iMac G4 15" [Nickjf20]

[nickjf20]

Good progress you made! It's good to hear, that you've fixed the LCD



I had a similar problem. It's essential, that all analog audio devices have the same, stable GND potential and that you don't have a GND loop. The solution is documented in this post:
http://www.tonymacx86.com/imac-mods/130197-mactester57s-imac-g5-17-a1058-model-11.html#post1043277

MacTester

Thanks MacTester, I'll get your fix implemented tomorrow.

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I've mostly finished the acrylic board that will hold all the new components. Most things are attached via small 6mm standoffs, which are in turn screwed into M7 nuts melted into the acrylic.

I found there wasn't enough room for everything on the bottom board alone, so I created a riser for the HDD and the SMC.

The 5V/3.3V downconverter is hot glued in to the riser.

Here's an overview. The HDD is held on by 2 screws at one end, and then a strip of velcro at the other. It should be OK (I hope!)

On the far left of the panel you can see where the acrylic cracked whilst drilling a mounting hole - forgot to drill a pilot hole first
Doesn't matter though, no-one will see it when everything is put together

 

[nickjf20]

Sadly I'm going to have to call this project a failure for now.

I've spent days trying to get everything to work, but to no avail.

The arduino will now just switch the audio output from 3.5mm to the internal amp. Nothing else.

The BRIX board is grounded and the audio ground lifted via a 10ohm resistor, but still outputs some annoying background noise into the amp and speakers.

The LED power state detection also does not work with the BRIX - the high side of the LED stays high during blinking, and even for some time whilst off.

The backlight also stays on when the BRIX is set to sleep the display. Why? I don't know.

As for the capacitive control for the backlight, I have the sensors working on a bench using the sample capacitive touch code, but cannot get them to work with Mactester's code.

There are also a fair few artifacts on the screen. Not too bad, but certainly noticeable.


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The iMac is going to be put back together as is, as I don't have the time to work on it anymore.

 

[nickjf20]

Everything is together now.

The background static over the pro speakers is still annoying, but far quieter than before the BRIX was grounded.

The screen artifacts are pretty much gone, but still there on certain shades of grey/black, not a problem as they're so rare!


I've just set the LED to be on all the time in the hope the iMac will be turned off at the wall more often than not as the original PSU currently runs warm even when BRIX is off, so I may change it for more efficient supply


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I found that if I set the powerState to 1 (i.e ON), everything worked as it should including the brightness dimming now the BRIX is grounded.
The fan PWM appeared to induce even more noise into the audio output, another reason why the fan was scrapped.
With everything connected to the iMac PSU, I tested the BRIX LED again with the multimeter:
I have no idea how the BRIX LED is being switched as the high side almost randomly switches from 2.95V to 4.95V. The low side switches between 0V and 2.1V in sync with the high side switching. Very bizarre.

For the 17" conversion, I'll go for the tried and tested NUC and reuse the Arduino board I've made here. So not all wasted!


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So, to conclude:

Working:
3 x Original USB 2.0 ports
USB 3.0 port replacing Firewire400
3.5mm Headphones with jack detect
Original Pro Speakers via inbuilt TA2024 amplifier

Gigabyte BRIX J1900
Wifi/BT antennas outside the faraday cage
Windows 10
500GB 'Apple' HDD from a MBP

Powered by original PSU

 

[nickjf20]

Screen artefacts have been fixed with a new HDMI cable.

Buying an actual NUC soon to use with the 17" and the (currently wasted) Arduino SMC