Panasonic CT-1310M keeps blowing horizontal output transistor

[zeno]

See U tube for discharge vids.
You set is solid state. On turn off MOST of them bleed off in a few seconds.
It will not kill you, just teach respect. In fact in theory if you have an
irregular heart beat ( afibs) it may cure you ! Same thing as they do in
the hospital. ( cardioversion) I got bit at least once a week for 40 yrs and I am still here

The dangerous part of anything is where the AC comes in.

BTW I will take the weed thing with humor But I came from
South Acton, the beer side of town The pot heads came from West Acton
or Acton Center.

73 Zeno
LFOD !

[luRaichu]

Originally Posted by vol.2

The focus is meant to be changed while the TV is on.

Well mine died the instant I'd touched the knob. If that's really the case, something is very wrong.

Originally Posted by vol.2

Also, your pictures of the tube are not in any way conclusive as to it's health; a weak tube will still get bright, it just won't focus anymore at an acceptable level of brightness. Just be aware that you could be spending time and money trying to fix a set that will never look right

If you are just doing it for fun, and you're not that invested in the outcome, then great, but if you really are counting on it to look good in the end, you might want to skip this set and look for something cleaner that is obviously low hours

This is mostly a challenge project; after all this is an obscure set and is worth some effort. I got it for free anyways! and I'd also like to be more comfortable working around high-voltage electronics.

Originally Posted by Alex KL-1

Besides all the important tips said here, is good anyway to check +B to see if it is too high, starting measuring the video output supply voltage (one pin of L351), if derives from flyback. Typically it have 180V, and above 200V is considered very suspicious.

How exactly would I do this with my multimeter? also this measurement would require a new HOT. Two new HOTs should be arriving tomorrow & the new 1500pf safety capacitor arrived today.

ALSO it'd be nice to have the Sams' for this model.

[Alex KL-1]

About the measurement... yes, this one requires the system functioning. Is good to measure "in a hurry", with the + lead of the multimeter attached to the point (negative from multimeter will be to circuit ground, like the channel selector shield or some easy point), and then powering up the TV, watching as fast you can the measured voltage (before damage). Just when you are able to read the stable measurement, turn off the TV.
Then you can repeat for the HOT PSU, to take note. Same fast principle.

Is interesting both measurements, tyo see if one or both deviates from normal, to try to find soem culprit.

Another possible test, and more challenging, to check the PSU, is to remove the HOT and uses a resistor to emulate the HOT current, to independent test the PSU, before HOT eating. Some old PSU reacts bad to no load, hence the need for some load: some linear PSU rises the output voltage without load, making no-load measurement useless; and some older SMPS explodes without load.
A small lamp for emulating load... it depends, some PSU can be damaged by the filament in-rush current.

[ARC Tech-109]

With all this going on I'm wondering about the horizontal efficiency capacitors, I've had many issues with these in older JVC production monitors over the years.

[zeno]

Originally Posted by Alex KL-1

Besides all the important tips said here, is good anyway to check +B to see if it is too high, starting measuring the video output supply voltage (one pin of L351), if derives from flyback. Typically it have 180V, and above 200V is considered very suspicious.

Good call from Alex
To expand on that a cheap thing can be done. Follow the wire from L351 to the main chassis. On that line is a @4.7 mfd @350V. I can almost guarantee it
is bad & may be the problem. It can cause a lot of different symptoms
on ALL brands, its in the top ten of common fails. Also there is a SCREEN control on the CRT board. If to high it gives too bright a pix & poor focus.
Looking at the screen shots I see too bright a pix & poor focus. Too much
bright will draw too much current & stress the HOT.
Build a dim bulb tester. It will cost < $10 and will be very useful.
( socket, 2 alligator clips, some wire & a real bulb ).

enuf fer now
Zeno

[luRaichu]

Thank you for all the amazing tips. I will try to find an old lamp to cannibalize as a bulb tester gizmo.

If the +B turns out to be too high, at least we can crank it down with this variable resistor

[luRaichu]

Originally Posted by zeno

To expand on that a cheap thing can be done. Follow the wire from L351 to the main chassis. On that line is a @4.7 mfd @350V. I can almost guarantee it
is bad & may be the problem. It can cause a lot of different symptoms
on ALL brands, its in the top ten of common fails.

By this you mean a 4.7μF capacitor rated for 350V, no?

[luRaichu]

Found it. 4.7μF, lives near the HOT and is rated for 250V only. If the HOT blows again even with the brightness & screen turned down I will replace it.

[luRaichu]

This is the screen potentiometer. which side is low/high? I don't wanna risk overloading the HOT with the wrong setting. Resistance is too high to measure with my multimeter.

[luRaichu]

I resoldered the pads for the FBT, driver transformer, and the HOT leads on the main PCB. I replaced the safety capacitor & HOT. I turned screen & bright all the way down. I did NOT use a lightbulb in place of the +B fuse. I didn't measure +B either. But I did catch the HOT death on camera, sadly. https://youtu.be/3RQW40rBP8s

Here is a frame-by-frame analysis of the HOT breaking down.










I only have one HOT left. One chance to fix everything...
the +B adjustment knob is left on one extremity. so turning it the other way will either decrease +B voltage or send it through the roof.

[luRaichu]

The horizontal bands on the video were caused by me turning up the brightness. I turned it back down.

[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.