BBC Micro Model B with a Viglen ROM system

This BBC Model B is a relatively standard version with the exception of the addition of a Viglen Sideways ROM Cartridge system which can be seen to the left hand side of the keyboard with its dust cover fitted in place. The basic machine has an Issue 4 motherboard and an Intel 8271 disc interface fitted.

Beeb@30

I used this BBC Micro at the Beeb@30 birthday celebrations on the 25th March 2012 at ARM Holdings to interface with my VELA and run the graphing and analysis application that I developed.

Repair/Change History

On switching on the system, the disc interface would intermittently appear but was unreliable. After replacing all the disc interface logic chips and swapping out the 8271 controller, there was no change in the behaviour so a review of the Stairway to Hell forums indicated that there were a couple of other logic chips that should be considered suspect, those being IC24, a 74LS138 and IC26, a 74LS139. After replacing both IC24 and IC26, the disc interface became stable and reliable.

The Viglen Cartridge system was re-installed into this machine after replacing the 28 way IDC transition connector due to pin damage on the original part due to incorrect fitting by a previous owner. The ROM socket on the only cartridge PCB supplied was also replaced due to general wear and tear. An 8 way DIL switch was added to the keyboard for the ease of setting the computers initial configuration settings, finally, DFS 0.9H was replaced with the updated and unofficial DNFS 1.21 to allow for use of TUBE peripherals and 3.5" floppy drives.

I thought that I'd replaced the X2 Capacitors in the power supply in January 2011 but I hadn't. In December 2011, the X2 caps went pop and released their magic smoke. I actually caught the entire episode on camera...

The PSU was cleaned up and the capacitors were replaced as they should have been in January restoring the PSU to full operation.

In January 2012, the D7002 ADC chip that controls the analogue port failed and was replaced.