I'm not sure which one you mean. Which pin on the flyback is isolated? 162V (pin 10)?

FBT pulse goes to T501, rectified by D501, filtered by C502.
Note some of the ground symbols are different. Gotta use the right one when measuring.
MOST of the set uses one hot GND. If the set was newer it would
probably use a SMPS and that would add a GND. But with those
the chassis GND is cold.

Zeno:smoke:

To you too!

Q402 looks a bit weird. Q402, Q404, and the Video IC have all been replaced with new parts to check for any difference and none was found.

Also, the waveform on the other side of T401 looks correct. The rest of the set is not connected to Q402,404 besides the 134VDC supply, but even then only through a number of other components

All the parts in that whole section have been removed and checked for values with an LCR meter.

Ah! Okay, yes, I know about that. That's what I meant when I said the AV input. It's isolated by a optical input chip and then it uses T501 for its power I guess.

I did replace that filter cap, and I can't see any garbage in that circuit.

As far as I can tell, it's not in the video. I can inject and RGB signal into the Jungle IC and completely blank the video signal and the bars are still there

.

" Q402 looks a bit weird. " - What do you mean Gracie ?

.

The top of the square wave has an indentation and there is some flagging.

https://i.imgur.com/XdFYX2w.jpg

.

Hi So if that scope pic you posted is from the Base of Q402 then it loos like to me, and
my Squirrel companion, that there is a good bit of overshoot on the rising edge. I don't
know if'n yer schematic picture is of better clarity than what is posted, but I don't see
the same overshoot there..... But before we go there..... since we are looking at a
square wave thingie, does your scope have the test calibration post, where you
put your probe on it and then adjust the variable cap on the probe to adjust
it's LC balance so you don't have probe induced overshoot on your scope picture?

So if all that is sorted out, then you may have found your source of noise that
you are seeing on the screen..... See that decaying oscillation at the rising
edge is much higher in frequency than the horiz frequency, so that may
be making your "Jail Bars" looking stuff.....

I think, and the Squirrel Concurs, that you should poke around in that area and
see if there is a bad soder joint or something else, since you said you replaced
all that stuff over there.....

Good work, on that stuff, and finding a possible cause....

You may be able to add a very small .pf value ceramic cap
to the base of that transistor to see if you can dampen
it out a bit, and if it does, dampen it on the scope,
then see if it does it on the TV screen as well....

PS - While you are in that area, you should
check all wave forms, and check voltages
too & Please post any differences in
detail. - Thanks & Good Evening.

May the Squirrel be with you!

.

Yes, the probe is fine. It tests fine on the calibration source on the scope.


I went down that route a couple years ago (I've been working on this for awhile) and all components in that area test good and all the solder is good. I've been in there and had everything in and out multiple times, undoing and redoing the solder joints. Most components have been replaced, including the main video IC, and absolutely nothing has changed. All the scope readings are the same as they were when I started.

The only parts in that whole section I haven't replaced are T401 and the two inductors L418 and L412. I have spare parts in a donor TV set that is identical to the one I'm working on which I intended to try out, but it's in storage and I probably won't get to it for awhile.

In any case, the transformers and inductors are not likely to go bad as they are very simple components. I also tried using freeze spray on all the components in the section while scoping waveforms and I saw absolutely no movement or change from anything. The inductors were tested with a good LCR meter and read correct values, which is the best I think I can expect from an inductor.

Well, thanks for your input, and the Squirrel as well.

I hope I can figure it out, because if what you are saying is correct, I don't know how to make any difference. I can try a capacitor, but there is already a ceramic cap C425, 0.0022uf in that spot, and C405, 680pf, upstream from it on output of the horizontal signal from the video IC. I have already removed them and tested them and they are spot on.

.

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!

.

.

If all else fails, you could spread out that overshoot part of the scope pic & measure
the frequency of the oscillation & make yourself a filter to ground it out.

.

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

If that hoz drive is the source it must be coming from somewhere &
getting passed along. Its a classic ring that refreshes every line.
A few things....
If you cut open a jungle IC you see its a PKG of many IC's. Each usually
has its own GND & VCC pins.
I would also look at the blanking circuit. I have seen resistors in Sharp
& others cause this. Go up in value.
Mr squirrel give good advice, If you give him some peanuts & sunflower
i am sure he will help you further !
When I get ambition I will pull the Sams so I can see everything at once

73 Zeno :beer:
LFOD !

Thanks for the advice Zeno.

Are you saying I should look at the supply voltage to those chips, or suspect the ICs?

Just for reference, I have already tried replacing the jungle IC and the main video processor IC and neither had any effect whatsoever. I have extras of both.

I replaced the resistors in the area of the board that got burned. That entails R227, R497, R413, R414. There are several other resistors in that area, but they all checked out in value. I only replaced the stuff that was off, and they were all low by significantly more than 20%, I think there's a design flaw in the circuit probably for that area to get so hot.

R416 also got replaced as it was quite off, but it's not in the immediate area that looked burned.

Not totally sure which those would be. I guess maybe I didn't mess with the blanking circuit?

Just remembered. Toshiba & others used glue on bottom of the PCB
to hold wires & parts. It gets old & crusty & eats etch & gets conductive.
Clean any out you find on anything.

Zeno:smoke:

Thanks, the bottom is very clean though. I went over the board very carefully when I recapped stuff. It has also been completely cleaned with IPA and all of the solder has been reflowed.