iMac G4 17" Mod - The RochaMOD

[Juandelarocha]

Hello!

After a couple of weeks fighting to survive an old friend's iMac G4 15", I discovered this forum and the the mods you guys have been doing years ago. So I started searching for 17" units (locating a single unit of the 20" has been an impossible task, not sure if it was sold here in Spain). After some research I purchased three second hand units:

1. First unit I got (17" 1Ghz, 100€) was perfect. It worked so well that I kept it as it is and gave it to my friend to substitute his 15" - it gives smooth Photoshop performance under 2 GB ram and airport extreme WiFi card permits e-mail reading.
2. Second unit I purchased was even better: whole set including speakers for 100€. However, this unit doesn't boot up (original PSU not working and loosy neck)
3. Third unit was only 20€ and only included the upper part, that is, screen and dome. No motherboard, no CD, not even the bottom part with I/O sockets.

The point is to use parts of each of them so as to get a complete pristine unit. The mod includes a refurbished NUC5i3RYK purchased for 140€, 8GB of RAM (60€) and 120B of SSD M.2 (70€). So pretty much a low-cost high-performance mod.

First thing was trying the inverter of 3rd unit.

After having all set, when turning the PSU on all I could see was 1 sec flashlight at the screen. I checked the wiring and everything seemed to be OK. Then I remember about reading the same issue at the forum and all comments pointed a matter of GND connection. So I plugged one crocodile from the faraday cage to the crocodile giving GND to the black wire of inverter cable: that was it. It seems that even though testing the inverter (that apparently does not intervine with the cage) this must be given an stable GND. For more detail of connections, check out this video:

Next step: wiring the LMVDS cable and getting two 5.5/2.5 female connectors out of the single cable of NUC PSU (one for the PicoPSU and the other one for the NUC). Keep you posted!

 

[Juandelarocha]

Updates on the Rochamod.

I continued working on the wiring of the LCD. Some pictures with the advance:

Detail of the Vedid wire and red inverter wire with the 1Kohm resistor.

I have to say that I was afaid about getting extra wires and its "tinny" connectors. What I don't understand is why nobody said that, when preparing the LCD wires that would be connected to 3.3V at the PICO, some connectors could be obtained and so no extra wires from other neck were needed.

Advice: I would suggest to follow instructions from Mactester or Erstherhernd 'cause DremelJunkie instructions seem to be outdated (5V in Green Inverter wire for instance).

Everything set up and working!

Then I had some questions about how to solve the power supply wiring... My NUC came with a "wall-mount" PSU so here's what I did:

I took out the zone connector (EU-USA-UK) and soldered directly the cable coming from the filter (actually I employed the pigtail coming from the original Apple PSU).

Then I had to obtain from the cable coming out of the NUC PSU, two 5.5mm/1.5mm connectors to power both the NUC and the Pico PSU.

So now tasks pending are:

* Wiring everything inside the dom.
* Cut the original motherboard, and solder audio cables, ON/OFF button, Ethernet connector and USB connectors.

However, I'm not happy enough because I kind of see the screen dim. I mean, both using an external laptop or the original NUC, I've got an image as if it would be very low lightned. Initially I thought it could be that the ineveter was not working and so no backlight was flashing beneath the LCD image, but clearly the problem must be related to the connections.

The inverter connections that I actually have are:

Black wire -> GND at Pico PSU.
Blue wire -> 12V at Pico PSU.
Red wire -> DVI pin 14.
Green wire -> 3.3V through 1kohm resistor.

Orange wire -> floating.
Purple wire -> floating.

Should I connect orange wire to 3.3V? Should I try to install the potentiometer configuration? (i'm not up to proceed with PICAXE solution...)

Thanks!

 

[Juandelarocha]

In this video you can check the brightness of my screen and compare it with the one of the laptop connected.

** I'm trying to post a youtube video showing the dim image but it seems I'm not permitted. Please, is there any admin that could allow me to post it? Thanks!

 

[Juandelarocha]

And here´s another video that shows clearly the difference between brightness of Laptop computer screen and iMac screen.

UPDATE: Problem solved. By mistake I employed 10 Kohm resistors (both in red inverter wire pin14 to pin 16 and green inverter wire). That was the reason why hooking the green inverter to 5V instead of 3.3V was giving me better brightness!

I managed to change the resistors and now everything works fine in 3.3V without pluging both purple and orange wires from the inverter (they're just floating now).

 

[aldokun29]

Good work!

 

[pcmofo]

And here´s another video that shows clearly the difference between brightness of Laptop computer screen and iMac screen.

UPDATE: Problem solved. By mistake I employed 10 Kohm resistors (both in red inverter wire pin14 to pin 16 and green inverter wire). That was the reason why hooking the green inverter to 5V instead of 3.3V was giving me better brightness!

I managed to change the resistors and now everything works fine in 3.3V without pluging both purple and orange wires from the inverter (they're just floating now).

If you vary the voltage to the green wire between 0.6 and 3.3v it will change the brightness, hence why your 10x resistance reduced the brightness. A 1k resistor is still needed to reduce the current I believe.

Thank's for the great pictures of your mod. I am having trouble with my LCD. If you happen to see what I'm doing wrong it would be greatly appreciated.