Ivad sequence sent but display not showing anything about imac_g3_ivad_board_init HOT 2 OPEN

Hi, thank you for the high praise!

I'm in between meetings at the moment so I'll fire off a quick response that will hopefully help you and if not I'll give you a more detailed response later on tonight.

Everything you've done to power the iMac is correct, including bypassing the power switch.
However at least one of the I2C connections is necessary.

There are a pair of I2C buses we are dealing with in this project, the one that connects the arduino to the J20 connector (SDA_1 and SCL_1) and one that connects the arduino to the NUC via the VGA cable(SDA_2 and SCL_2).

The first one is absolutely necessary because that is the bus used to send the initialization sequence from the arduino to the IVAD board via the J20 connector.

The second one sends an EDID to the NUC via the VGA cable and is optional if you are willing to manually configure stuff on the NUC.

Without an EDID, the NUC has no way of knowing what the display capabilities of the iMac are so it's more than likely defaulting to a resolution and refresh rate that the iMac can't handle. If this is the issue, you can either connect a monitor to the NUC and manually force a resolution of 1024x768 @ 75Hz and then reconnect the NUC to the iMac or you can connect SDA, SCL and GND from the VGA cable to the arduino. Connecting the the second I2C bus is much easier.

Please let me know how it goes and good luck!

from imac_g3_ivad_board_init.

Hey, thanks a lot for the quick response. Absolutely no rush in this!

Regarding the EDID sequence, i had tried already to force the NUC resolution to 1024x768 at 75hz with another monitor and then turned off the Nuc. So assuming that the NUC stores the last settings, it should be sorted on that side.

Related to the IVAD/ EDID buses, there is an interesting fact. Basically the IVAD bus is the only one i’ve connected from the arduino to the J20 connector. Although i’ve noticed a discrepancy: for this bus i used PC4 and 5 from the arduino (same as per the wiring diagram you have in the main page. However after looking at the schematic for the J20 board i noticed in there you’re using PC4 and 5 for the EDID sequence instead, and PD4 and 5 of the arduino for the IVAD sequence. This makes me think that currently i’m sending the EDID sequence to the IVAD board??

I’m not home at the moment, but i will try to switch to the other bus from the arduino to see if that was the problem.

from imac_g3_ivad_board_init.