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Apple ADC Monitor to Macintosh II?

Concorde1993

Well-known member
Two weeks ago, I decided to take the plunge and purchase a NIB Gefen DVI-to-VGA adapter on eBay. It arrived today, and of course, I've got problems.

Firstly, my ADC monitor remained blank, even after the IIfx completed its RAM test (and this was with the 8.24GC Card). Adjusting the Gefen's EDID switch from Internal to External and vice-versa yielded nothing. More seriously, I noticed a strong electrical smell from the Gefen, so I promptly shut everything down. Fortunately there was no smoke, but even three hours after conducting this maiden test, the Gefen still has a pungent electrical scent.

But we're not done yet.

Now the ADC monitor refuses to display anything - all I get is the bright solid Power Indicator lamp that now immediately powers on and stays on when the monitor is connected to an outlet. Swapping ADC-to-DVI adapters made no difference (I have two). Zapping the PRAM on my B&W leaves me with the same result. Did the Gefen fry something in the ADC monitor? My IIfx was not hurt at all during this experiment.
 

beachycove

Well-known member
I think we have to assume that pungent electrical burning smells are not a feature of the box you bought, so BAD things may well have happened. As for the dead ADC, those things are delicate flowers at the best of times. Do you have a G4 or the like to test it with?

Take it apart and see if something obvious has blown would be my advice. I did once fix an ADC that had a burned component just beneath the rear casing/ covers. Long time ago, though, and details are foggy, but it worked afterwards. I scavenged parts from a broken display I found at a recycler.

On the general question of digital versus analogue signals, and the incompatibility thereof, how does one of these work then? It’s not doing any conversion, surely: https://www.amazon.ca/Griffin-Technology-ADC-Video-Adapter/dp/B00009MF7Z
 

Concorde1993

Well-known member
Do you have a G4 or the like to test it with?
Just turned on my B&W (it has a G4 PCI board). The ADC monitor lives. I guess leaving it unplugged for a few hours cured whatever ailed it. Let's see how long this lasts.
On the general question of digital versus analogue signals, and the incompatibility thereof, how does one of these work then?
I have one of those adapter cables (forgot the brand - probably Belkin) but it's ADC to DVI. It poses the same problem as the Griffin adapter since the ADC portion is male and I would need a female end to complete the transition. From what I've seen online, no company produced an ADC female to male DVI adapter (Apple's own monstrosity excluded).

With that said, I'm calling it quits with this project. Currently working with the eBay seller to get a refund on the Gefen. It sucks I'll be stuck with a two-monitor system until I can find a monitor that will work with all three desktop Macs (IIfx, Mac Pro 1,1 & the B&W). My Electron III poses the same problem as the ADC monitor - it works with the Mac Pro 1,1 and B&W, but shows a dark green tint when connected to the IIfx. My Electron IV was just the same before it started showing signs of death - it worked with the 1,1 and IIfx - but not the B&W.

But I guess two out of three ain't bad, right?
 

Melkhior

Well-known member
@beachycove The Apple Display Connector (ADC) is a superset of the full DVI connector; it carries both the digital signaling and the analog signaling that makes full DVI compatible with VGA trivially. So if you want to connect a DVI or VGA display to an ADC source, you just need an adapter with the proper wiring, and it can ignore the extra signals. Very simple.

On the other hand, if you want to connect an ADC monitor to a non-ADC source, then you need to supply enough signals for the monitor to work, which in addition to the digital DVI signals will include at least the power supply, probably the soft-power, but probably not the USB stuff or analog signaling. That's why the Apple adapter is such a clumsy thing, it needs to supply 100W @ 24V to the monitor - it's effectively a power supply for the monitor that happens to also provide DVI pass-through from the DVI input to the ADC output...
 

Concorde1993

Well-known member
You've clearly given it a bit of a workout, how could you justify a refund?
The Gefen was advertised as working. Obviously it isn't. Why should I hold onto something that doesn't do the job as intended and poses a potential fire hazard?
 
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