Date   : Wed, 05 Oct 2005 11:38:06 +0000
From   : "bbc" <bbc@...>
Subject: T/shooting advice - bad UHF signal

G'Day all - need some advice. I got a Model B from eBay, hooked it up to
a TV via UHF Out.

The picture quality is very iffy. The signal seems to loose sync regularly,
and when it does hold sync, the white fades from being nice and bright to
very dull. There is no pattern to this.

I also noticed that there is a static sound coming from the speaker, and 
it definately seems to coincide with the drop in video signal quality. I'm 
aware of the modification to quell the noise form the speaker (adding a 
resistor), however, the fact that the increase in static noise and the video 
quality drop seem to occur at the same time leads me to believe there is 
more to the story. The static from the speaker continues with the UHF OUT
 to TV cable removed from the system, so I'm pretty sure it's not a bad cable
(although I did make the cable up myself)

I also tried using the composite out, and it seems rock stable (although
in monochrome - I'll add the extra link at some stage to give the chroma
to the output, but I'd prefer to use the UHF for convenience).

The machine itself seems to run fine. Starts up in VIEW rather than BASIC 
(just got to work out the order of the ROMs on the board), will run programs 
(tested with a simple A=A+1 PRINT A GOTO 10 sort of thing), colours are 
also fine (same program in mode 2 changing the colour of the text as well)
although they also degrade in brightness from time to time in concert with
the speaker static. It's a issue 4 mainboard.

Anyone offer some thoughts? Bad UHF modulator? Noisy power supply lines (I'm
yet to measure them to see their voltages)?

Cheers.

Steve.