View Full Version : A problem I notice on many TV's
MRX37 04-27-2008, 02:44 PM Sometimes, especally if there are bright areas in the picture, a TV's picture will distort a bit. The best example of this is straight bars that end up curving a bit when the picture gets brighter.
The 25" Samsung TV I found awhile back does this. It kinda annoys me as I've been using it as a computer monitor. When a window pops up, the sides of it are curved inwards, making it look slightly trapezoidal like.
I notice many TV's that do this, so I'm wondering if it's an actual problem, or just a characteristic of the design? I know TV's aren't designed as good as computer monitors are...
zenith2134 04-27-2008, 03:35 PM The bending of vertical lines occurs when the contrast and brightness are jacked up too high, and the HV supply lags making the picture 'bloom'.... Actually I have noticed this on many sets, old or new, and if the power supply's electrolytic filters are changed out it can make a world of difference.
MRX37 04-27-2008, 04:42 PM Well, I don't have the brightness set very high on it. The factory default is actually a bit higher then what I have it set at.
Are the power supply's electrolytic filters those large caps that need to be discharged before removing them?
MRX37 04-27-2008, 05:56 PM Well, this TV is a few years old. It was made in 2001. If something's drifting out of spec, I wouldn't mind fixing it before it becomes a huge issue.
MRX37 04-28-2008, 10:46 AM Actually I have noticed this on many sets, old or new, and if the power supply's electrolytic filters are changed out it can make a world of difference.
So are these the caps that are large and hold a high voltage even after the set is unplugged?
RetroHacker 04-28-2008, 10:52 AM So are these the caps that are large and hold a high voltage even after the set is unplugged?
They hold some voltage. Not a ton, like the picture tube. Discharge them before you remove them though, just to avoid an unpleasant zap.
And yes, this is pretty normal - replacing the filters should help, but you may not be able to get rid of it entirely.
-Ian
MRX37 04-28-2008, 12:47 PM Oh I know it wouldn't be perfect. I've never seen a "perfect" TV. but this tv is "good enough" and has very vivid color, and since replacing the filter caps wouldn't do any harm...
I might just do that.
old_tv_nut 04-28-2008, 09:22 PM Don't get your hopes too high about changing caps, but try it if you want to.
Also, a terminology problem - you've been saying "brightness", but it's the "contrast" you need to back off on to reduce the beam current and reduce this problem.
Edit: or "Picture" control if that's what it has
zenith2134 04-28-2008, 09:55 PM old_tv_nut... thats true... Interestingly enough, Sony's usually have better regulation IME, and they're the ones which call contrast 'picture' . Some older Zeniths used white level/black level, which is without a doubt the more accurate name for the controls...
If I wanted to stiffen up the supply, I would increase the capacitance on the related lytics 'slightly' so as to not burn up any diodes. Say 15-20% increase or so, couldn't really hurt...
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