[TinCanAlley]

Originally Posted by ARC Tech-109

Jailbars? Are you dealing with poor quality RF modulators or front end overload as I am? My reason for the composite input on my Magnavox was due to the IF board getting damaged while I was trying to deal with some similar issues caused by the poor quality signals coming from cheap RF modulators but the composite input introduced a number of new issues related to impedance matching and the raw input levels needed to get thru the video amps, I've since gone back to RF modulation which has brought me back to square-one and I believe the solution may be the use of CATV head end RF modulators that use SAW filters. As I understand they're far more robust and have a much cleaner output signal than the cheap-o's used in home equipment, I do have experience with these as our local senior care center has gone to great lengths to keep legacy analog MATV going in the building so those with older TV's can still use them. It's a memory care type facility and many of the residents can't operate the "new fangled" flatscreens and need their old rotary tuners from long ago, just doing our best to help those in need.

As it stands right now my issues are with a limited AGC range and what appears to be some type of "saturation" that is washing out the colors on all but the strongest saturations, set chassis in question is a T940 and thanks to member Damen I was able to get another good IF board. Now it's a matter of undoing all of my composite input mods and bring the set back to original.

I've ruled out external RF as it happens with a stand alone RF modulator, Laserdisc player's RF output and a number of other units I've tried. That's what has lead me to a possible tuner/IF issue. The replacement IF I got didn't work as a direct swap. It over saturated colors and contrast and no adjustment of color or tint made any change in color or hue. I think it's the detector voltage level. I need to set up my power supply to inject a voltage, read it on another test point and then adjust the pot in the IF for that. Since the image was there and stable, I'm sure the unit is aligned properly, just not the one voltage adjustment. That sets the voltage on the detector output going to the chroma and video board.

If the new IF doesn't fix the jailbars, I'm at a loss as I've replaced and tested every component that could cause the bars.