BBC Micro – An Update

As per the last post, my BBC Micro lived again, thanks to a replacement PSU. Unfortunately with more testing, it became obvious that it was unreliable. Some times it would boot to BASIC. Sometimes it would hang on a cursor prompt. Some times it would hang on an error about a Drive Fault and some times it would hang on a “File not found” error.

Now, I know the experienced BBC owners are screaming at the screen right now, because this was a clear case of PEBCAK. Turns out the BBC doesn’t like it when you have two different boot ROMs in it. I removed the DFS boot ROM and left the Turbo MMC ROM in there and it has worked fine since.

Next on the agenda was to modify the sound circuit. The BBC has an internal volume control, which is annoying to get to, so following a post on StarDot, I decided to make an external audio adapter. As this is a Mono jack, it’s possible to set it up such that when the external audio isn’t plugged in, the internal speaker works, and is disabled when you plug in the external sound.

I spent some time contemplating various solutions to mounting the audio, and I settled on using the unoccupied Econet port hole, as it had already been punched out somewhere in the distant past.

I got some spare sheet aluminium, and marked two circles a little larger than the Econet hole. I drilled a 6mm hole for the headphone jack to come out of in each circle, then carefully cut them into disks.

I then used a washer as an anvil and a large bolt as the driver, and shaped one of the two disks into a slightly concave shape.

Next up I made the adapter. One end plugs into the motherboard and the other plugs into the speaker, with the jack coming out the back.

There’s glue lined heat-shrink around the white adapter in the middle. I have fallen in love with the stuff.

After that I did a test fitting. Everything looked good.

I then cut a square of black PVC contact sheet out, punched a hole in it with a hole punch, and used it to cover the aluminium disk on the outside. In the end, I was very happy with the outcome, and it works very well, allowing the much cleaner sound of a pair of external speakers to be used.

The black PVC hides many sins.






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