[mythtv-users] My TV doesnt like input from computers

[Chris]

> Thanks for the reply - I have only just been in a position to give
> this a try (2 months later...).
> 
> And... no go. Turning the brightness right down does nothing. It is identical.
> 
> Does anyone else have any ideas?
> 
> On 4/11/06, Marco Nelissen <marcone at xs4all.nl> wrote:
>> >I have a bit of a weird problem with my TV. When it takes input from a
>> >computer, the image is never quite right. It seems (for lack of better
>> >words to describe it), that the horizontal stretch is off. That is,
>> >the image pulls away from the sides of the tv (left and right), to
>> >leave a few cm (sometimes more then 5cm) of black space on either
>> >side. This gap isnt consistant either - it varies depending on the
>> >brightness of the image being shown. And if the brightness varies for
>> >the current image (say the top is bright, and the bottom is dark), the
>> >gap at the sides varies to.
>>
>> I've seen this with many CRTs, even computer monitors, or TVs with
>> non-computer images. It's certainly not something that's specific
>> to feeding a computer signal to a TV.
>> Basically, the horizontal deflection voltage isn't stable and being
>> influenced by picture brightness. It could be that the signal you're
>> providing is simply too bright for the powersupply to supply adequate
>> voltage to all its sub-circuits. Try reducing the brightness and see
>> if the problem goes away or is reduced to acceptable levels. If not,
>> your TV's power supply may need to be repaired. If you don't want to
>> spend the money on repair, you could try making the problem less
>> obvious by dialing up the image size until the gap is no longer
>> visible.

If this condition (called "blooming" in TV parlance) is visible ONLY 
when the picture is generated by the computer, the problem is very 
likely to be that you've set the horizontal refresh frequency 
incorrectly (either too high or too low) in your modeline.  The high 
voltage needed to operate the CRT is developed by the horizontal 
deflection circuits which are "tuned" to operate within a narrow band of 
frequencies.  If you are at the edge of that band, or outside it, the 
CRT's high voltage will go out of regulation causing just the effect you 
described.  It's not good for the TV's deflection circuits (may cause 
overheating) and if the CRT voltage gets too high it may cause the CRT 
to emit xrays so it's not a good idea to live with it.