cypherpunk said:
I don't believe you now. There is no hardware failure that should be able to generate gibberish text. Do you mean a screenfull of gibberish?
Better be careful in making absolute statements of fact, especially in the age of google.
http://www.computing.net/dos/wwwboard/forum/15564.html
From the guy who suggested how to fix the problem:
You also have to consider the possibility of a bad power supply (old machine) and noise on the +5v to the keyboard.
There is also the possibility of a bad AC ground wire. Computers need a good third wire ground. Going through a cheap extension cord will cause problems like that.
If you have a PS/2 mouse also plugged in, try unplugging it. They share the same power source (+5v) and it might make the problem go away. If it does, it does not mean there is a problem with the mouse.
UL requirements are that there be some sort of fuse or over current protection in the +5v that goes to the keyboard and/or mouse. I have seen films of very interesting fires that occur when you stick a small steal pin though a keyboard cable to simulate a short in the keyboard.
Cheap system board vendors just use a land pattern on the system board as a fuse. It just blows before a fire gets started. However "quality" vendors use a thermistor in the +5v line to the keyboard and mouse connectors (shared). This protects from over current when there is a short. And recovers to protect the next time it happens. (Cables get frayed and short out, it gets shorted plugging in a device with power on.) However, shorts tend to damage the thermistor and it becomes more of a resistor, that drops the voltage slightly to the keyboard as more current is drawn.
There is one very common symptom of low voltage to the keyboard. The system board controller "sees" random noise input that looks like data characters. The problem is worse when the mouse is also connected as it is drawing additional current through the damaged thermistor.
It takes a good volt meter and a device you can open up to probe the +5v levels. If it drops much and drops more when the second device is plugged in, you know what the problem is.
Normal solution, is to replace the system board. Difficult to find the correct type of thermistor. Some "techs" will connect a thin wire across the thermistor and "sell" it to you as a used replacement board.
