the logic board, none of which appear to show anything plugged into this connector, and there is no mention of it in the manual.

i only raise the question because it is labeled "SMU" and the box doesn't boot.


ken

[Toasty]

Try SMU reset one of 2 ways-

(1) With cover on
Unplug unit from wall outlet.
Unplug any accessories from unit.
Wait a minute.
Press and hold power button while plugging in power cord to outlet.
Release power button after a few seconds.

(2) With cover off
Unplug unit from wall outlet.
Unplug any accessories from unit.
Wait a minute.
Press and hold SMU reset button on mainboard while plugging in power cord to outlet.
Release SMU button after a few seconds.

Unplug unit. Make sure LEDs are off. Re-seat the RAM and/or try different.

Double check all connections.

Toast

[b700029]

I should probably make a new thread, but I saw this post and decided to add on a bit, as my scenario seems to be almost the exact same and it might help the OP(though I wasn't sure if I should post in the power supply forum or somewhere else). I have an iMac G5 A1058 that I just fully re-capped with new Panasonic FM and Nichicon HZ (I could see multiple blown caps on the board). I am experienced in these procedures and there were no connections that I suspected to be faulty. Yet, when everything was assembled again, I got the exact same symptoms as the OP:

diagnostic LED's:
plug in AC--LED 1 lights, as expected
power on--LED 2 lights, as expected
pilot light at full brilliance, fan on low speed
no startup chime
screen is black
LED 3 never comes on

I have checked all connections and swapped around known-good RAM. I also performed both of your SMU reset procedures. There is one other symptom I have though that might give some clues. Sometimes (but not each time)when I plug the power cable in, there is a faint "cheet" sound coming from the power supply - it sounds like a sped-up grasshopper. The first diagnostic LED pulses to the sound as well.

I still have yet to take my multimeter to the power supply or open the power supply up, but...

[Toasty]

Time to pull the PSU apart.

The unit you have is the "standard" iMac G5. The OP's is the iSight version. Different beastie in many respects. Especially (it seems) with respect to video failures, which your model is notorious for.

iSight's have a built-in webcam at the top center of the casing above the screen.

Toast

[berniedd]

For iMacs, at least for PowerPC processors, here's the code for the diagnostic LEDs:

LED1 on= PSU sends power to the logic board while in standby mode.
LED2 on= PSU sends correct power to the logic board while in ON mode.
LED3 on= After turning the unit ON, Logic board is receiving video signal from the video chip. If the LED is OFF, suspect the GPU (video chip) as faulty.
LED4 is on = the computer is overheating.

I'm not sure if the same holds true for Intel iMacs.