Anyone interested in VGA/DVI to ADC adapter?

wottle

Active Tinkerer
Oct 30, 2021
526
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Fort Mill, SC
I know Apple has a DVI to ADC adapter / Power supply. I know of (and own) the Dr Bott's DVIator for connecting a computer with DVI out to an ADC monitor. The problem is, they only support digital signals, which means you cannot use them to connect a more modern computer to the best of all ADC monitors, the 17" Studio Display CRT!

That CRT expects an analog signal, and both Apples adapter, and Dr. Bott's only support DVI with a digital signal.

However, I found people who have worked on holding this problem before, as well as a user on Reddit who claimed to have used one of these solutions to connect VGA / DVI to his ADC CRT. This is the adapter in question: https://www.jasondoesitall.com/adc/

No work on it recently, but I figured the ADC pinouts haven't changed, nor have USB, VGA, or DVI. So I ordered a 3 pack of PCBs off Oshpark (https://oshpark.com/shared_projects/tUQ9np4l), the ADC connectors (search for "(CPC) DV3R035N11" on https://www.surplussales.com/Connectors/Video-Data.html), and then the VGA, DVI, microUSB, and DC power connectors off of Mouser (cart: https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=40B2BB6866)

You need a handful of other parts, although I think the only other required component is a 1k resistor. All the other resistors, diode, capacitor, and LEDs seem to be optional.

Anyway, I finally got all the parts and PCBs in and soldered everything in place. I plugged into my 24v power supply, connected the ADC connector to one of my LCD Cinema displays that I don't care much about (just in case I've done something horribly wrong and it seemed to be working. The LCD's power button lit up, the ADC, VGA, and USB lights lit up when I plugged the DVI output of my TiBook into it, and ran a microUSB cable to the TiBook. When I power on the TiBook, the screen on the laptop turned on ,as did the Cinema Display (success!!!). Sadly, a few seconds after this, the laptop shuts off without warning. It does this every time I try to boot. I get a brief gray screen, and then the laptop powers off. I tried similarly with a Quicksilver PowerMac G4 (which has an ADC connector, but I used the DVI out. After a brief boot, the machine shuts down.

I did some digging into ADC pinouts (https://developer.apple.com/library...doc/uid/TP40002012-CH207-DontLinkElementID_21) to see if there were any problems with my soldering. I only found one issue, and it appears to be a problem with the PCB. On the PCB, pin 15 on the DVI connector was connected to pin 56 in the DVI connector. Whereas on Apple's specs, pin 15 for DVI is supposed to be connected to ground.

So, I was hopeful that was the issue, I cut the trace between pins 15 and 6, and ran a bodge wire from pin 15 to ground. Plugged in my board, lights looked good, but I still have the same behavior - brief moment of an image, followed by nothing.

I did plug it into my 17" Studio CRT to see if the behavior was different, and it was - it would not even turn on the CRT. Maybe my 24v power supply is too week, or maybe there's another issue.

So, that's where I am at. Is anyone else interested in trying to figure this out and providing others with a working solution to use those old ADC displays that we all have lying around? I'm afraid I'm at the end of what I can thing to try, so someone with more of a background in this might be able to help me know what to try next. Any help would be greatly appreciated. And once we have a working solution, I'll gladly put all the info together here so it will live on if JasonDoesItAll's blog goes away, or the Apple page gets removed.

Also, because I didn't want to short anything out while testing my 24v 4A device, I made a modified, 3d printable altoids tin like container to house it and keep my bodge wire safe. https://www.thingiverse.com/thing:5526854
 

François

Tinkerer
Aug 9, 2022
90
39
18
France
You should check the wiring of the board against your DVIator. AFAIK, a DVI to ADC adapter is just straight wiring of the DVI, USB & power lines to the ADC connector.

As to VGA to ADC, this one is (very) complicated. IIRC Apple cheaped out on the 17" Studio Display CRT by not implementing (completely, correctly?) the DDC protocol. Communication between the Mac and the 17" Studio Display CRT seems to be done over USB. The 17" Studio Display CRT uses VGA signals, but is not a VGA monitor. Maybe using a microcontroller between the computer and the 17" Studio Display CRT you could present the correct DDC protocol to the computer and send to the 17" Studio Display CRT what it is expecting. But AFAIK this is not documented at all and would need to be reverse engineered.
 
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wottle

Active Tinkerer
Oct 30, 2021
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Fort Mill, SC
Ah, I didn't realize that and thought it simply used the analog pins (blades) on the DVI connector to send an analog signal.

There's a user on reddit claiming to use his ADC CRT with the adapter board I made to run the ADC CRT off his Mac Pro ( https://www.reddit.com/r/VintageApple/comments/wz704t/_/imb33ea ). I don't believe the Intel Mac Pro ever came with an ADC compliant video card, using VGA out to drive the monitor. Still trying to replicate his results.

Additionally confusing is how much is going on in the Apple DVI to ADC adapter. If DVI is simply passthrough for the key DVI pins, plus something to inject 24-28v power, and split out the 4 pins for usb, what is the board doing? I think the DVIator is simply the passthrough approach, with breakout cables for the 24v input and USB. I'll try to do the pin comparison between my adapter and the DVIator at some point. However, given I am really looking to use the VGA functionality for my CRT, I really don't care as much about the DVI pins.
 

fehervaria

Tinkerer
Sep 23, 2021
153
160
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North Germany
3/4 year later... I just find your topic @wottle
Did you had some success?
I developed an adapter board to connect HDMI output to ADC Acryl Cinema Display. What I learned during the project is to make sure your external power supply gives enough power (amperes) to your monitor!
I use/set mine PSU to 27V (as the Apple PSU from a G4 PowerMac gives 28V).
Here we are talking about: Post #10
 

ShadeDream

New Tinkerer
Feb 5, 2022
8
3
3
Austin, TX
I have some of the PCBs and connectors with plans to build at least one out eventually... needed to source a power supply (and connector for it) still along with some other little bits to build it. I couldn't find a clear easy option for the power connector they suggested so I haven't really gotten around to trying to figure out a solution on my own. This stuff is not my specialty and I don't want to kill my ADC CRT in the process... so it's been on the back burner.
 
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