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Originalmente conocido como "El Nuevo iMac" el iMac G4 fue creado para reemplazar al iMac G3 como la computadora todo en uno de escritorio de Apple. El G4 es fácilmente reconocible por su pantalla giratoria montada arriba de la computadora hemisférica. Steve Jobs dijo que el iMac G4 es "diseño que durará hasta la próxima década."

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PSU voltage: 12 V stable - 5 V NOT stable

Hi ....

i hope that someone here can help me.

I habe a problem with my G4 that won't turn on.

I tried everything i found on the web including change of 3.6 LiIon Battery and all the reset stuff.

I ended up with disassembling the G4 and took a look at my PSU.

I measured some of the voltages ...

AC / DC Board gives me more than 400 V of a stable DC voltage

DC / DC Board gives me a stable 12 V voltage between one black (GND) cable and 4 of the yellow cables of the mainboard-plug.

But between the black cable and the blue cable i get voltages between 0.8 and 3 and just sometimes up to 5 V .... it isn't stable at all .

I suppose there should be a stable 5 V voltage between the black and the blue cable??

I tried changing some of the capacitorc on the DC/DC board (2*10uf and 1*1uf) because i heard that they often are responsible for PSU problems but it didn't change anything.

Should i try to change the other capacitors too ?

Or could there be any other reason for the unstable voltage ?

Hope someone of you can help me

Thanks in advance

Oliver

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Obi B, not sure where you got the 400V. May be you can post a couple of images and show us where you are measuring your voltages. Take a look at the attached image and see if you get those voltages.

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Hii oldturkey03,

thanks for response, sorry for late answering.

since 3 days iMac is up und running. Don't know what exactly solved my problem.

Changed 3 capacitors on DC/DC board i described in my first post.

Resoldered soldering joints from onboard connector on DC/DC board

Used contact spray on mainboard-cable-plug (blue cable)

checked if cables were well fixed in the plug.

Reasembled, now it's running!

@measuring voltage:

PSU in my case (G4 15 inch) consists of two parts.

1st part: The AC/DC board that converts ~230V AC to ~418 V DC and is connected to the DC / DC board with a two-core-cable.

2nd part: The DC / DC board that is supplied by the AC/DC board and has a 14pin connector that connects to the mainboard/DVD&HDD by cable.

My plug:

7 black (bk) on one side

4 yellow (y), 1 blue (b), 1 yellow, 1 red (r) on the other side

X = plug connector lock

y(2) bk (1)

y(3)

y(4)

X y(5)

b(6)

y

r

Again sorry for late answering, thanks

Oliver

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Obi B estará eternamente agradecido.
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