Panasonic CT-1310M keeps blowing horizontal output transistor

[luRaichu]

I installed another HOT. When I removed the old one which blew last night, there was goopy electrical tape around the transistor base. Maybe there was an arc.


This time around I tested +B. the TV had it set to 133VDC but turning the adjustment knob all the way to the right will bring it up to 140V. I tested by setting the multimeter to 500VDC range and putting one lead on ground and the other lead on the +B fuse.

[luRaichu]

I should really replace the 4.7μF cap before doing anything else, no?
Could low +B voltage be causing a problem? You said it should be around 180VDC.

...yeah, I think a total recap is the way to go

[luRaichu]

Should I drop the lightbulb in place of the line fuse, or the +B fuse?

[damen]

There is quite a pulse on that transistor case, you can't use layers of tape to replace the original mica insulator.

[luRaichu]

Originally Posted by damen

There is quite a pulse on that transistor case, you can't use layers of tape to replace the original mica insulator.

This is 3M Super 8 electrical tape. The HOT is rated for 600v max, so is the electrical tape iirc. Although it would explain the goopified tape around one of the HOT legs.
I don't have the original mica sheet. It was glued to the old, busted HOT with some weird white substance.

[Alex KL-1]

Originally Posted by luRaichu

Should I drop the lightbulb in place of the line fuse, or the +B fuse?

Being the supply in the vicinity of 120-140V, a 120V bulb will survive of and you can protect the PSU using it in the place of +B fuse, if have one. You can test the PSU even if HOT shortens out (if is a < 30W bulb).

For the entire TV, is good to use a higher wattage one.

Test only after aplying the correct insulator (mica) and thermal grease (+1 for correcting this first).

[ARC Tech-109]

That weird white substance is the silicone heat conducting grease and without it the transistor could fail from overheating. Same stuff used on processor heat sinks and should always be used. The tape itself is not very heat conducting and its breakdown of 600V is the MAX at its nominal thickness not compressed under a transistor. There can be upwards of 1000V between the transistor case and ground during the flyback period and this is why it is so important to do things the right way, HOT's are not cheap as I remember and so far I've seen about half a dozen blown in this thread.

[luRaichu]

Originally Posted by ARC Tech-109

That weird white substance is the silicone heat conducting grease and without it the transistor could fail from overheating. Same stuff used on processor heat sinks and should always be used. The tape itself is not very heat conducting and its breakdown of 600V is the MAX at its nominal thickness not compressed under a transistor. There can be upwards of 1000V between the transistor case and ground during the flyback period and this is why it is so important to do things the right way, HOT's are not cheap as I remember and so far I've seen about half a dozen blown in this thread.

I'll have to correct you on that, I've blown a quarter dozen. They're $6 a pop, I can afford it...
But yeah this makes me feel pretty stupid. I guess I will try mounting the HOT externally just as a test to see if the previous mounting setup was bad.

[zeno]

What were the ORIGINAL HOT part numbers ?

The tape has to go ! Lets double check the ##'s then
clean it up spotless & get a mica insulator & compound.
On the U tubes I saw no reason for the fail looked
pretty normal.

Zeno

[luRaichu]

Originally Posted by zeno

What were the ORIGINAL HOT part numbers ?

The tape has to go ! Lets double check the ##'s then
clean it up spotless & get a mica insulator & compound.
On the U tubes I saw no reason for the fail looked
pretty normal.

Zeno

The original HOT was Matsushita 2SD517. I got the EXACT same replacements from eBay https://www.ebay.com/itm/294368705463

[luRaichu]

I'm going to buy these two things on Amazon.

Mica insulator -> https://www.amazon.com/gp/product/B07P428VZ1
Thermal grease -> https://www.amazon.com/gp/product/B005VULWLA

[ARC Tech-109]

The breakdown of the insulator to ground is going to kill the transistor. If I remember the heatsink was a ground potential on those Color Pilot sets, worked on may of them as they popular computer monitors in the 80s on the Apple-II that had a composite out.

[luRaichu]

How much thermal grease should be used? It should be applied to both sides of the mica, right?

[ARC Tech-109]

Yes, just a little dab is all that's needed on both sides then tighten the screws evenly allowing the thermal grease to squish out, this takes the air pockets with it.

[Alex KL-1]

Just to be on the safe side, is good to check or sub the pulse H cap (or resonating/efficiency cap). Is one generally having one pin to collector of HOT and another to ground (like the ceramic cap), in the board. It have values in the vicinity of 6 to 12nF, with at least 1600V of WV. A failure with that, and the HOT shortens out.