Can barely read the screen - how to brighten display? - Sinclair

This is my first post, I recently got a couple of SInclair 1000's and
ZX81's.

I must be doing something wrong...I have USA units. With a standard
RF converter and apater to convert the signal to a cable-in jack - all
known working equipment - I get a prompt, but it's very dark. In fact
I have to bring the contrast and brightness up all of the way just to
barely see the prompt.

This subject may have come up before...what's the solution? I even
tried a signal booster. Please .cc replies to billdeg at aol dot com.

Thanks.

Bill
vintagecomputer.net

Since my post I learned that I need to find me an old TV or old VCR
that can handle the old-fashioned signal. New TV's don't work
properly. Off to the flea market.

"billdeg" wrote in message
news:1184545280.241496.233310@n2g2000hse.googlegro ups.com...

>
> This subject may have come up before...what's the solution? I even
> tried a signal booster. Please .cc replies to billdeg at aol dot com.
>

The ZX81, and many computers of the generation, outputted video/RF signals
that weren't quite perfect and met the standard. The televisions of the day
had no problem as the signal was processed by analogue circuits in the
television.

Today's televisions mostly process signals digitally, such that if they fall
outside of the standard then unexpected things happen. That's not to say
that all modern televisions are so intolerant, but alot are.

It's widely documented. And can also be caused by a faulty ULA, but is
unlikely to be the cause. Find an old television or try a different one.
:-)

"billdeg" wrote in message
news:1184545280.241496.233310@n2g2000hse.googlegro ups.com...

>
> This subject may have come up before...what's the solution? I even
> tried a signal booster. Please .cc replies to billdeg at aol dot com.
>

The ZX81, and many computers of the generation, outputted video/RF signals
that weren't quite perfect and met the standard. The televisions of the day
had no problem as the signal was processed by analogue circuits in the
television.

Today's televisions mostly process signals digitally, such that if they fall
outside of the standard then unexpected things happen. That's not to say
that all modern televisions are so intolerant, but alot are.

It's widely documented. And can also be caused by a faulty ULA, but is
unlikely to be the cause. Find an old television or try a different one.
:-)

On Jul 15, 8:21 pm, billdeg wrote:
> This is my first post, I recently got a couple of SInclair 1000's and
> ZX81's.
>
> I must be doing something wrong...I have USA units. With a standard
> RF converter and apater to convert the signal to a cable-in jack - all
> known working equipment - I get a prompt, but it's very dark. In fact
> I have to bring the contrast and brightness up all of the way just to
> barely see the prompt.
>
> This subject may have come up before...what's the solution? I even
> tried a signal booster. Please .cc replies to billdeg at aol dot com.
>
> Thanks.
>
> Bill
> vintagecomputer.net

Bill Check out the forums on www.ts1000.us - There are a lot of posts
on there detailing how to diagnose / fix video signals on the TS1000

Bill H www.ts1000.us

Well the problem is modern TVs do not like the rough and ready output on
these machines. There is also an issue of frequency drift that rf outs are
prone to.

What you need is an old tv the sort with those little thumbwheels to tune in
the stations.

Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email: briang1@blueyonder.co.uk
__________________________________________________ __________________________________________________ __________


"billdeg" wrote in message
news:1184545280.241496.233310@n2g2000hse.googlegro ups.com...
> This is my first post, I recently got a couple of SInclair 1000's and
> ZX81's.
>
> I must be doing something wrong...I have USA units. With a standard
> RF converter and apater to convert the signal to a cable-in jack - all
> known working equipment - I get a prompt, but it's very dark. In fact
> I have to bring the contrast and brightness up all of the way just to
> barely see the prompt.
>
> This subject may have come up before...what's the solution? I even
> tried a signal booster. Please .cc replies to billdeg at aol dot com.
>
> Thanks.
>
> Bill
> vintagecomputer.net
>

Interstingly I discovered the same thing today after fitting a composite
output modification to my spectrum+
My TV card in my PC needs the brightness and contrast all the way up,
but my 7" LCD portable works fine.
the portable by the way is a 'SAKA' brand that I got from Maplin
Electronics. they were on special offer, at the time, but now are half
the price they were when I got mine. I would recommend it as it gives a
very clear and sharp picture with all my computers (spectrums and BBCs)

billdeg wrote:
I get a prompt, but it's very dark. In fact
> I have to bring the contrast and brightness up all of the way just to
> barely see the prompt.

--
link my boring website
http://myweb.tiscali.co.uk/alistairs...st/portal.html
and my boring FTP server
http://myweb.tiscali.co.uk/alistairs.../test/ftp.html

On Sun, 15 Jul 2007 17:21:20 -0700, billdeg wrote:

> I get a prompt, but it's very dark. In fact
>I have to bring the contrast and brightness up all of the way just to
>barely see the prompt.

I suspect this is perfectly "normal" operation for your computer.
The early issues did not produce the back porch part of the video.
None of my issue 1's do, but my issue 3 does, so only my issue 3
produces a display without having to turn up the brightness, as it
correctly has a black-level back-porch part of the signal.

The problem is that the few uS after a sync (ie. the back porch) is
used by the TV to set the black level (among other things). Sinclair
didn't have curcuitry to generate this in the earlier machines, so the
white was displayed immediately after the sync. However, TVs assume
the back-porch interval to always be black, so the whole screen is
made dark (ie. the TV assumes the white level on the ZX80/81 to be the
black level and automatically adjusts the brightness for you!)

In my homebuilt ZX80/81, I have designed a circuit to do this.
Basically, I stretch the SYNC pulse by about 5uS, and use this to gate
the video signal (ie. no white video during this stretched pulse), so
the first few uS after SYNC is always black, then the white signal is
enabled. This has produced an excellent display on my televisions
without having to adjust the brightness or contrast at all

Hava a look at my ZX80-81 conversion page. You'll see the circuit I
use there:

http://home.micros.users.btopenworld...0/zx80nmi.html

Hope this helps.

Grant.