16-08-2020, 08:45 PM
By coincidence, I spent a bit of time working on my BBC Micros a few weeks back.
I normally have a BBC Master set up in the office, and the kids like to play an occasional game or two. I sometimes like to dig out something from the past - sometimes just for fun, sometimes for real, as it were. But I decided that I needed to pack it all away to make space for another PC. Before doing so, however, I needed to resurrect my old model B to print out a couple of diagrams that I did back in school. The software wasn't compatible with the Master.
The PSU in the model B had a label saying that the -5V rail was missing. I'd written that when I thinned down my Acorn collection, about 10 years ago. I think the PSU came from another machine, and I took the good one from this model B to help out the person taking away the chosen machines. No problem - just a case of changing a diode on the secondary side. While it was apart, I replaced the two RIFA caps on the mains side, and the electrolytic on the primary side that always causes problems. I then found problems with compatibility with my disc drives. I wondered if it was because of having version 0.9 of the DFS installed, and that prompted me to dig out my EPROM programmer, along with the Windows 98 machine needed run it - the usual sort of "rabbit hole" old computers send you down...
In parallel with that, I decided to try my B+ machine. This worked perfectly, but - you guessed it - after about 5 minutes, one of the RIFA caps let go! Ironic, given that I had just refurbished the other PSU, which hadn't yet blown its RIFAs. Still, no harm done, and refurbing the B+ PSU was obviously a good thing to do.
Trying the software, I found that although it wasn't compatible with the Master, it was OK with the B+. So time to hook up the Epson dot matrix printer, complete with new ribbon, and try to remember how to drive the software to get the print-outs. That all worked well after I found an ancient photocopy of the user instructions. Job done.
Meanwhile, I'd made a DFS 1.2 ROM for the model B, and it appeared to work as a ROM, but I was still having disc issues...
I remembered that I had another model B - a really tatty one that was missing its PSU. It had been modified to be used as a VT clock, so had a genlock card fitted - not an easy mod. I decided that perhaps now was a good time to bring this back to original spec, so I carefully removed all the mods. That was easier said that done, and there were a couple of things that took a bit of time to sort out - nothing worth relaying here as it's unlikely anyone else would run into the same problems, but it certainly took longer than it should! But once working, I took it upstairs to try in the office, and had exactly the same disc issues!
So I dug out another drive from the attic, and the problems all went away! So no need to have attacked the modified B, but at least that's behind me now. If I find another PSU - and ideally another case - then I've got another working machine. I think the problems were a compatibility issue with the newer drives in my setup upstairs (which would have been sold as drives for PCs, but can be made to work with some(!) BBC machines with the right link settings) and the earlier 8271 controller chip. The B+ and onwards used the 1770, which is definitely happy with these later drives (decent ones, made by TEAC).
So anyway, if you haven't already changed those RIFAs, I'd definitely recommend doing so.
I would be cautious about running them up on a variac though. Some switched-mode power supplies don't like that
I have a couple of Masters, but have never been inside their PSUs. I believe they also contain RIFAs though. Checking them out is on my to-do list...
One of my Masters was bought brand new. Though that was in 1996! During school, I desperately wanted a BBC micro, but there was no way we could afford one - plus all the peripherals needed. They were hugely expensive for even the well-off kids, let alone the likes of me, living in a council house. I was allowed to borrow one from school during the holidays, as some teachers took pity on my, and could perhaps see some sort of potential, as I was one of a very small number of kids who programmed rather than just played games. So buying a second-hand BBC micro in 1992 - while at university - was a dream come true. My friends couldn't understand why I wanted one, nor why I was willing to pay £100 for the privilege, but I really didn't care. Then about 2 months later, I bought a B+ in a university departmental auction for only £30, which was absolutely amazing. The brand new Master was the best of all though. Not only did I finally have the chance to have a brand-new-in-box machine, but it was only £50. I spotted the ad in the back of a computer magazine - they were being sold by Acorn Direct - and when I rang them, they guy explained that schools, etc, were snapping them up because that price was cheaper than a replacement PSU! I still remember how happy I was on the day it arrived - and how my friends (at work, this time) still didn't understand me...
This very late machine had a different keyboard to the rest. No more individual key switches this time. Perhaps just as well, as the Master keyswitches were less reliable than the earlier types IME. This one was more like a PC keyboard, and was made for Acorn by Cherry. It feels quite different to a regular BBC keyboard, but is better IMO - more like a PC keyboard, and definitely easier to type on.
One thing that amazes me: just how many of my original 5.25" discs are still working. I don't recall any bad ones really, though I'm sure there must have been a couple over the years. I haven't been overly-careful about how I treat them - obviously I try to keep them away from magnets, but they've had time in attics and other non-ideal places. I did find that I've had more EPROM failures than disc failures. Some of the failures appeared to be actual failures, rather than amnesia. I've got stacks of rescued EPROMs from other random gear, and all the images I'm ever likely to need are freely available on-line, and of course, if you have a Master (or B+ 128k*), then you don't need to burn them as you can just load them into sideways RAM.
* I did borrow the one and only 128k B+ our school had for a 6 week summer holiday once. But we couldn't find the specific user guide for it, so I didn't know how to take advantage of the extra RAM, over and above the 20k of shadow RAM. I learnt about it much later, but long after leaving school.
Happy days! I did have a go at assembly a few months back, just to see how much of it I remembered: more than I expected, but that's not saying much!
I normally have a BBC Master set up in the office, and the kids like to play an occasional game or two. I sometimes like to dig out something from the past - sometimes just for fun, sometimes for real, as it were. But I decided that I needed to pack it all away to make space for another PC. Before doing so, however, I needed to resurrect my old model B to print out a couple of diagrams that I did back in school. The software wasn't compatible with the Master.
The PSU in the model B had a label saying that the -5V rail was missing. I'd written that when I thinned down my Acorn collection, about 10 years ago. I think the PSU came from another machine, and I took the good one from this model B to help out the person taking away the chosen machines. No problem - just a case of changing a diode on the secondary side. While it was apart, I replaced the two RIFA caps on the mains side, and the electrolytic on the primary side that always causes problems. I then found problems with compatibility with my disc drives. I wondered if it was because of having version 0.9 of the DFS installed, and that prompted me to dig out my EPROM programmer, along with the Windows 98 machine needed run it - the usual sort of "rabbit hole" old computers send you down...
In parallel with that, I decided to try my B+ machine. This worked perfectly, but - you guessed it - after about 5 minutes, one of the RIFA caps let go! Ironic, given that I had just refurbished the other PSU, which hadn't yet blown its RIFAs. Still, no harm done, and refurbing the B+ PSU was obviously a good thing to do.
Trying the software, I found that although it wasn't compatible with the Master, it was OK with the B+. So time to hook up the Epson dot matrix printer, complete with new ribbon, and try to remember how to drive the software to get the print-outs. That all worked well after I found an ancient photocopy of the user instructions. Job done.
Meanwhile, I'd made a DFS 1.2 ROM for the model B, and it appeared to work as a ROM, but I was still having disc issues...
I remembered that I had another model B - a really tatty one that was missing its PSU. It had been modified to be used as a VT clock, so had a genlock card fitted - not an easy mod. I decided that perhaps now was a good time to bring this back to original spec, so I carefully removed all the mods. That was easier said that done, and there were a couple of things that took a bit of time to sort out - nothing worth relaying here as it's unlikely anyone else would run into the same problems, but it certainly took longer than it should! But once working, I took it upstairs to try in the office, and had exactly the same disc issues!
So I dug out another drive from the attic, and the problems all went away! So no need to have attacked the modified B, but at least that's behind me now. If I find another PSU - and ideally another case - then I've got another working machine. I think the problems were a compatibility issue with the newer drives in my setup upstairs (which would have been sold as drives for PCs, but can be made to work with some(!) BBC machines with the right link settings) and the earlier 8271 controller chip. The B+ and onwards used the 1770, which is definitely happy with these later drives (decent ones, made by TEAC).
So anyway, if you haven't already changed those RIFAs, I'd definitely recommend doing so.
I would be cautious about running them up on a variac though. Some switched-mode power supplies don't like that
I have a couple of Masters, but have never been inside their PSUs. I believe they also contain RIFAs though. Checking them out is on my to-do list...
One of my Masters was bought brand new. Though that was in 1996! During school, I desperately wanted a BBC micro, but there was no way we could afford one - plus all the peripherals needed. They were hugely expensive for even the well-off kids, let alone the likes of me, living in a council house. I was allowed to borrow one from school during the holidays, as some teachers took pity on my, and could perhaps see some sort of potential, as I was one of a very small number of kids who programmed rather than just played games. So buying a second-hand BBC micro in 1992 - while at university - was a dream come true. My friends couldn't understand why I wanted one, nor why I was willing to pay £100 for the privilege, but I really didn't care. Then about 2 months later, I bought a B+ in a university departmental auction for only £30, which was absolutely amazing. The brand new Master was the best of all though. Not only did I finally have the chance to have a brand-new-in-box machine, but it was only £50. I spotted the ad in the back of a computer magazine - they were being sold by Acorn Direct - and when I rang them, they guy explained that schools, etc, were snapping them up because that price was cheaper than a replacement PSU! I still remember how happy I was on the day it arrived - and how my friends (at work, this time) still didn't understand me...
This very late machine had a different keyboard to the rest. No more individual key switches this time. Perhaps just as well, as the Master keyswitches were less reliable than the earlier types IME. This one was more like a PC keyboard, and was made for Acorn by Cherry. It feels quite different to a regular BBC keyboard, but is better IMO - more like a PC keyboard, and definitely easier to type on.
One thing that amazes me: just how many of my original 5.25" discs are still working. I don't recall any bad ones really, though I'm sure there must have been a couple over the years. I haven't been overly-careful about how I treat them - obviously I try to keep them away from magnets, but they've had time in attics and other non-ideal places. I did find that I've had more EPROM failures than disc failures. Some of the failures appeared to be actual failures, rather than amnesia. I've got stacks of rescued EPROMs from other random gear, and all the images I'm ever likely to need are freely available on-line, and of course, if you have a Master (or B+ 128k*), then you don't need to burn them as you can just load them into sideways RAM.
* I did borrow the one and only 128k B+ our school had for a 6 week summer holiday once. But we couldn't find the specific user guide for it, so I didn't know how to take advantage of the extra RAM, over and above the 20k of shadow RAM. I learnt about it much later, but long after leaving school.
Happy days! I did have a go at assembly a few months back, just to see how much of it I remembered: more than I expected, but that's not saying much!
