17-06-2026, 09:54 AM
The keyboard is scanned by the 6545 CRT controller, so the PIO being out of it's socket will not affect the keyboard.
It's rare, but not impossible, that all the keys are faulty. You can check the 'On' resistance of each key with a multimeter.
For a key to register the ON resistance should be lower than 100ohms. There are 2 types of key switches used in these models - the early
production units used a switch with a black shaft (that the cap sits on) and later a white shaft. Although different inside, they are
both carbonised rubber on metal switch plates designs rather than metal on metal. Sadly, over time, the rubber deforms and becomes
brittle, and the metal plates tarnish.
A simple way to check if the keyboard circuit is working is just to short the contacts of one of the switches to see if the key press appears
on screen.
In terms of display stability, it sounds like you are using a reasonably modern TV with it's AV input at a guess.
Most (post 2000 era) TVs have trouble syncing with the Microbee's mono video composite output and what you are seeing is most likely
just that incompatibility.
It's rare, but not impossible, that all the keys are faulty. You can check the 'On' resistance of each key with a multimeter.
For a key to register the ON resistance should be lower than 100ohms. There are 2 types of key switches used in these models - the early
production units used a switch with a black shaft (that the cap sits on) and later a white shaft. Although different inside, they are
both carbonised rubber on metal switch plates designs rather than metal on metal. Sadly, over time, the rubber deforms and becomes
brittle, and the metal plates tarnish.
A simple way to check if the keyboard circuit is working is just to short the contacts of one of the switches to see if the key press appears
on screen.
In terms of display stability, it sounds like you are using a reasonably modern TV with it's AV input at a guess.
Most (post 2000 era) TVs have trouble syncing with the Microbee's mono video composite output and what you are seeing is most likely
just that incompatibility.