iMac G4 20" | For The Love of Mod

Hello, inspired by the many outstanding mods on this board I thought I'd join in with a tried-and-tested iMac G4 modification built on the shoulders of giants.

I began with a fully functional iMac G4 USB 2.0 20" Model, working pretty well actually. LCD and PSU are in great shape!

Hoping to use the native PSU to power the native 20" screen (LCD +Backlight) as well as a very low power consuming mobo (as per spong_jojo's mod), cpu (with integrated graphics). Furthermore I'll attempt to re-work the existing USB, NIC and Audio Lines including that genius hack by wingworm that allows Native Pro Speaker support. I'd also like a firewire 800 port!

As for a motherboard (I haven't built a Hackintosh before and haven't tinkered with motherboards etc for 10 years.. things have changed it seems) I have a DFI Lanparty P55 T36 sitting around - but I think the power requirements would be too much for the native PSU... powering a mini-ITX plus LCD and Backlight? Also, mini-ITX may be OTT for my bottom line: low power consumption.

In short:

• Original 20" LCD +Inverter
• Native PSU
• Low Power Motherboard
• Low Power CPU +integrated graphics
• Original I/O: x3 USB 2.0 | Firewire 800 | Ethernet NIC | Native Pro Speaker Support
• Native Mic

Anyway– thought it would be worth posting as I follow other's mods. If only to formalise my notes for future alterations. Nothing new here, hope you don't mind .

1. Starting with dremmeljunkie's TMDS > DVI

Last night I spent nearly 4 hours manipulating tiny TMDS pins from the native 20" LCD, soldering those teeny wires to resistors, separately preparing the native PSU. First de-tour from 'the manual' that is dremeljunkie's website, I purchased a different DVI part:

Molex Part Number: 74320-1003 offers the almost exact same design (though it has unnecessary analog pins) as the part dremeljunkie suggests. After reviewing the data sheet the only difference is the thickness of the pins, I took a gamble as the suggested part wasn't available to me. The thickness of the 'Plating min - Mating' pin on 74320-1003 is 0.762µm compared to dremeljunkies' 0.051µm.

Luckily the pins slip on with a little resistance, which I think is a good thing.

As intend to use the native (fully tested) PSU I followed another or dremeljunkie's guides and used Pin #14's 5V current to connect to the white wire of the PSU which enables the 24V required to power the backlight.



Hooked it all up, after double checking then double checking again after a particularly strong cup of tea flicked the switch...

---

Problem: though the screen turns on (with many green artefacts like a splatter of paint) when connected to a DVI source, my MacBook via the thunderbolt adapter, there is a high pitched screech emanating from the PSU.

I'm uncertain if this is due to soldering or pin connections on the back of the DVI 74320-1003 - however I immediately switched everything off and decided to sleep on it.

Those pesky green artifacts, ugh!

My 20" G4 build completed early 2014 caused me a ton of grief getting a clean video signal. Good luck with this, its worth it when you get it done.


Cheers!

Ersterhernd

Good afternoon Esterhernd- how funny to see your name on my post after weeks of reading yours! May I ask a quick question, regarding your comments:

... (discovered the LCD) requires 3.3V to the VEDID wire (as per the mfr spec), not 5V as is supplied from the DVI. It was a tedious task to repair, but may save long-term damage from over-volting pin 15 of the TMDS...

Click to expand...

Does this affect my 20" LCD also, should I roll by your rules or as per the great dremeljunkie's instruction?

How's your iMac going? All well I hope. Thanks for your comments. I'll persevere. Certainly agree with your comment that this is a most tricky step. Any thoughts on my whiney PSU?

Hi callumalden, I've run several 20" panels connected with the VEDID to 3.3 volts in various iMac builds. Less volts is better if it works ok, in my opinion. Perhaps give it a try to see if you get a signal.

The artifacting issue in my G4 was never resolved until I switched the system from an HD5000 NUC to an HD4000 model. Additionally, I never had success using the thunderbolt port converted with a mDP to DVI converter. That combo yielded green artifacts consistently across several panels. HDMI to DVI was the only conversion that was clean.

The whining in your PSU is odd. I've had issues with ground loops in the audio circuit that I solved by adding a little (56 Ohm) resistance to the ground wire. Perhaps try this on your video circuit.

My G4 has worked without issue since completion and is currently at 10.10.2 OSX.


Cheers!

Super, great to hear your thoughts on that ersterhernd.

More progress yesterday, re-soldered some of the connections and resistors. Double checked pins on the DVI female connector (74320-1003) and flicked the switch. DVI connected via an adapter (not official Apple part) to MBP. Still artifacting but I think I'll put that down to the adapter / MBP's graphics card for now. Need to find something else to test this out.

Artifacts are mostly a solid lime green, however some flashing.

Manipulating pins on the dvi has no effect. Confident connection is okay.

---

PSU / Power Problems: I find dremeljunkie's guide very confusing when it comes to hooking up the "Native iMac 20" PSU", not entirely sure I've got it right. Tried re-wiring this, found the high pitched 'eeeeeek' noise occurs (see video) even when no DVI (and therefore 5V current to enable 24V) is present.

Perhaps the PSU always made this noise? Maybe I couldn't hear it over the HDD etc. in the iMac when it was a happy little G4. Just to check (your thoughts welcome) here's how I'm connected to PSU at the moment.



12V Out (#9 Yellow) goes to Grey Cable (Purple-Yellow-Orange), the corresponding ground (#1 Black) is plugged into Grey Cable (Blue-Green-Gray & Pin 15 of the DVI via a cable, I used Green)

5V Switch In (#5 White) is connected to the DVI Pin 14 via a mess of connections to other places. Ground for Switch In (#13 Blue) connects to a spare ground (#2 Black).

24V Out (#16 Green) is connected to the Inverter Cables' (Red-Blue) and the Ground (#8 Black) to the Inverter's ground (Green/Black).

This works to the degree that a the screen comes on when DVI input is added but I'm worried about the high pitched sound. Tried a suggestion from ersterhernd of using a resistor on the Grey Cable ground (Blue-Green-Gray & Pin 15 of the DVI via a cable). I used a 6.9K Ohm as that's all I had spare.
- scratch that, now using the upconverter for this.

Today I received some additional parts including a 12V > 5V (3A) (15W DC) converter. Perhaps I'll re-rig the power with that as per dremeljunkie's blog post.

Great deal of success today. Hooked up my DFI mobo and installed OSX without a hitch. Also re-wired DVI and bingo. No artefacts. That was tricky. My first real electronics job tbh, 5hrs alone spent fiddling and using tiny bits of tape to ensure no crosstalk. All good there.



PSU Noise: still continues. Begins with when you flick the power switch (mobo off- using a separate PSU for that at the moment). As soon as the power is on, the high pitched noise emanates from the iMac G4's native PSU. I tried a resistor (6.8K Ohm) on the Grey Cable's ground (Gray-Green-Blue) as per above suggestion. Didn't help.

Note- if I disconnect or manipulate (carefully) the 12V Out (PSU: #9) the noise changes slightly.

These 4 Yellow (12V) and corresponding 4 Black (Grounds) are live as soon as the PSU is turned on at the wall. So the issue is probably with my PSU rather than the wiring.

... I'm currently using a 12V > 5V downconverter to enable the PSU.

Any ideas most welcome. Perhaps I'll try one of the other 12V outputs?

THEN– I wanted to test whether removing the DVI would switch the backlight off. silly thing to do, I should have just put the OS to 'Sleep') anyway, it works from the mobo.

However re-attaching the DVI... only the backlight switches I now get no picture from the mobo (gt610). Re-boot and still nothing.

Mobo fine on separate screen, same cable.

Weirdly; attaching my MBP via adapter allows the screen to work (with artefacts I'm now certain are caused by the adapter). Putting the MBP to sleep does not affect the backlight, it remains on.

Oh deary, where have a I gone wrong!?

A dvi-d to hdmi converter did the trick. I am up and running. Now on to the motherboard installation. I'm going to be bold and try and fit a mini-ITX and a full graphics card in there. Depending on how I go about cooling this it could work. Native PSU still buzzing.

Turning to wingworm's wonderful iMac G4 20" mod for inspiration.

So a note to anyone attempting the TDMS to DVI conversion in the future; I have learned that not all cables are made equal.

By having a selection of adapters and cables (I used a DVD-D to HDMI adapter with an old Apple TV and then my proposed hackintosh- DFI LanParty P55-36) I eventually realised (after five hours trying to diagnose what I believed was a bad connection of the pins on the female DVI!) my problem was with a DVI>DVI cable. For whatever reason it just wouldn't play ball. Fixed now, with the use of the DVI-D to HDMI adapter, hot glue was used to reduce cross-talk and 'lock in' connections on back of female DVI.



Furthermore: I've managed to power entire system with the native 190W PSU- the 20" Screen (down-converting 12V to 5V to enable 24V rail), one of the always-on 12V rails allows this, another 12V rail is unconverted by a PICO psu to power a 24pin and 4 pin socket on my DFI Lanparty P55-36, which is somehow powering a GT610, SATA, USB external HD too. Amazing.

AND- my noisy PSU is no longer high pitched... well... when the mobo is on. It still squeals when plugged in at the wall.

I think I'll attempt to downclock the i5 750 (2.67GHz) CPU and see if that will help the temperature which is going to be a bit of an issue IF I can even fit this mess into the G4's case.

Problems remain:

1. when I put the hackintosh to sleep, the backlight remains on (very faint glow)
2. the PSU, must be a grounding issue that the mobo is fixing. not sure how to diagnose
3. cpu downclock
4. the actual build!

Here goes...

Hi callumalden,

Glad to see you're up and running. When I was doing my TMDS -> DVI -> miniHDMI mod for my NUC, I had terrible artifacting any time I used any adapter. I see you've got yours sorted, but I wanted to share my solution. I used a direct cable - DVI to miniHDMI - an uncommon cable, but that's what StarTech is for. I've been running perfectly for almost a year. Just something to keep in mind in case you run across issues again. Looking forward to seeing your completed mod. You've inspired me to finish mine up.

-IC