Panasonic PT-47WX42 Convergence Issues

[tom66]

Re: Panasonic PT-47WX42 Convergence Issues

I thought your ICs were outtputing some deflection signal, it just wasn't right (but there -was- something there.) So you had a badly distorted image. Correct me if I'm wrong.

[ratdude747]

Re: Panasonic PT-47WX42 Convergence Issues

I thought your ICs were outtputing some deflection signal, it just wasn't right (but there -was- something there.) So you had a badly distorted image. Correct me if I'm wrong.

Here:

before any repair attempts: the green convergence controls were shot (had some but little image affect). the red/blue controls seemed to work. the image wasn't square (badly bowed)

After: image is highly bowed and out of convergence. The convergence controls do nothing; the arrow blinks on the screen to show it's getting the signal from the remote but the hash lines do not move.

I checked the resistors twice and they all were in spec, even the two supply resistors, which I replaced with same spec'd carbon film replacements thinking they were bad. Unless the old ones were wirewound and were slightly inductive (They looked like carbon film ones to me), I don't think that's the problem.

I read the other convergence resistors are fusable.

A few are ever so slightly browner than the others... not by a lot. They all measured up ok in circuit... should I have replaced them all anyway?

[tom66]

Re: Panasonic PT-47WX42 Convergence Issues

I've only ever touched one CRT RPTV... was a freebie Samsung 42 incher... and that ended up in pieces in the junk yard. So my record ain't great with them.

But from what I understand the ICs are basically power amplifiers, quite similar to audio amplifier hybrids but less requirement for low distortion and low noise.

If the image is bowing in it suggests the amplifier is clipping. And this could be caused by:
- faulty amplifier final stage transistors (unlikely; you've replaced the IC)
- excessive load (shorted deflection coil?)
- low supply rails (they seem OK)
- incorrect input signal
- poor decoupling (high ESR local bulk capacitance)

I'm more suspecting the 2nd, 4th or 5th. Unfortunately, this means you need to trace through the signal -- find out where it's going into the deflection ICs, and see where it's getting distorted.

[ratdude747]

Re: Panasonic PT-47WX42 Convergence Issues

I've only ever touched one CRT RPTV... was a freebie Samsung 42 incher... and that ended up in pieces in the junk yard. So my record ain't great with them.

But from what I understand the ICs are basically power amplifiers, quite similar to audio amplifier hybrids but less requirement for low distortion and low noise.

If the image is bowing in it suggests the amplifier is clipping. And this could be caused by:
- faulty amplifier final stage transistors (unlikely; you've replaced the IC)
- excessive load (shorted deflection coil?)
- low supply rails (they seem OK)
- incorrect input signal
- poor decoupling (high ESR local bulk capacitance)

I'm more suspecting the 2nd, 4th or 5th. Unfortunately, this means you need to trace through the signal -- find out where it's going into the deflection ICs, and see where it's getting distorted.

I'm leaning towards the resistors.

What's boggling my my mind is that before I could at least get each channel to do somehtign when I tried to adjust it. Now, nothing is adjustable... I'm trying to figure out what changed between now and then. I've chnaged chips twice, and unless Newark is shipping fakes, that eliminates them from the suspect list.

However, since the resistors were all in spec, I have a hard time think it's that.

I really have no idea. I'd think I'd at least get SOMETHING to happen when I tried to adjust it.. the fact NOTHING is happening has me confused.

I'd hate to have to cough up $10 for a #$%^ing service manual... But I'm at a loss for what to do here.

[ratdude747]

Re: Panasonic PT-47WX42 Convergence Issues

Ordered the resistors... for like $8 shipped, imho it's cheap insurance.

Also have a freebie service manual on the way.

[ratdude747]

Re: Panasonic PT-47WX42 Convergence Issues

The service manual didn;t help much although I think the resistors are a plausible place to look.

[ratdude747]

Re: Panasonic PT-47WX42 Convergence Issues

No dice on the resistors.

I rechecked that I had the wires plugged in the right sequence...

I even ran it with the wires unplugged... and there was no change!

I've run out of ideas... my only hint was the -20 showing up on the -18 rail .

Any other suggestions/advice or do I have a massive turd in my basement?

edit... the service manual says there shouldn't be 18V or 20V there... Looks like I need to remeasure things.

[tom66]

Re: Panasonic PT-47WX42 Convergence Issues

Can you send me the service manual? I will have a look at it (schematics), plus I can host it if you want.

[ratdude747]

Re: Panasonic PT-47WX42 Convergence Issues

Can you send me the service manual? I will have a look at it (schematics), plus I can host it if you want.

PM me for the SM.

---

Anyway... I think I see what is going on here, kinda:

Service spec | Measured

8.6V 8.4V (this was not related, just to verify my ground)

----------

-0.46V (CONV +18) 17V
-0.26V (CONV -18) -19V

It appears the +18 and -18 are NOT supply rails at all! After looking at the SM some more, they actually carry a sine wave (they gave scope specs).

I sampled a few other convergence test points... they were supposed to be 0.x kind of voltages, I saw things like 10V and the like...

Something is very wrong here.

The only other thing is that they said those were supposed to be tested with a color bar pattern... I tested mine with it at idle (displaying blue/green "component 1" in the corner) since I don't have an "NTSC function generator". I kinda doubt that's the cause of the bad readings...

What to do now?

[ben7]

Re: Panasonic PT-47WX42 Convergence Issues

...I will have a look at it (schematics), plus I can host it if you want.

I second that!
If you don't mind, you could host it for us

-Ben

[tom66]

Re: Panasonic PT-47WX42 Convergence Issues

Service manual:
http://www.tgohome.com/ServiceManual...&Search=Submit

You're welcome.

[ratdude747]

Re: Panasonic PT-47WX42 Convergence Issues

Thanks!

[ratdude747]

Re: Panasonic PT-47WX42 Convergence Issues

Any Ideas? I'm half stumped here (Once I get done with final exams next week, I'll have more free brain cells to devote to this).

[f67bird]

Re: Panasonic PT-47WX42 Convergence Issues

I should be able to help.
Did you save the original convergence I.C.s? If so, keep them separate from the new ics and mark them both with a permanent marker with an O for original... you may have to re install them later to get back to where you started from as a last resort.
But first, are both of the new convergence ics getting warm?
Please double check the deflection yoke wires (the 4 thicker wires that go to each yoke)from each crt, as well as the convergence wires (the 4 thinner wires that go to each yoke) from each crt to make sure that every one of them is going to the correct connector. The blue yoke wires need to go to the connector marked DY-B, the green yoke wires need to go to the connector marked DY-G, and the red yoke wires need to go to the connector marked DY-R. The blue convergence wires need to go to the connector marked CY-B the green convergence wires need to go to the connector marked CY-G, and the red convergence wires need to go to the connector marked CY-R. The wires are usually bunched together and held with twist connectors... untwist and follow each yoke and convergence wire set to the proper connector. The service manual shows the blue tube to be on the left as viewed from the back of the tv...verify this by turning the tv on and looking at the crt that puts out the blue color. The green crt or tube is always the one in the center, and in this case the red tube should be on the right as viewed from the back. Do not ever run the set without the yoke or convergence wires connected!
Please verify all of the above and recheck ALL resistors in the convergence circuit...especially the six 2 watt 2.2 ohm and three 2 watt 82 ohm resistors also the three 2 watt 120 ohm resistors.
Also make sure to recheck both of the .27 ohm resistors that you replaced also.
We'll go from there.
I know most of this seems overly simplistic, but when repairs get confusing as this one seems to be... the more basic things that you can go back and verify - the more the mist will clear.

[ratdude747]

Re: Panasonic PT-47WX42 Convergence Issues

Neither the chips nor the resistors got warm. Stone cold.

I replaced all the 2W resistors.

The .27 Ones were replaced but I accidentally got 1/2W ones(I guess, they were smaller than the 1W ones I removed) ... I swapped back on of the two with little change (Instead of -20V I saw -19V). I'd switch back the other one but I can't find the original (i saw it last night... ).

For those .27 ones, If I replace them again, should I go for carbon film or wirewound?

The tubes are marked already as well... I'm sure I have the convergence wires straight. The others I didn't touch so I don't know.

edit: the schematic says that the +18v IS the supply for the chips... so those itty bitty voltages the SM lists must not be from ground. Now what?

[ratdude747]

Re: Panasonic PT-47WX42 Convergence Issues

swapped back the other resistor, no change.

My only other guess is that the board is completely hosed... which means that I have a worthless money pit on my hands.

#$%^!!!

[tom66]

Re: Panasonic PT-47WX42 Convergence Issues

Have you been able to test the waveforms yet? It is the only way to trace the fault!

[ratdude747]

Re: Panasonic PT-47WX42 Convergence Issues

Have you been able to test the waveforms yet? It is the only way to trace the fault!

Given that my scope gave me nothing but garbage, no.

[tom66]

Re: Panasonic PT-47WX42 Convergence Issues

How did you set the trigger?

[ratdude747]

Re: Panasonic PT-47WX42 Convergence Issues

How did you set the trigger?

uhh... not sure how I did.

I'll retest at a later point when I have time. Any idea what frequency I'm looking for?