Acorn BBC Micro Model A

This is an early "Issue 2" BBC Micro Model A that has been upgraded at some point to full Model B specification. The easiest way to tell that a Model B was previously a Model A machine is simply to take a look at the solder side of the motherboard paying particular attention to the where the connectors are soldered onto the board. The difference between hand soldered and machine soldered components is quite obvious.

Acorn BBC Micro Model A upgraded to Model B specifications

The Issue 2 motherboard of the BBC Microcomputer is significantly different to the later Issue 4 and Issue 7 motherboards and provides circuitry that is capable of terminating and also providing a clock signal both for an Acorn Econet. There are several other differences but the majority of those changes are simply refinements to or fixes for the existing hardware of the BBC Microcomputer. The changes to the Econet circuitry however were quite major changes to the design and their removal in subsequent revisions made the configuration of an Econet network much more flexible as those functions were replaced by peripheral hardware devices.

Repair/Change History

The PSU X2 Capacitors were replaced in January 2011 as they had already blown. An ATPL ROM board was removed and some soldering work on the motherboard was tidied up.

A 2 way DIL switch was replaced by an 8 way DIL switch on the keyboard for the ease of setting the computers initial configuration settings.

An 8-way DIL switch soldered onto the BBC Micro circuit board provides an easy method to change configuration settings

The two missing 3M "Bumpon" feet on the bottom of the case were replaced.

In April 2016, I sourced a second ATPL Sidewise ROM board which I fitted to restore the machine to the specification it had when I received it in 2011.

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Acorn BBC Micro Manuals

Whilst the BBC Micro Service Manual is useful, RetroClinic produce a fully revised and updated Service Manual that covers the BBC Micro A/B,B+,Master and Master Compact which you can usually find for sale on ebay.

BBC Micro maintenance

Further information

The BBC Micro case was designed by Allen Boothroyd

Here are some links to further information and resources for the BBC Micro that may be of interest.