iMac SMPS - Page 2

pinkmouse · 26th November 2006, 11:05 PM

And a view from the top looking towards the traffo:

jleaman · 26th November 2006, 11:06 PM

pinkmouse,

You Got Mail.!

pinkmouse · 26th November 2006, 11:19 PM

Thanks Jason, but the problem is not with that board, I just need to get high frequency 24V ac into it, normally provided by the huge iMac PVB, (power and video board, but don't let the video bit distract you, it means CRT driver stuff).

Eva · 27th November 2006, 03:11 PM

Hi pinkmouse, can you provide a better quality version of the picture from post 9? The dirt and the fact that it's out of focus is preventing me to see most of the tracks. It may not be 24V HF as you think.

pinkmouse · 27th November 2006, 03:27 PM

Eva, dusted as requested!

I've ordered an ATX psu from ebay, it was ony a fiver so I do have a fallback plan, but I would still really like to get this working. It would be so much more compact.

Eva · 27th November 2006, 04:01 PM

Well, it seems that they use a linear regulator for the 12V output and magnetic amplifiers for the 5V and 3.3V outputs. The transformer is then fed with high frequency AC so you were right. The AC waveform may be either unipolar (switching in one direction for 50% of time and allowing the transformer to demagnetise for the other 50% of time) or bipolar (produced by a full bridge). The frequency also remains unknown, you would have to do some bench tests in order to know how long it takes to saturate and derive a suitable frequency.

Do you still have the circuit that provided the 24V AC? A quick look at the topology would already tell me if it's unipolar or bipolar.

pinkmouse · 27th November 2006, 06:31 PM

Thanks for all your assistance Eva.

Ok, here is the main power board. The connector where the 24V comes out is indicated by the yellow arrow. The stuff that isn't in the pic is the CRT stuff - flyback traffo etc.

pinkmouse · 27th November 2006, 06:33 PM

And the underside, connector again marked, as is the extent of the 240V circuitry.

Eva · 27th November 2006, 06:37 PM

Great, this one looks like a big off-line flyback. Can you take a couple of clear pictures of the bottom side of the board? The interesting portion goes from the big heatsink to the small heatsink (including it) and the edge of the square hole.

They may be slaving the other transformer to the flyback and attaching the primary of the other transformer directly to the secondary of the flyback.

Oh, and try to read the model of the big swithcing IC in the big heatsink, it will probably tell us the switching frequency.

pinkmouse · 27th November 2006, 07:02 PM

Good job I put the batteries on charge!

Ok, here is the bottom immediately under the traffo, heatsink is towards the top:

26th November 2006, 11:19 PM	#13
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Thanks Jason, but the problem is not with that board, I just need to get high frequency 24V ac into it, normally provided by the huge iMac PVB, (power and video board, but don't let the video bit distract you, it means CRT driver stuff). __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

27th November 2006, 03:11 PM	#14
Eva diyAudio Member Join Date: Oct 2003 Location: Near the sea	Hi pinkmouse, can you provide a better quality version of the picture from post 9? The dirt and the fact that it's out of focus is preventing me to see most of the tracks. It may not be 24V HF as you think. __________________ I use to feel like the small child in The Emperor's New Clothes tale

27th November 2006, 04:01 PM	#16
Eva diyAudio Member Join Date: Oct 2003 Location: Near the sea	Well, it seems that they use a linear regulator for the 12V output and magnetic amplifiers for the 5V and 3.3V outputs. The transformer is then fed with high frequency AC so you were right. The AC waveform may be either unipolar (switching in one direction for 50% of time and allowing the transformer to demagnetise for the other 50% of time) or bipolar (produced by a full bridge). The frequency also remains unknown, you would have to do some bench tests in order to know how long it takes to saturate and derive a suitable frequency. Do you still have the circuit that provided the 24V AC? A quick look at the topology would already tell me if it's unipolar or bipolar. __________________ I use to feel like the small child in The Emperor's New Clothes tale

27th November 2006, 06:37 PM	#19
Eva diyAudio Member Join Date: Oct 2003 Location: Near the sea	Great, this one looks like a big off-line flyback. Can you take a couple of clear pictures of the bottom side of the board? The interesting portion goes from the big heatsink to the small heatsink (including it) and the edge of the square hole. They may be slaving the other transformer to the flyback and attaching the primary of the other transformer directly to the secondary of the flyback. Oh, and try to read the model of the big swithcing IC in the big heatsink, it will probably tell us the switching frequency. __________________ I use to feel like the small child in The Emperor's New Clothes tale

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26th November 2006, 11:06 PM	#12
jleaman diyAudio Member Join Date: Apr 2002 Location: Nanaimo	pinkmouse, You Got Mail.!

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