A PDP 11 by Any Other Name: Heathkit H11 Teardown and Repair

[Lee Adamson] is no stranger to classic computers. He recently picked up a Heathkit H11A which, as you might remember, is actually a PDP-11 from DEC. Well, technically, it is an LSI-11 but still. Like a proper LSI-11, the computer uses the DEC QBus. Unlike a lot of computers of its day, the H11 didn’t have a lot of switches and lights, but it did have an amazing software library for its day.

[Lee] takes us through a tour of all the different cards inside the thing. It is amazing when you think of today’s laptop motherboards that pack way more into a much smaller space. He also had to fix the power supply.

We are looking forward to seeing more videos on this computer. We miss the days that your computer broke down into multiple boards plugged into a backplane. Even though the computer is a Heathkit, the CPU board came from DEC assembled. However, Heathkit had its own boards that you did build along with things like power supplies.

The power supply needed some care, as you might expect. A diode wasn’t attached properly but it wasn’t clear if it had been damaged in transit or if it had never been installed correctly. Replacing it put the power supply right and now he’s ready to see if the thing will start up.

There are plenty of ways to emulate a PDP-11 on things like Arduinos. If you want to see what assembly language looked like on this machine, there’s a tutorial.