ColorSync Monitor ADB problem

[beachycove]

I have had for a few years a 20" ColorSync monitor from c. 1997 in which the included ADB ports do not work. On a ColorSync, a failed ADB port is worse than it sounds, because it is not possible to use the appropriate software utilities to adjust brightness, etc., without a functional ADB port. The monitor, alas, needs some fine tuning after all these years (though usable in the right light, it has become very dark), fine tuning that I am unable to perform because of the failed ADB. The brightness button on the front of the monitor, which kicks into action when the software extensions are disabled, has been used to push the brightness up as far as it can go, which isn't very far. There are no pots around the back or under the plastics that allow further adjustment to be done manually on a ColorSync; such adjustment has to be done by software.

To fill in some of the details, what happens when the proper software for the monitor is installed (AppleVision/ ColorSync) is that I get an AppleVision error message on startup telling me that I do not have an ADB Cable plugged in (when I do). This happens in system software from 7.x right through to 9.x. I am instructed to check the cable connection and reboot. Oddly enough, power on works through the ADB port (since the keyboard is connected to the monitor's internal ADB and the monitor cable includes an ADB plug which goes to the machine). The only remedy for this error message is to disable the AppleVision software via the Extensions Manager, though the error message can also be by-passed and the machine used — since this is not a system crash.

I have replaced the ADB board in the bottom of the machine with one scavenged from a 20" AppleVision monitor (the same animal before the rebranding to ColorSync). No joy. Symptoms are identical.

There is nothing about this in the Service Manual. Is there anything obvious that I could try? Fuses? Laying on of hands? Fasting and prayer? These were absolutely top of the line monitors back in their day, and I would very much like to get my 20" ColorSync working properly.

 

[Bunsen]

I have replaced the ADB board ... No joy. Symptoms are identical.

That really is odd. I assume you've tried another ADB cable, and a different Mac? It could be as simple as a broken or loosely soldered pin on the ADB receptacle, or some other mystery.

 

[beachycove]

Thanks for replying. It is odd. The monitor also has been tried on many machines, with the same result.

The monitor cable on these includes an ADB cable (the cable splits about a foot from the end into DB15 and ADB), and I have in the past been inclined to wonder whether the cable may be defective. However, there are two separate ADB plugs on the base of the monitor, and on connection of two ADB cables, one to the monitor from the keyboard and one from the monitor to the machine (in order, in theory, to by-pass the ADB cable that runs into the innards of the monitor), the same symptoms present. I assume that this means that something inside is awry.

Odder still is that, through it all, ADB peripherals such as Mouse, Wacom Drawing Pad, Kensington trackball etc. seem to work just fine. However, I have the AppleVision error, with attendant problems as described. I have also taken great pains to install proper System software; the trouble does not lie there.

Unfortunately, I am afraid to go in there to tinker, as not only does it look excessively complicated, but a) I have no schematics; and B) whereas ordinarily I might take the chance with soldering iron and take it on the chin if I got it wrong, I am in this case frankly afraid of the very considerable electrostatic potential stored in a 20" ColorSync. Electronics ignorance and one of these beasts do not make for safe play.

More modestly, is there some way of testing the various wires in the ADB connector with the monitor turned on?