You've got a problem with your micro and you just can't sort
it out on your own? Then write to MIKE COOK. If he can't help
then probably no one can . .
Curing annoying sound on vision
I HAVE recently bought a BBC Micro and I find that when it is
generating sound, interference is seen on the television screen
in the form of lines rolling vertically.
At the shop where I purchased it a second machine was found
to do the same.
This interference is especially visible on a red background.
The retailer told me that on ringing Acorn they were informed
that this interference does not constitute a fault.
I'm rather reluctant to believe this because two workmates who
also own BBC Micros don't seem to have this problem.
What I would like to know is whether this "sound on vision"
interference is displayed by all machines and the possible cause
of it.
This interference is seen clearly when running the "Music"
program on the demonstration tape. - S. Anwar. Coventry.
• This appears to be a fault with some combinations of computers
and TV sets.
The "Acorn cure" is to cut the power lead going into
the modulator and to insert a 10 ohm resistor into it. Then connect
a 100uF capacitor between the modulator side of the lead and the
modulator case.
This should smooth any supply ripple getting into the modulator
and help reduce the interference.
My cure is to solder some wires from the power lead directly
to IC 19. Pin 4 of this IC should be wired up to the 0 volts lead
and pin 6 to the +5 volts lead.
This reduces the impedance of the power supply as seen by the
audio amplifier, thus inducing less interference for the modulator
to pick up. In extreme cases you might have to do both.
Harnessing 8in discs
I REFER to your article in the January 1984 issue of The Micro
User concerning the Acorn DFS.
What has prompted me to write was your remarks about 8in floppy
discs being used on the BBC Micro.
Naturally Acorn were not forthcoming, but I and many others
would greatly appreciate an article on how to connect them up
as I have a beautiful pair of Memorex 8in drives complete with
PSU and I know two friends of mine who have similar drives - IBM
and Shugart - waiting to fit them.
I have been using a pair of Shugart 5.25in drives (35 track
though) since June 1983 but my filing system is becoming too large
- 1,400 discs actually in use and a further 720 8in discs awaiting
use!
I would greatly appreciate a reply or better still an informative
article in The Micro User. - Graham Sawyer, Stapleford, Notts.
• It is possible to use an 8in drive with the BBC Micro, but
a few links will have to be changed and tracks cut.
Having done this the Acorn disc filing system will not allow
you to use the full capacity of the disc.
To the rescue comes Vogan Products, The White House, 21 Grove
Road, Hazlemere, Bucks. HP15 7QY. They produce 8 DFS which is
an eprom disc filing system for 8in drives.
They say the product is compatible with the Acorn DFS and written
with Acorn's complete cooperation. The documentation describes
the modifications that need to be made.
The extra space is created by making the 8in disc look like
two drives to the software by having two directories.
I hope this helps you to cut down on your disc consumption.
An eye on the PSU
AN increasing amount of software is now becoming available in
ROM or eprom and there is only limited space in the BBC Micro
to fit them.
As the system can support up to 16 sideways ROMs several firms
are now producing add-on sideways ROM boards to allow for all
16 ROMs to be fitted at once.
I am a little concerned about whether the PSU can take the extra
load of all 16 ROMs in addition to my disc drive which is already
powered from the power outlet of the micro.
Presumably if I converted my single drive to a double drive
this would further increase the load.
A dealer told me that it should be all right, but didn't seem
to be very sure and finally said that he hadn't yet tried it himself.
Could you please let me know if 16 ROMs and dual disc drives
(modern slimline type) are likely to overload the PSU of the BBC
Micro? - Michael Love. Loughton, Essex.
• A dual disc drive alone is likely to overload the internal
power supply, as sometimes it cannot cope with surges that occur
when the drives turn on.
A symptom of overload is unexplicable disc errors or the machine
freezing up.
It is unusual for this to cause permanent damage to the machine
although obviously the machine will not work reliably.
Conversion connections
I HAVE recently upgraded my model A to B using a conversion
kit from one of your advertisers and with reference to your article
in the April issue of The Micro User.
The following points were not made in the magazine text (but
maybe in the kit instructions):
1. STROBE Q11(c)-PL9. pin 1 should be pulled up with 2k2. Connect
between IC27 p4 and Q11(c) - middle pin of the three. This is
R170. Check also continuity between Q11(c) and PL9, pin 1.
2. Track to PL9 pin 23 should go to pin 19. This line should
also be pulled with 4k7. Use the two plated through holes adjacent
IC70 pins 11/13. This is R162. The circuit on page 503 of the
User Guide shows this correctly.
3. Some printers (Microline 80, Star Gemini 10-x) object to
the 0V on p.26 of PL9. Isolate this pin under the socket, thus
maintaining buss continuity on PL9. P26 should be isolated on
both sides - it also sees 0V from IC83.
Again the User Guide correctly shows this connection not made.
The above refers to issue 2 and 3 boards only. Issue 4 and 7
should be okay.
Any articles on printing in the pipeline? - CJ. Young, Kings
Norton, Birmingham.
• Thank you for your help, it might clear up some problems if
you had one of the early computers.
The extra operations were not part of the upgrade from a model
A to a model B but rather minor fixes to the Issue 3 board. None
are strictly vital.
1: Provides a pull up resistor for those printers not having
one at the receiving end.
2: Helps stop the buzzing noise in the speaker found on some
Issue 3 boards.
3: Is for fussy printers.
Chips in spot 69
I HAVE a cassette game by Acornsoft bought for me with the best
intentions. However I have a BBC Model A partly upgraded to 32k.
Consequently it will not load, but tells me that IC 69 is missing.
Since my machine is a Model A this does not surprise me.
I also assume that whatever chip it is will normally be part
of the full upgrade.
I am not wanting a full upgrade because a printer is far too
expensive.
Therefore can you please answer the following questions:
• What IC goes into position 69?
• Is that all I need to allow me to use the Acornsoft cassette,
or and other proprietary sort?
• Who can supply me with the appropriate chip? - A. Fletcher,
Lowton, Warrington.
• In answer to your three questions, IC69 is a 6522 VIA chip,
this is all that is needed, and you can get it from Watford Electronics.
Not on the air
AS the BBC Micro transmits a strong carrier slightly less than
28.0MHz must we all buy CB radio licences or has Acorn a suppression
system to prevent illegal transmissions?
The carrier appears when almost any program is run and without
the need for VDU or any peripherals to be connected. - Martin
T. Pickering, Bedale, North Yorkshire.
• The BBC Micro produces considerably less radio frequency interference
or "hash" than most other computers. No licence is needed.
Teletext adapter
CAN you tell me whether I have to purchase the Teletext adaptor
to enable me to receive and record on cassette BBC teletext computer
programmes?
Seeing that I already have a Sony teletext set surely a much
simplified unit (and much less expensive) should do the job.
The Sony set has provision for a video recorder and I wondered
if BBC Micro video out plugged into this would improve display
quality - W.A. Slade, East Ham, London.
• My motto has always been that anything can be interfaced to
anything else.
However to modify an existing teletext decoder to interface
with your computer you would need to isolate your TV from the
mains with a large transformer.
Then you would have to tap into the RAM on your teletext by
inserting data select switches on the address lines and buffers
on the RAM output lines.
Having done this you would then need to feed it into your computer
through two VIAs interfaced to the 1Mhz bus. Finally you would
need to write the software to drive the modification.
All in all this is a major and complex project, and not worth
the effort in both time and cost.
* * *
I AM interested in the Beeb Body Building kit number four. Do
I need packs 1 and 2 to go with it - I have the BBC model B.
Also are wiring instructions for the same included. - C.C.
Kellam, Sheffield.
• Yes you do need the packs. To find out exactly how to use
them you'll need the July 1983 issue of The Micro User.
* * *
I WOULD be most grateful if you could tell me how the BBC Micro
can distinguish between ROMs and eproms in its language sockets,
as the enable lines for ROMs are positive to select and negative
to select for eproms. - W.H. Walker, Leighton Buzzard, Beds.
• You are wrong. The select line for both ROM and eprom is negative
to select.
SPOT THE REAL ISSUE 3 BOARD
FOLLOWING the letter entitled "Look, no mods!" in
the January 1984 issue of The Micro User I wonder if your super
sleuths could find out the serial numbers of the boards which
were screen printed "Issue 3" when they were really
of the "Issue 4" variety.
Such information could determine whether a DIY approach becomes
a possibility or not. - E. Atkinson, Keighley, West Yorkshire.
• There are lots of changes in the layout between an Issue 3
and Issue 4 board. Perhaps the easiest to spot is the small plastic
block - usually blue or yellow - on the very edge of the board
next to IC98.
This IC will just be an empty socket unless you have the speech
chips fitted. It is to be found on the left hand side of the board
about half way up.
If this block is missing you have an Issue 3 board. Page 64
of the April 1983 issue of The Micro User has a large photograph
of an Issue 3 board.
Issue 4 boards are considerably different around the top left
hand corner - the Econet region of the board.
