Panasonic CT-1310M keeps blowing horizontal output transistor

[ARC Tech-109]

I remember when HOTs were over $25.00 at Ness Electronics, as for ceramics I've seen those stacked units shift over time. I'm a 20 year member of Audiokarma and there has been a debate on & off over the decades. Regardless, I'm not into spending money on transistors just to blow them out on a chance that come capacitor is somehow going to behave, I grew up in a TV shop during the late 70's and early 80's and have seen plenty of magic smoke.

[zeno]

1) THOROUGHLY clean up tape mess
2) replace HOT & mica, compound each side & tighten evenly
3) remove B+ fuse & replace with dim bulb tester.

Now run the set watching it. The pix may be a little small and / or have
hum bars. Turn off & feel HOT every 5 mn for heat. Should be just warm.
Over current will brighten the bulb & lower HOT current. If that happens look
for a symptom, burning etc. If it runs an hour or 2 its probably OK.

This is old school BUT I remember going to a GE seminar @1975 & they
taught it for the same problem on the new SS sets, blows HOT instantly.

Zeno

[luRaichu]

Originally Posted by zeno

1) THOROUGHLY clean up tape mess

Did that, plus I recapped the TV yesterday. While recapping I found both 4.7uf caps had leaked. The one in the HOT circuit leaked so bad, one of the legs had disintegrated. I'm 99.9% sure THIS bad cap was the reason the HOT kept blowing!!


After the recap. Unfortunately as it turns out a few of these are actually bipolar, so I couldn't replace them as I didn't order any bipolar caps. Should I be worried about them?
They're marked "BP" in the image

I also got the mica insulators today but I still don't really have proper hardware for a bulb tester. Is it necessary?

[Alex KL-1]

Excellent!

About the bulb jig... is to be at safe side, due to incertainty about the flyback and PSU, to save potential HOT.

Is really possible to one of these subbed parts or the mica/tape being the culprit, but since is impossible in practice to test a flyback with DMM's, is important to consider the possibility.

Some wires, a bulb and it's socket is all needed.

Anyway, if you are very curious and wants to see it working ASAP:

Make sure to measure the PSU (the +B for HOT) at switch on with DMM already connected, to see if PSU is throwing too much voltage and promptly turning off the TV if is the case. IF the flyback is the culprit, the HOT will shorts again (so, some spare HOT is needed for this).

Late note: in fact, these bulbs are saved a lot of HOT and other parts for technicians using it, including myself.

[luRaichu]

Originally Posted by Alex KL-1

Excellent!

About the bulb jig... is to be at safe side, due to incertainty about the flyback and PSU, to save potential HOT.

Is really possible to one of these subbed parts or the mica/tape being the culprit, but since is impossible in practice to test a flyback with DMM's, is important to consider the possibility.

Some wires, a bulb and it's socket is all needed.

Anyway, if you are very curious and wants to see it working ASAP:

Make sure to measure the PSU (the +B for HOT) at switch on with DMM already connected, to see if PSU is throwing too much voltage and promptly turning off the TV if is the case. IF the flyback is the culprit, the HOT will shorts again (so, some spare HOT is needed for this).

Late note: in fact, these bulbs are saved a lot of HOT and other parts for technicians using it, including myself.

I already measured +B. it sits around 133V at the lowest setting but you can crank it up to 140V

[luRaichu]

New HOT, new caps, new mica insulator... and the H lock is totally out of whack. aaand I somehow blew the HOT again. Video tomorrow.

[Alex KL-1]

Originally Posted by luRaichu

I already measured +B. it sits around 133V at the lowest setting but you can crank it up to 140V

Is good to find the service manual or schematic with voltages, to be sure. For some TV's, 133V is fine, for others, is a lot (some works with "only" 90V; and I have one with 190V!).

[Alex KL-1]

Originally Posted by luRaichu

New HOT, new caps, new mica insulator... and the H lock is totally out of whack. aaand I somehow blew the HOT again. Video tomorrow.

Is good to check the oscillator zone. If it generates too distorted pulse (too different from the correct waveform), also have a chance to eat some HOT.

[luRaichu]

Here is a video showing the lightbulb test and hsync garbage. https://youtu.be/8A4rwF6vGKM
Perhaps I might've broke something in the +B circuit/Horizontal circuit by running with too big of a bulb, though.
edit: Towards the end of the video, you can see the HOT disconnect. Slapping the set on the side gets it back on.

Originally Posted by Alex KL-1

Is good to check the oscillator zone. If it generates too distorted pulse (too different from the correct waveform), also have a chance to eat some HOT.

I don't have an oscilloscope.

[ARC Tech-109]

Slapping the set screams of bad solder connection, a very common problem with these.

[luRaichu]

Originally Posted by ARC Tech-109

Slapping the set screams of bad solder connection, a very common problem with these.

Yeah, but I don't see any bad joints on the board. What could be the culprit?

[zeno]

HVSD a.k.a High voltage shut down.
On most sets if it activates the set goes dead. On Panny, RCA Hitachi &
some others of this era too much HV causes the H osc to go off freq.
to reduce HV. Your set is probably like that.
133 volts may be OK but you need to see if it changes. Use a variac
or go from zero brightness to full brite. It must stay the same.
Cause I have seen was always the power supply. Also the B+ control
has to go lower @125 V to put the 130VDC in range.
A manual IS needed now.

Zeno

[luRaichu]

I guess it's important to mention the +B measurement was taken before the recap. It may be different with fresh caps.

Originally Posted by zeno

Also the B+ control
has to go lower @125 V to put the 130VDC in range.
A manual IS needed now.

What do you mean? Last time I checked +B the lowest it could go with the adjustment pot was 130V. Max was 140V. But like I said, it may be different after the recap. I sure was foolish not to recheck +B.
I've been corresponding over email with someone who has a physical copy of the Sams' for this set. I asked them to send the part that shows the normal +B voltage and the H osc circuit.

[rcaman]

Why in the he$$ are you buying transistors from Ebay. 99% are junk

[luRaichu]

Originally Posted by rcaman

Why in the he$$ are you buying transistors from Ebay. 99% are junk

<vent>First off, why in the hell are you too big of a pussy to say "hell" without censoring it? Sorry for encroaching on your Christian beliefs</vent>
Secondly, I buy only QUALITY, ORIGINAL parts. The HOTs I bought are 100% legit, old stock!! And eBay is only a marketplace, you can't just say all parts sold there are junk. That's like saying all the produce at a supermarket is rotten. Maybe at yours it is