Panasonic CT-1310M keeps blowing horizontal output transistor

[Alex KL-1]

Originally Posted by luRaichu

Should I replace just the power supply resistors, or ALL of them?

Normally, only the charred ones or with extremely bad original soldering due to overheating/thermal cycling. Measure some, and if all measure ok, don't need to continue. (again, is good to remove one leg to eliminate readings from circuit).

[luRaichu]

Originally Posted by vol.2

Pull and test any electrolytics in the supply. That's 802 803 804 805 in the 130 V, 502 in the 12V, and all those other small voltages, C558 C203 C307 C564 C1603 C1604

I replaced all of those except C1603 or C1604 since they were on the channel selector board. Best to do that while we're at it.

[luRaichu]

Originally Posted by Alex KL-1

Normally, only the charred ones or with extremely bad original soldering due to overheating/thermal cycling. Measure some, and if all measure ok, don't need to continue. (again, is good to remove one leg to eliminate readings from circuit).

Dude, R804 has got to go. It's clearly gone sour and is probably bringing a supply line or component up too high.
Here's my replacement parts list for the important PSU resistors: https://www.digikey.com/en/mylists/list/PTPXQHEAGB ("Notes" column contains part numbers from the schematic)
I also have cap lists. I'll share them later, although I could not find a replacement for the one bipolar 3.3µF @ 160v cap that lives in the H circuit. They just don't make bipolar caps with that kind of voltage tolerance anymore.

[vol.2]

Originally Posted by luRaichu

Dude, R804 has got to go. It's clearly gone sour and is probably bringing a supply line or component up too high.

I think he just meant in general you don't have to test every single resistor. If you test a bunch that look okay, then usually all of them in the same area and/or of the same type will be okay. The main thing to look out for is burned or otherwise darkened areas on the PCB or the resistors themselves. Usually newer resistors (post 1960s or so) don't go bad unless they burn up.

I will add to that, resistors can have corrosion on them like rusted legs that can go inside the package and ruin them, and that's not always visually obvious from the outside. Also, resistors can burn up partially and you won't be able to see it from the outside either.

Just check anything that looks weird and anything close to a heat source like a transistor mounted to a heatsink or smaller resistors that are next to larger power resistors that are meant to get hot

I could not find a replacement for the one bipolar 3.3µF @ 160v cap that lives in the H circuit. They just don't make bipolar caps with that kind of voltage tolerance anymore.

It's possible to create a bipolar cap from two polar caps. Do a google search for the way to do it

[luRaichu]

Originally Posted by vol.2

It's possible to create a bipolar cap from two polar caps.

A bipolar electrolytic capacitor can also be made by connecting two normal electrolytic capacitors in series, anode to anode or cathode to cathode.

What isn't mentioned is that doing it this way should cut the overall capacitance value in half. Some also say it decreases the volt tolerance.
I'm not taking a risk with such a hack.

Originally Posted by vol.2

Do a google search for the way to do it

I use DuckDuckGo and you should too, if you respect your privacy. Which is already dead, I guess.

[vol.2]

Originally Posted by luRaichu

What isn't mentioned is that doing it this way should cut the overall capacitance value in half. Some also say it decreases the volt tolerance.
I'm not taking a risk with such a hack.

You can over provision the voltage handling to avoid any risk, and you up the starting capacitance to reach the target bipolar value. It's also fairly common to parallel a film cap across the electrolytics in order to keep the ESR impedance low.

If you do it right, it's not risky.

Also, you can probably just use a film cap instead and be done with it. There are some places in a set that you might not want a film cap because it will cause ringing or uneven brightness, but most places it's fine

It used to be many years ago that film caps were simply not available in higher capacitances as electrolytics were, and they tended to be more expensive, so they didn't use them. Nowadays, you can get them up into normal value ranges pretty high; although the very high ones are still pretty expensive

[luRaichu]

Originally Posted by luRaichu

R804 has got to go.

Well, while replacing R804 today it turns out the in-circuit resistance reading was incorrect. It was always 12kΩ even with the paint bands falling off!! I replaced C1603 and C1604 but there's no difference in behavior. I have replacements for all the small value bipolar caps but something tells me that won't fix the H sync either.

The H lock fails began post-recap, picture was fine before it. First thing I did after the recap was run with a 100W or 200W lightbulb in the +B circuit. I removed the bulb when strange behavior occurred (no picture, audio still running). So either the lightbulb caused damage, or something is different after the recap.
Not to mention the other complications that appeared when reflowing solder joints for the PSU, H circuit and chroma zone.

Here are extra pages from the Sams'.

[luRaichu]

I replaced some small value bipolar caps, and the one near the horizontal driver transformer. Same issue. (didn't replace any resistors as I haven't found more bad ones YET) https://youtu.be/P8dgQ33JAhQ

Although it's hard to see in the video, the picture shrinks (and sides curve inwards) slightly as it warms up. So I think there's still an HV/power supply issue.

Oh, and I recapped the "channel selector" board & audio circuit (couldn't replace a few caps though). Now there is no sound, but I can still hear the amp working (so in other words it acts as if I don't have audio plugged in).

[luRaichu]

Q554 emitter is at 12v! What is triggering the H osc disable circuit?

[vol.2]

At this point, I wouldn't be surprised if there wasn't a hard-to-see break in the PCB or something. PCBs can get brittle with age, and a drop or a jostle (like from being taking out of storage and put on the side of the road) can cause little fractures

Usually the best way to stumble upon such an issue is by following voltages. if you get the right voltage at one end of a supply, and then you follow it along the trace to components, you will often find a break in the PCB by finding it not where it is supposed to be

It's kind of like doing a Sudoku and figuring out a row or box by omission

Of course it's not for sure, but it's one thing you could do if you're feeling stuck (follow all voltages from their supplies)

[vol.2]

The Hor lock issues could be the Hor Frequency adjustment. You usually put a small white box up, and then short a transistor in the Hor circuit and adjust the freq pot until it stands still or as close as you can get to it. Usually in older TVs I've never been able to dial it in perfect, it always drifts a little (in the adjustment phase, it always works fine after reconnecting the circuit)

Edit: actually, I just read your manual and apparently you don't need to short anything, there is an adjustment for HSYNC, R505 which can be tweaked without any other procedure

Limiting the TV power with a bulb can have weird effects on voltages inside the set. I know I've seen issues with not having enough juice to start the Hor oscillator, which can throw off voltages in that circuit. It was a tube TV though, so I don't know if the same thing can happen in a solid state set as I've never tried it

[vol.2]

Also, probe the 3.58MHz crystal in the Hor circuit to make sure it's outputting the correct frequency. If the crystal is pooched it will mess a whole slew of things up

[luRaichu]

Originally Posted by vol.2

Also, probe the 3.58MHz crystal in the Hor circuit to make sure it's outputting the correct frequency. If the crystal is pooched it will mess a whole slew of things up

I don't have a scope or frequency counter

As I said, there's 12v on Q554's emitter which means the H osc. disabling circuit is activated (which is what's deliberately throwing H sync off as a "safety feature"). I don't know why it's activating though. Could be excess HV??

[vol.2]

Originally Posted by luRaichu

I don't have a scope or frequency counter

As I said, there's 12v on Q554's emitter which means the H osc. disabling circuit is activated (which is what's deliberately throwing H sync off as a "safety feature"). I don't know why it's activating though. Could be excess HV??

Idk for absolute certainty, but I would suspect that using the bulb or a Variac could prevent the Hor oscillator from starting, which could in turn throw off voltages inside the set, or maybe do something weird with the "disabling circuit," especially if there's still something else wrong

There are some low cost scope options for someone on a budget that will at least give you some feedback. For around $100 you can get a little handheld battery powered one that will be high enough to capture the bandwidth of a crystal. Check out this video https://www.youtube.com/watch?v=iG0-0R9qYWU
The cheapest one only goes up to 200kHz, so I would probably avoid it.

[luRaichu]

Originally Posted by vol.2

Idk for absolute certainty, but I would suspect that using the bulb or a Variac could prevent the Hor oscillator from starting, which could in turn throw off voltages inside the set, or maybe do something weird with the "disabling circuit," especially if there's still something else wrong

Uhhh I don't test with the bulb anymore. The disabling circuit still activates without one present.
Please, pay more attention to the thread.