[Help Needed] My work on an Apple Studio Display M7768 (The Transparent ADC CRT)

[Titania]

Hello all.

I bought an M7768 Studio display, after looking at many videos and articles about it, with the intent of adapting it to use with modern systems. Using the example of the existing ADC converter boards, but lacking access to an ADC female plug, I instead opted for opening the cable, studying the pinout, and splicing the corresponding Power, USB, and VGA cables. Using a tester, I was able to map out the internal wires to the pins, creating the following diagram:

Following this, I wired power to a DC plug, to connect to an external PSU, USB to a standard USB cable, and the remaining video and DDC wires to VGA. Using this, with a Windows/Linux PC I could:

• Detect the monitor and brand/model/year data.
• Download the EDID for it (Attached to this post)
• Use ddcutil over USB to look at the configurations for the device.
• Use ddcutil over USB to trigger the degauss (can hear the click noise)

However, I cannot use the monitor, as it still will not display unless it gets some sort of wake-up signal (probably over DDC) that only G4/G5 era Macs will output.

This is why I'm asking for help, if someone could dump the wake-up signal this monitor requires, it may be possible to replicate it on Linux (and potentially windows), thus allowing these monitors to be usable on modern devices.

 

[Kai Robinson]

First of all, welcome to TinkerDifferent!

I believe @fehervaria may be able to help on this, he's done some work on adc to hdmi before.

 

[François]

Why not buy a base model PowerMac G4 with ADC? You may be able to find one for cheap, and it will help you tremendously in your reverse engineering effort. It’s not the first time I’ve seen someone willing to use this monitor on a non-ADC computer, and it seems to be very difficult (no one has figured it out, AFAIK).

All the settings for this monitor are done in software, the base settings like brightness, and the geometry settings, so a new software has to be written for the targeted OS, and I’m pretty sure that the communication between the Mac and the ADC CRT is non standard and has to be reverse engineered. (why would Apple engineers bother with the constraints of the DDC standard when this monitor would never be plugged in a standard VGA port)

 

[François]

Thinking out loud, maybe the Linux guys figured it out? At least on the software side? Is there a Linux distro for the Mac that properly handle this monitor? With a software that allows you to change all the settings? Looking into the code will then allow you to figure out the protocol and maybe even the proper initialization for the monitor.

Or maybe the monitor initialization at startup is done in firmware, or is a simple hardware trick…

 

[Titania]

All the settings for this monitor are done in software, the base settings like brightness, and the geometry settings, so a new software has to be written for the targeted OS, and I’m pretty sure that the communication between the Mac and the ADC CRT is non standard and has to be reverse engineered

Thinking out loud, maybe the Linux guys figured it out? At least on the software side? Is there a Linux distro for the Mac that properly handle this monitor?

While AFAIK no distribution handles it, the settings are handled through DDC over USB, Linux can do it with ddc-util and similar tools. These things are actual standards that have existed for a long time, but never got consumer-facing adoption. Cinema Displays, and the G3 era Studio Displays, both used it to implement their OS-based image controls.

DDC over VGA has less luck, as it doesn't report a valid version. However, even without it, the DDC protocol works over an i2c bus, that can be controlled arbitrarily on Linux, such that outputting any command isn't unlikely.

It’s not the first time I’ve seen someone willing to use this monitor on a non-ADC computer, and it seems to be very difficult (no one has figured it out, AFAIK).

From my own investigation into the issue, this is partially because of the lack of proper information sharing; before opening the cable, I had never found any information on what wires it had or how they were configured, for one. The fact that DDC over USB could be used I found out via a github issue on an obscure repo, etc.

Why not buy a base model PowerMac G4 with ADC? You may be able to find one for cheap, and it will help you tremendously in your reverse engineering effort.

Finding working ones at a reasonable price ain't that easy over here. That, and I wouldn't be surprised if this ends up needing a Logic Analyzer (which I also don't own), as from tinkering in a VM, it does not look like OSX is willing to output what it does over DDC. The hope was that perhaps someone had the setup to provide this info. Going by the eMac and iMac conversion projects, which also deal with a wake-up signal on a CRT, it seemed like a number of fellow tinkerers have taken to analying the inner PCBs of working CRTs, and this should be considerable simpler (just the outer cable).

 

[Kai Robinson]

Where are you based? I can rustle up a cheap G4

 

[François]

Everything has been figured out, except for the startup sequence? That is very unfortunate!

 

[Titania]

Everything has been figured out, except for the startup sequence? That is very unfortunate!

Yep, that's why I hope this can be solved; it's the last piece of the puzzle to free these monitors.

 

[wottle]

Hello all.

I bought an M7768 Studio display, after looking at many videos and articles about it, with the intent of adapting it to use with modern systems. Using the example of the existing ADC converter boards, but lacking access to an ADC female plug, I instead opted for opening the cable, studying the pinout, and splicing the corresponding Power, USB, and VGA cables. Using a tester, I was able to map out the internal wires to the pins, creating the following diagram:

View attachment 10144

Following this, I wired power to a DC plug, to connect to an external PSU, USB to a standard USB cable, and the remaining video and DDC wires to VGA. Using this, with a Windows/Linux PC I could:

• Detect the monitor and brand/model/year data.
• Download the EDID for it (Attached to this post)
• Use ddcutil over USB to look at the configurations for the device.
• Use ddcutil over USB to trigger the degauss (can hear the click noise)

However, I cannot use the monitor, as it still will not display unless it gets some sort of wake-up signal (probably over DDC) that only G4/G5 era Macs will output.

This is why I'm asking for help, if someone could dump the wake-up signal this monitor requires, it may be possible to replicate it on Linux (and potentially windows), thus allowing these monitors to be usable on modern devices.

FYI, I know it is probably too late, but you can get some really cheap ADC graphics cards and harvest an ADC connector from those.

 

[Titania]

FYI, I know it is probably too late, but you can get some really cheap ADC graphics cards and harvest an ADC connector from those.

I don't have a soldering station to handle the extraction and re-soldering of those; part of my project was figuring out what's the "least tools" needed way to adapt this monitor, now that I can share the cable color code, someone could feasibly do this with only a soldering iron and a wire stripper. If you wanted to keep compatibility with ADC, you could use the opposite end of the cables to make an inverse adapter.

All that's left is figuring out the boot.

 

[luminescentsimian]

Hmm, I wonder if the init code could be divined by examining the ROM of an compatible video card using something like https://github.com/openbios/fcode-utils . The ROM might define a set of DDC/I2C OpenFirmware commands that then might be possible to look at what data they're called with.

 

[Titania]

Did some more research on Archived PDFs:

• The Service Manual for the Monitor reveals there was a VGA conversion board for the CRT.
  • It also shows the monitor could be booted by a Video Signal Generator with a specific firmware.
  • It also notes that, if not turned off by the same VSG, it could alter the monitor's behavior, ( power draw on idle, degauss on wakeup). Perhaps implying that the monitor has "modes" that could be set via i2c.
• The manual for the older 17'' and 21'' CRTs lists them as supporting VESA DDC 2B.

 

[luminescentsimian]

How far did you get with this? I just got my hands on one of these and have a G4 I can use to poke at it. Looking at the service manual and looking up the Quantum signal generator I don't think the signal generator knew anything about DDC or any sort of bi-directional communications.

 

[Titania]

How far did you get with this? I just got my hands on one of these and have a G4 I can use to poke at it. Looking at the service manual and looking up the Quantum signal generator I don't think the signal generator knew anything about DDC or any sort of bi-directional communications.

I actually managed to make it work, and have been using it as a daily driver, but I had to obtain a functioning G4 to do the booting.

I made a couple of discoveries regarding the monitor:

• While the monitor needs a specific startup signal, and lacks any off button, it will switch to a low power mode if it stops getting a video signal. This means it's actually easy to use as a regular monitor, as long as you don't unplug it from mains, once your PC goes on standby, so will the monitor.
• The monitor's parameters can be controlled over USB, using DDC over USB. On Linux, this can be done with ddcutil, on Windows, I had to setup a specific Linux kernel with WSL2 and USB passthrough to do it, as AFAIK no tools exist.
  • While I could not test some non-standard fields it has, I can confirm that it's possible to control geometry and brightness/contrast using these. The information here applies to this monitor.
• I haven't been able to figure out the bootup, as I lack a signal analyzer setup, but I noticed that the monitor performs a degauss-and-boot before MacOS fully loads, as for some reason, the G4 I obtained shuts down during boot while the display is connected.
• Additionally, I can confirm:
  • The boot signal works over the DVI port with a DVI-A/VGA converter, so it's not something specific to ADC.
  • The boot signal does not require an USB connection to the monitor.

 

[_AP]

I am also interested in doing some sort of conversion. A did see a youtube video where someone used jasondoesitall board and could get it to work on a PC. I don't know if he used a powermac for boot.

I would like to fashion something, somehow to get this to work on a BeOS/Haiku machine that dual boots with Windows XP. I have a PowerMac G4 with upgraded ADC card, but it doesn't work and I don't think it will without having one that shipped with an ADC card. Also, I don't want to have to do the switch. I am good with troubleshooting, but not very electronically inclined. I can attempt soldering though.

I'll start by sourcing components for the jasondoesitall adapter and maybe that will just work. How many volts should I do? I've seen conflicting 28v vs 25v options.

I appreciate any help, and if I get this working in the meantime I'll report back.

 

[_AP]

I ordered the boards and the ADC connector. I had a question about this diagram. Could someone who knows more about circuit boards than me tell me what resistors, capacitors, diodes, I would need? I can almost make it out, but want to be sure before i order. I had a couple more questions.
- What goes in the spots labels VGA, USB, ADC Pwr.
- There are 4 holes in capacitor area for the 10uf/30v capacitor. Am I only using two holes and there are different holes for different size caps?
- What voltage power supply should I use if I am going to attempt and apple ADC CRT.
- On the left side, are those both for USB, and can I just solder one of the options on there? (USB 2.0)
- What is that arrowy unlabeled thing above Tip (+)
- What are all those little holes unlabeled on the board?

I did look at schematic and did email him. I'll call him if he doesn't get back to me, maybe I got spam-filtered.

EDIT: I assume DC capacitors? What kind is best considering the fact that I want it to have the best quality I can.

 

[_AP]

I was able to get this to work with an Apple ADC CRT.

First I gathered the parts. Don't go doing what I did and get 10w resistors. 1/4 w resistors were absolutely fine and the right size.

I didn't use any of the LED stuff. I used the parts listed (different DVI connector, they didn't have one listed)

- DVI: Mouser #538-74320-9010
- VGA: Mouser #636-181-015-213R171
- ADC: DV3R035N11 (Surplus Sales of Nebraska)
- USB: #538-105017-0001 (Untested, not sure if I soldered it correctly)
- DC Power: Mouser #710-694106301002 (Wurth Elektronik) (Higher Power rating as it's a CRT)

1N4004 diode (Jason says 1N4009 but I didn't have)
1,000 OHM 1/4 axial resistor (best quality possible)
50v 100uf Capacitor: Mouser #647-UBW1H101MPD1TD
35v 100uf Capacitor: Mouser #647-PLX1V101MDL1TD

Both worked. I would use any nichicon (Jason recommendation) with 35-50V with 100-150uf rating.

LHV-24050 Power adapter 24v 5A. (Same power ratings should work, this one had right size plug. You may want to order the correct size plug from mouser)

Soldering was not as bad as I thought it'd be. I did two boards. You will definitely need flux. I used chip-quik smoooth-flow something or other. I also had alcohol, toothbrush, and paper towels handy to clean up extra flux. What a mess!

Then I tested them. They both have the same issues.

1: As others have found, it will not display without a boot signal from a PowerMac. Intel macs didn't work.

2: I have a PowerMac G4. It didn't come with ADC. I put a card with ADC in it, but the ADC port doesn't work with the monitor. However, when I plugged it into the VGA port, before booting (with the ADC adapter) it worked.

3: I was then able to plug it into the intel mac, and it worked.

4: I tested two intel macs, with both boards. They both have only the 2 resolutions that others have had. They both have a green hue to everything. The PowerMac had the same green hue I believe. I will do more testing though.

5: I didn't test USB. It was not required for the display to turn on.

The things I will try to resolve, and would appreciate any hep in, are:

A) The green hue. (I'll try WinACD, unsure never used it.

B) Needing a PowerMac to boot. It must be some VGA signal, but I wouldn't know where to start.