Microvitec Cub Repair Tools
I've been helping out at The National Museum of Computing (TNMOC), specifically recapping and repairing the classic Microvitec Cub monitors. The Cub was very widely used in British schools in the 1980s (paired with BBC Micros) and TNMOC use them in their retro computing classroom.
Note that working on CRT monitors like the Cub is potentially fatal and that you proceed at your own risk. Do not touch anything inside the Cub unless you are certain it is powered off and that all parts that can store charge (including the tube and the capacitors) have been discharged.
This page explains some tools that I've built to make working on the Cub easier
The first thing you are going to need to test a monitor is a pattern generator. One option is to just use a BBC Micro, or you can buy compatible pattern generators 2nd hand from EBay. I wanted something smaller and ideally battery powered to make it easy to do quick tests and not need lots of desk space and wires.
I developed a small RGB pattern generator based on the Raspberry Pi Pico. For details see the Git Pico-Pattern project:
- Pico-Pattern: GitHub or Local mirror
Replacing components on the Cub means removing the main PCB and working on the bottom of the board. As the PCB has many tall, fragile, components it is easy for these to be damaged if you just work on the PCB without supporting it off the desk. I designed a Jig to hold the PCB.
To make the jig you will need the following components:
- One piece of 12mm ply cut to 310mm x 90mm
- Two pieces of 12mm ply cut to 210mm x 90mm
- A method to join the ply at right angles (e.g. "locking joints" used for kitchen cabinets)
- Four 3D printed brackets to hold the PCB (two short and two long)
- A 3D printed centre support for the PCB
- Suitable wood screws
Start by preparing the ply components and construct a plywood frame shown below. I haven't measured the exact width, so I recommend you fix one side of the frame and then dry-fit the 3D printed parts with a real PCB from a Cub to get the precise position of the other side.
Make the 3D printed parts from these files. I used PLA and printed them on their side with support to the bed only. This isn't the prettiest arrangement, but it is stronger than trying to print them upright.
Put the two pairs of brackets along the sides of the plywood frame. Put the short brackets at the back and the long brackets at the front. Set their positions with a Cub PCB and then secure with screws.
Put the centre support near the centre of the back of the frame. Place it so it will be on the empty part of the PCB near to the power transistor with the PCB both ways up. Secure with screws.
Back Panel Bypass Leads
One annoying thing about working on the Cub is that the main board needs to have connections for power, signal and contrast to the back panel. This can be rather awkward to layout if the monitor is open. To help I have made simple leads that provide an alternative to the back panel to provide contrast and signal in. The Cub PCB has standard 0.1" headers for these connections.
I would like to do something similar for the power lead too, but the connector used by the Cub is no longer available I don't have an idea for a way to make a substitute. Let me know if you have ideas.
Discuss these tools and other information about the Cub in this Stardot thread.