Quote:
Originally Posted by Username1
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Well Don't give up, that overshoot has a nice oscillation on it, to me that is an LC item
so maybe it's a LC pair that should be grounded, and is not. As mentioned earlier,
check out grounds, Find an LC Pair from the IC to that driver and be sure it's
really grounded.
If you disconnect the "1" voltage source on T401 will the signal on the base of Q402
clean up? Or disconnect the non grounded side of the secondary of T401 will the
signal at the base of Q402 clean up, or will the entire thing just not start up?
Since you removed almost all the components, you have to always keep
in mind you might have made a mistake putting stuff back, I think you
should check it all over good one more time....
Pin 59, 62, 61, & 63 on that IC have the right wave forms, & Voltage
readings? I'm not sure if a bad crystal could cause that.....
Is D401 A Zener Diode? Is it properly regulating the voltage to the
IC Chip? Looks like pin 58 Should have 7V on it....
Do you have 88V on the collector of Q402?
Did you change R411, R413? By any chance did you change it from a Carbon
to a Wire Wound, or Film type, or Visa Versa in any way?
Is that overshoot visible coming from the IC? (Pin 64)
or just at the base of the transistor?
I did not see anything, but may have missed it, what does
the notes say about the gray shaded components in the
circuit?
PS - A Long shot but while checking every last thing...
Might be good to be sure no leakage from Pri. to
Sec. of T401 you never know....
Have a Good Night!
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I haven't had time to check out all of this yet, but I have a couple of responses.
I did replaced R413. I believe it was carbon film and I replaced it for like, but the Service Manual does not call out what that specific resistor is made from and I did it a long time ago. I made the best guess I could based on what came out of it.
I replaced it because that whole area of the board overheated and got a bit burnt. A lot of the resistors in that area had to be replaced.
I think it's probably worth me looking at them all again to make sure I didn't violate any of the resistor types in the manual, but I don't think I did.
Just out of curiosity, why would it matter?
I double checked the waveform coming out of Pin 64, which goes to the base of Q402 and the "overshoot" doesn't line up with scan time. I took a reading from the heater and the guns, and the overshoot on Pin 64 takes place entirely during the blanking interval. Unless there are some harmonics somewhere else, but I don't see them anwhere (yet).
Also, the base of Q402 looks clean. It's the Pin out of the video IC that has the overshoot. Once it gets connected to the 134V source, it seems to restore the waveform.
Right now, I'm thinking that there is an issue originating from the secondary windings of the flyback. There might be some issue that isn't being damped properly
I'll look into the resistors