Acorn BBC Master 128

The Master series of computers replaced the aging BBC Micro Model B AND B+ in 1986 providing more memory and flexibility than the BBC Micro whilst maintaining a very high degree of compatibility with both software and hardware that was designed to work with the BBC Micro. The BBC Master is widely regarded as the pinnacle of 8-bit home computing technology.

Expansions in this Master

This Acorn Master 128 has the following upgrades installed:

• Acorn Econet module
• RetroClinic DualOS
• Retroclinic Lithium CMOS battery backup unit
• IFEL Master ROM/RAM cartridge (not pictured)

Beeb@30

At the Beeb@30 event on the 25th of March 2012, this BBC Master was used to drive Dave Moore's Hybrid Music System and since that time, I've managed to build up my own Hybrid collection. You can see in the photo below the reasonably rare Hybrid 6000 sensor which is used with the SoundStage software to create music by sensing movement of a person standing in front of the device.

Repair/Change History

Upon acquiring this BBC Master, the machine was stripped down and the case was washed and cleaned thoroughly. The CMOS battery backup pack was replaced with a Lithium cell package from Retroclinic as it was found to have leaked. The composite video out socket was replaced with a new one due to an excessive build up of a black “tar like” substance. Finally, the output voltage of the PSU was reduced to 4.99v from 5.15v using the trimming potentiometer on the PSU.

On re-assembly and testing, it was found that the slow bus 6522 VIA chip (IC8) was failing and intermittently, the machine would not start. The original 6522 VIA chip was de-soldered from the board and a 40-pin turned pin socket was installed to aid ease of replacement in the future if the 6522 VIA chip were to fail again.

The MOS ROM socket was also replaced with a turned pin socket while the motherboard was out of the case to more reliably accommodate the RetroClinic switchable MOS daughter board. The switch for the switchable ROM was fitted to the underside of the Master near the Aux power supply.

On the second re-assembly, the machine started successfully and subsequent tests could be carried out which indicated that several keys on the keyboard were failing. The keyboard was stripped; cleaned and several key switches were replaced to fix several intermittent keys.

The original function key strips were recreated and are now in place.

Battery replacement schedule 

The battery was replaced in April 2011. The next battery change is due in April 2014.