Panasonic CT-1310M keeps blowing horizontal output transistor
 

I recently picked a Panasonic CT-1310M off the street. It's a commercial color CRT which accepts composite through a BNC jack and also has a VTR connector on the back, yippee! No listings on eBay for this model, barely any Google search results.
Once I got inside I'd noticed the 1.5A-125V fuse was blown so I replaced it, only to find it blew again when connecting mains power right after. Turns out the old HOT (Matsushita 2SD517) was blown & shorted out; I replaced it with the exact same part (new), left the TV set on with no signal (white screen) for a few minutes and the new HOT blew too. At that point I had one good HOT left since I ordered two. I replaced the HOT again but it blew once more when I tried adjusting the focus knob with the set still live.
Why does the HOT keep getting killed? I am currently waiting on a shipment of two new HOTs. Once I install another HOT I'll replace the safety capacitor for good measure and HOPEFULLY the HOT won't just blow again. Also it'd be nice to have the Sams' Photofact/Computerfact for this model as well.
https://i.ibb.co/pdNqkQ6/IMG-5986.jpg
https://i.ibb.co/SfTmSF0/IMG-5987.jpg
https://i.ibb.co/BLWRrPj/IMG-5988.jpg
https://i.ibb.co/9hzg1VH/IMG-5990.jpg
https://i.ibb.co/zVs6VmN/IMG-5991.jpg
https://i.ibb.co/mXztnrX/IMG-5992.jpg
https://i.ibb.co/TknXtvv/P3050170.jpg

Almost always its the FBT. Got a variac ? Run it up to @90 VAC while
watching the current. Normal is about 3/4 amp. if it goes higher
it will usually smoke & HOT will get hot. Obviously dont run long !
Also look behind the HOT for a little disc cap that likes to burn.

73 Zeno:smoke:
LFOD !

Check or replace any electrolytics around the horizontal driver transformer. Also, back in the day, counterfeit output transistors were sold, they looked good, but didn't last.

This is the one I bought, seems legit? https://www.ebay.com/itm/294368705463

No, I don't have a variac. Good luck finding a new FBT for this TV, and even if I did I'd probably shock myself trying to replace it...
Yeah it's this thing right here, the safety capacitor
https://i.ibb.co/2qMDBBZ/IMG-6117.jpg
and like I said I'll replace it with this https://www.digikey.com/en/products/...R63K7R/2356797 I'm keeping the diode since I can't find its datasheet so therefore no replacement.

You can also put a regular 75 watt bulb in place of the fuse.
Look up "dim bulb" on U tube.
Diode looks like damper. 99% of time they dead short.
BUT most are built in to HOT so be sure your replacements dont have a
built in one !
You may find a FBT but its a big gamble.

Zeno

it's in pretty rough shape by the looks of it. unfortunately, the commercial versions rarely have a sam's, but you might be able to find a consumer equivalent that has a fairly similar PCB in it.

any set i've worked on from that time period has always had a bunch of bad caps in it, and frequently bad transistors or even resistors in them. resistors that see a lot of heat can cook and die. anything anywhere around the deflection and power supply you should suspect and test

honestly wouldn't be worth it if you can't get the flyback, and you wanna test the strength of the tube as well

would be a real shame to spend a bunch of time and money fixing up a set just to find it has a dim tube, etc

This model does have a Sams' but I'm not paying $22 for it. https://www.samswebsite.com/en/photo.../model/CT1310M
I should ask my library if they have Sams', I doubt they do though.
From what I've seen while the HOT was alive the picture tube is still good.
https://i.ibb.co/DLzYBhk/vlcsnap-202...h04m04s624.png
Image is monochrome because I accidentally had the 75Ω switch flipped on and ColorPilot off; the colorburst must've been decimated.
Image is blurry probably because of the above + focus was set wrong.
https://i.ibb.co/1zkqRPf/IMG-6115.jpg
Here it is also with the 75Ω resistance on the composite signal but with ColorPilot on.
There's likely a consumer set that uses the exact same PCB since mine has empty traces where tuning circuits would go.

I have the Sams if you have any questions. Before you try another output transistor, resolder the driver transformer (T501) and any connections where a stake goes through the board and has a wire wrapped on it going to the output transistor. Also, resolder the flyback circuit board connections.

Yes that is the damper diode, and if it was shorted the HOT would blow instantly without giving a picture. I got my set to run fine for a few minutes until I killed the HOT by changing focus while the TV was on.
I measured the diode with the diode test mode on my multimeter. Few hundred ohms resistance in one direction if I remember correctly.

I don't have a lightbulb socket that'd make such a mod convenient. And what purpose would that serve? Fuse only blows when HOT is blown. Maybe you should smoke less weed (no offense)!

I'd be happy if you PM'd me the Sams' for this TV; these should all be on the Internet Archive anyways. Tomorrow I will check the resistors.

Would there be any danger in reflowing the solder on those components without discharging first? I don't have anything to perform a safe discharge at the moment. Maybe two old multimeter leads soldered together and wrapped in electrical tape will do, if they're rated high enough. I'd rather not get shocked.

I doubt that there's any shock danger if the set hasn't been powered on for a couple of days. After this length of time, the CRT would be the only charged item, maybe, that would only be a problem if you were to remove the high voltage connector. If it makes you feel better, any piece of wire bridged across the large electrolytics would discharge them. Zeno has a very good idea. Using a light bulb in place of the fuse would limit the current to the circuit, if the circuit is "normal", the bulb stays dim, an overload will cause it to be bright and you can remove power before another transistor is destroyed. Since the set does play for a "few" minutes, turn it off and feel if the transistor is cool or warm. After a few minutes if everything is normal, it should still feel cool. No shock danger as long as its off. Sorry, I don't have anyway to PM anything. I used to post diagrams on Videokarma, but they changed something and all it says is my images are too large.

You can mail me: luraichu2630 at gmail dot com. I felt the HOT right before it died, it was cold. I covered it with one layer of electrical tape to make touching safe even when live. e-tape is rated for up to 600v and that's the maximum voltage of the original HOT according to datasheets.

You can use imgbb to host pictures but don't count on them to keep your pics for decades. Also they like to add weird things to the end of their generated bbcode so make sure to remove it.

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

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

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.

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:banana:

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

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

73 Zeno:smoke:
LFOD !

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

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.

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.

Good call from Alex:yes:
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:smoke:

Thank you for all the amazing tips. I will try to find an old lamp to cannibalize as a bulb tester gizmo.
https://i.ibb.co/nCVFLZL/fuses.png
If the +B turns out to be too high, at least we can crank it down with this variable resistor:yippy:

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

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.
https://i.ibb.co/z6XbSvk/thatfunnycap.png

https://i.ibb.co/HdGSbdm/resist.jpg
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.

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.
https://i.ibb.co/gMxpyTK/vlcsnap-202...h03m50s905.png
https://i.ibb.co/mqYvws5/vlcsnap-202...h03m58s593.png
https://i.ibb.co/ZJNGkBX/vlcsnap-202...h04m01s755.png
https://i.ibb.co/wS4JwnZ/vlcsnap-202...h04m04s411.png
https://i.ibb.co/FwdcXN3/vlcsnap-202...h04m07s651.png
https://i.ibb.co/K561nG7/vlcsnap-202...h04m10s540.png
https://i.ibb.co/phhXPsf/vlcsnap-202...h04m13s370.png
https://i.ibb.co/WgY6qSy/vlcsnap-202...h04m16s444.png
https://i.ibb.co/k1yD9M8/vlcsnap-202...h04m19s675.png

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.

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

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.
https://i.ibb.co/ZgYkG7r/P4050045.jpg
https://i.ibb.co/SrKDgd8/melt.jpg
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.
https://i.ibb.co/RcWwQnt/b-adj.jpg

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

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

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.

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.

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

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

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.

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).

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

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.