Quote:
Originally Posted by TinCanAlley
The reason I ask is that of all the places I've scoped, the ringing is most visible on that circuit. I also remember last time I worked on it, just getting the scope's probe near the focus lead gave a ringing pattern. Is it possible for jailbars to come from the tripler?
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Yes. The tripler is part of the flyback circuit, which can be the source of the bars. When this journey started, I recommended shielding all of that to see if it went away. Did you ever try that?
Sometimes the bars can couple into the video just from proximity. One test I've done in the past is to make long extension leads between my flyback and the PCB and physically move the whole circuit away from the set and put it inside of a big steel can covered in thick plastic to prevent anything from shorting together. This is really the only foolproof way to eliminate proximity as a source for the bars coupling into the signal. It's dangerous though, so be very careful if you actually try it. I don't know how having an external tripler would effect the situation though. That's lots of high voltage parts to juggle, and the risk of arcing would be high
The important distinction here is that the bars can be one of two things. Either they are a function of the deflection, or they are a function of the video signal (ie they are modifying the actual video information before it gets draw by the deflection system).
The way you see the pulses on the probe is normal in a TV, and they will always be there. The problem is only when they are either coupled into the video signal, or when they are present in the deflection process during scan time. The bars will always be in the deflection during the blanking period and that is normal. Seeing those pulses on a probe is expected and doesn't tell you anything about where the bars are coming from.
Yes, it's normal that adding capacitance across the damper diode could cause a change in brightness. That was only to see if the bars went away, not a permanent fix.