Tech Tips Issue 5

8-bit Software (c) Duncan Webster January 1992 Issue 18 Jan/Feb 1992 TECH TIPS Before we get onto the business of this issue's tech tips, I would like to publish a letter I have received from Keith Dunn (4RR) in response to the last tech tips which explained how to get better sound output from the BBC. User: 4RR Name: Keith Dunn It was a very good item from E.M. Clarke on enhancing the sound from the BBC. Having started with my BBC some seven years ago, and at that stage being confined not only to the spare bedroom but also to a 9pm curfew on any sounds being emitted (due to sleeping children), I was forced to make modifications to the sound system very similar to Mr. Clarke's ... As he rightly points out, if you don't know one end of a soldering iron from the other then DON'T. My alteration was to fit a 3.5mm closed circuit jack between PL15 and the loudspeaker. This was then mounted on the left side of the computer just in front of the power supply unit. I had to drill a small hole to accommodate the socket on the left side of the computer base section, but by careful positioning it will fit between the moulded sections. This now reduces the amount of cable running to the back of the machine, and also allows easy access to the jack instead of fumbling around at the back. There is no need to use screened cable as the lengths are so short. Remove PL15 before any work starts. It is then just a matter of taking the routeing of one wire off the loudspeaker through to the break contacts (the TIP) on the new socket and a new length from the other side of the contacts (this will be open circuit when the jack is inserted) back to the loudspeaker. Finally from the other side of the loudspeaker a common wire to the common side of the socket(the SLEEVE). The closed circuit jack method automatically connects the internal loudspeaker when no plug is inserted, and disconnects it when one is. This is more useful to allow the possibility of either the internal loudspeaker being used or an external one, and in my case I plug in a set of lightweight headphones. Now I can stay on the computer until all hours playing all the loudest games and music without disturbing anyone else. ---------------------------------------------------------------------- Now onto this month's technical tips kindly supplied by Ted Clark and Johnathan Harston ... ---------------------------------------------------------------------- A small piece of worthless information is directed particularly to smokers in the following lines, particularly to those who "Roll their own". If you have not had the cover off your beeb for sometime, then now is the time to take a look under it. Ensure the power is off, remove the fixing screws, and lift the lid. Ghastly, isn't it?. If you do any small wiring jobs you will also probably find snippets of sleeving and bits of wire. Check once again to ensure power is off. Invert the micro and brush out all ash/tobacco etc. making sure no bits of wire remain near or trapped by I.C pins. I am sure that all micro's will benefit by this treatment. This rubbish obviously finds its way into the micro by way of the spaces between the keys, and several methods I have used to overcome this have not been really successful. The best way to avoid this accumulation is to stop smoking near the micro. I myself do not practice what I preach. One can understand why Companies who use computers ban smoking in computer environements. E. Clark ---------------------------------------------------------------------- In the past few months quite a few people have asked me to service different appliances and pieces of equipment,and I have noticed on several 13 Amp sockets that the grip screws on the plug have been gripping the separate supply and earth cable and NOT the outer sheath of the cable. This is not only shoddy work but dangerous, the cables being prone to breakage and thereby exposing bare wires and liable to cause electric shock. This is not something new. If you have 13A plugs in this condition, then fix them NOW. It may not give you a shock, but could give children or pets a very nasty nip or burn, and remember ... maybe kill ... it wouldn't be the first time 230volts has killed, so be warned. I have also heard of 3 Beeb Power Units failing in the past 3 months, and in each case self servicing by the owner has not effected a repair, and in one case a shock to one person unseated him rather rapidly. To service these units, power has to be applied, and from then on you risk a rather nasty belt from it. Sitch Mode power supplies are NOT easy to service, they operate differently from standard power units, and are much more dangerous to work on. The motto being "If you dont know what you are doing ... leave it alone." These tips are for your safety. E. Clark ---------------------------------------------------------------------- CONNECTING MORE THAN 2 DISC DRIVES TO A BEEB *8BS editor note* This information has been sent in by Johnathan Harston of Harston P.D. in response to a question posed a few months back regarding the possibility of connecting more than 2 physical disk drives to a BBC computer. Thanks to all members who responded - Johnathan's article seems to cover the problem in greatest detail ... ---------------------------------------------------------------------- You can have more two disk drives connected to a Beeb. You cannot get the computer to access them all by itself, you need to make a lead to switch the drive 0 select between the 3.5" drive and the 5.25" drive, as following: Computer Switch Disk drives DS0-------------*--- *------------------DS0 *-------------------DS2 DS1-------------------------------------DS1 You will need to tell the extra 5.25" drive to be physical drive 2 by setting it's drive select link. The making of the lead it a bit tricky. The switch has to be before the signals get to the disk drives. If the lead on you dual drive unit is long enough, and the extra 5.25" drive will fit underneath it, you can use the lead. You then take off the lid of the extra 5.25" drive, and work out where the lead has to got. It needs to go into the drive, then out again to go to the dual unit. You then connect a 34-way IDC card-edge connector in the correct place to plug into the extra drive. Connecting IDCs can be tricky. VERY Careful use of a bench vice is how I do it. Now it gets trickier... You need to connect a switch between this new plug and the computer end. You also need the switch to be somewhere accessible. So, connect a small one-pole two-way switch to three wires, about 18 to 24 inches long. Next, VERY carefully, using a sharp craft knife, separate wires 10 and 14 from the ribbon cable. Wire 1 is usually coloured red, but you can check the numbers on the connector on the disk drive. Carefully cut the two wires you have separated out, and connect them to the wires coming from the switch. The computer end of wire 10 goes to the centre of the switch. The disk drive end of wire 10 goes to one side of the switch, and the disk drive end of wire 14 goes to the other side of the switch. The computer side of wire 14 goes nowhere. All the other wires are left alone. The diagram below summs up the connections ... 1 ---------------- 2 N/C ---------------- 3 ---------------- 4 N/C ---------------- 5 ---------------- 6 DS3 ---------------- 7 ---------------- 8 index ---------------- 9 ---------------- *-----\ 10 DS0 --------------------------*---- \---------- DS0 11 ---------------- *----+ 12 DS1 ---------------- 13 ---------------- 14 DS2 ---------------- +------------ DS2 15 ---------------- : : 34 You should end up with a lead that looks something like ... 5.25" 3.5" 5.25" computer connecter drv2 drv0 drv1 ----------------------+-- ------------ ------ switch Now, make sure that the extra 5.25" drive is set to be physical drive 2, the 3.5" drive is physical drive 0 and the other 5.25" drive is physical drive 1. Switching the switch will select whether the computer sees the extra 5.25" drive or the 3.5" drive as drive 0 (DFS 0/2). The computer will see the other 5.25" drive as drive 1 (DFS 1/3). On my Beeb, I have two 5.25" drives, a 3.5" drive and a 3" drive. There is a switch to select between a 5.25" drive and the 3.5", and another to switch between the other 5.25" drive and the 3". There is also yet another switch that switches drive 0 and drive 1 around. This way, I can access use 3", 3.5" and 5.25" disks with DFS, HADFS or ADFS format. J. Harston. --------------------------------------------------------------------- Next Month will include an article on "piggy backing 2 DFS ROMs". However I would be grateful if the author of this article would supply me another copy ON DISC. I have the paper version and it would save a lot of typing if the disc could be supplied again ..... Thanks.