MacTester57's HemiMac G4

[imarco88]

Since I'm getting rid of the DVI VEDID wire (I'm wiring the whole monitor to PSU) I'm having a probably stupid idea:
use DVI pin 15 (ground) or DVI pin 16 (hot plug) for grounding PSU PS_ON, in order to switch the PSU ON when a DVI source is connected and off when it's not.

Do you think this could work?

 

[MacTester57]

Since I'm getting rid of the DVI VEDID wire (I'm wiring the whole monitor to PSU) I'm having a probably stupid idea:
use DVI pin 15 (ground) or DVI pin 16 (hot plug) for grounding PSU PS_ON, in order to switch the PSU ON when a DVI source is connected and off when it's not.

Do you think this could work?

No, this will not work, because this is not a switched output. All your GND wires must be connected as straight as possible - they are the "0V reference level" of the whole system.

If you want to switch on your Pico PSU, if you connect a source to the DVI connector, you could use a transistor:
wire DVI pin 14 via an 1kOhm resistor to the base of a BC 548 transistor, the collector to PS_ON and the emitter to PSU GND

MacTester

 

[ersterhernd]

MacTester, I had some time this morning, so tore into iMac # 1 and switched the VEDID supply over from DVI 14 to PSU 3.3V instead. That leaves only one more machine to configure this way.

Both the iMac G4 and G5 work flawless with 3.3V to the pink wire of the LCD.


EDIT: Did the other 17" G4 too. All are 3.3V to the pink now, no issues and I'm breathing a little easier.


Cheers!

 

[MacTester57]

Hi Ersterhernd,
Thanks for the reminder. I will do this modification as soon I find some time :beach ball:

Just to be sure: did you wire the VEDID wire in parallel with the other three 3.3V LCD supply wires?

MacTester

 

[ersterhernd]

Yes MacTester, they're all soldered in the same cluster. Four 3.3V wires total...


Cheers!

 

[imarco88]

If you're going to open it, could you please check DVI Pin 14 (VEDID) Amperage? I believe I burned a transistor

At the end I installed a push switch button on the PicoPSU jump. My iMac as external screen works really good, but one day I will try to avoid this button switch

 

[MacTester57]

If you're going to open it, could you please check DVI Pin 14 (VEDID) Amperage? I believe I burned a transistor

Sorry, it's to late, I didn't see your post...

Update #397 Rewiring VEDID

First I would like to thank Ersterhernd for discovering this dangerous issue.

As you can see in the data sheet (if you have eyes ), this LCD panel needs a 3.3V signal on its VEDID wire (stupid). That means, that it should be wired to a 3.3V source on the PicoPSU instead of the common VEDID pin on the DVI connector.

The new pinout is the following:
- DVI pin 14 (5V) to inverter Pin 3 (red wire) and via an 1kOhm resistor to DVI Pin 16 (hot plug detect)
-VEDID to the LCD panel (red wire) soldered to the other three 3.3V LCD supply wires. All these 4 wires are connected to a 3.3V source on the Pico PSU

Removing the electrical tape:

The old wiring:

separating the VEDID wire:

Then soldered to the 3.3v source:

Re-applied shrink tube:

Works flawless so far...

I'm glad, that this potential dangerous issue is sorted out now.

MacTester

 

[MacTester57]

At the end I installed a push switch button on the PicoPSU jump. My iMac as external screen works really good, but one day I will try to avoid this button switch

This wiring should work fine for activating the Pico PSU, if you connect a DVI source:

Good luck

MacTester

BTW: please post some pics, if your MonitoriMac is finished.

 

[imarco88]

Thank you MacTester.
As soon as I will have some time to open it, I'll try again to put the transistor after DVI pin 14. I'm assuming I burned the last one because I forgot to place the 1Kohm resistor

I just noted that the iMac LCD does some lines when I wake it up from "sleep".
I mean: when the LCD source, a macbook pro, goes black (sleep) the iMac LCD goes black too, but when I wake the macbook pro up the iMac LCD does less than 1 second of coloured lines before waking up.

Of course this is not annoying, I was just wondering why this happens and if it is some kind of danger signal.

Here is a video to let you see.
[video=youtube_share;mE5jGYuHwPo]http://youtu.be/mE5jGYuHwPo[/video]

P.S. Shall I post pics in this thread or is it better to open a new one? My mod is so basic compared to yours and Ersterhernd's

 

[ersterhernd]

Hi imarco, my iMacs all do that, not as pronounced as in your video though. Just a thin line every so often.


Cheers!