Beeb Model B Question
Ben Newnham
when the Beeb displays anything that is white, it streaks across the
screen, why is this and how can it be fixed?
Richard Russell
If you're sure the TV is not at fault (have you tried it with another
TV?) it sounds like a problem with the UHF modulator in the Beeb. If
your TV has a SCART (or baseband PAL video) input, using that will
probably fix the fault, and give far better results than UHF anyway.
Note that the baseband video output from the Beeb by default has no
colour. You can enable PAL colour on that output by joining link LK39
on the PCB.
Best results will be obtained by using RGB, but that will need the
right SCART-to-6-pin-Din cable.
Richard.
http://www.rtrussell.co.uk/
To reply by email change 'news' to my forename.
Ben Newnham
I tried it on another TV in the house, same results. I think it must
have been modded then as it does output colour through the UHF modulator.
The TV i use with it (not used for watching things on, i have other TV's
for that) does have a SCART so if i can use the RGB on the beeb, that
would be better.
John Crane
Ben Newnham <newnh...@PLEASEDONOTSPAM.btinternet.com>
wrote:
> Richard Russell wrote:
>> On Jul 11, 7:20 pm, Ben Newnham wrote:
>>> I have a Model B connected to a 14 inch TV. The TV is tuned
>>> properly but when the Beeb displays anything that is white, it
>>> streaks across the screen, why is this and how can it be fixed?
>>
>> If you're sure the TV is not at fault (have you tried it with another
>> TV?) it sounds like a problem with the UHF modulator in the Beeb. If
>> your TV has a SCART (or baseband PAL video) input, using that will
>> probably fix the fault, and give far better results than UHF anyway.
>>
>> Note that the baseband video output from the Beeb by default has no
>> colour. You can enable PAL colour on that output by joining link LK39
>> on the PCB.
>>
>> Best results will be obtained by using RGB, but that will need the
>> right SCART-to-6-pin-Din cable.
>>
>> Richard.
>> http://www.rtrussell.co.uk/
>> To reply by email change 'news' to my forename.
> I tried it on another TV in the house, same results. I think it must
> have been modded then as it does output colour through the UHF modulator.
The LK 39 mod mentioned is for composite video output. Think it's a
rca / phono type plug if memory serves... Basically the Beeb had 3
video outputs.
1. UHF (TV) modulator - the most basic to plug into a TV aerial skt
2. Composite Video - B&W (mono) by default. LK39 gave colour
3. RGB - 6 Pin DIN - Gives best display
> The TV i use with it (not used for watching things on, i have other TV's
> for that) does have a SCART so if i can use the RGB on the beeb, that
> would be better.
--
John Crane, Iyonix RISC OS User
Ben Newnham
I found a BNC to phono lead
http://www.maplin.co.uk/Module.aspx?TabID=1&ModuleNo=1047&doy=12m7
Will that work?
Richard Russell
> I found a BNC to phono leadhttp://www.maplin.co.uk/Module.aspx?TabID=1&ModuleNo=1047&doy=12m7
>
> Will that work?
Probably, but you'll need to join LK39 to get colour.
RGB will give far better results, if you can find (or make) a suitable
SCART lead. As was pointed out, the Beeb's output is TTL, so the lead
needs to contain resistor networks to attenuate the RGB to about 1
Volt and the composite syncs to about 0.3 Volts pk-pk (into 75 ohms).
Ben Newnham
I did get one of them leads and put a jumper on the 2 pins mentioned and
i now get a much better picture with no streaking or fuzz at all and in
colour :-)
Aly
news:5PudnfrozonmOerV...@bt.com...
>I have a Model B connected to a 14 inch TV. The TV is tuned properly but
>when the Beeb displays anything that is white, it streaks across the
>screen, why is this and how can it be fixed?
The reason why the RF outputs on alot of the older computers doesn't display
properly is down to the way the signals are processed digitally in modern
televisions. They're not at all tolerant of drift.
The output is juuuuuust so ever so slightly off from the book standard.
So much for progress eh. :-/
CJE/NCS Sales
<URL:mailto:Spa...@argonet.co.uk> wrote:
> In article
> <5dc79bb3-301b-496f...@e53g2000hsa.googlegroups.com>,
> Richard Russell <ne...@rtrussell.co.uk> wrote:
> > Best results will be obtained by using RGB, but that will need the
> > right SCART-to-6-pin-Din cable.
>
>
> http://www.cjemicros.co.uk/micros/products/index.shtml
>
> But don't forget that the BBC output was 5V TTL rather than 1Vpp.
See http://www.cjemicros.co.uk/micros/individual/prodpages/CAB-BBCSCART.shtml
They're in stock! :-)
Andrew
--
CJE Micro's / 4D RISC OS Specialists
Tel: +44 (0)1903 523222 Fax: +44 (0)1903 523679
Email: sa...@cjemicros.co.uk Web: http://www.cjemicros.co.uk/
Snail mail: 78 Brighton Road, Worthing, BN11 2EN, England.