Panasonic CT-1310M keeps blowing horizontal output transistor

[luRaichu]

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.

[zeno]

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
LFOD !

[damen]

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.

[luRaichu]

Originally Posted by damen

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

[luRaichu]

Originally Posted by zeno

Almost always its the FBT. Got a variac ?

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...

Originally Posted by zeno

Also look behind the HOT for a little disc cap that likes to burn.

Yeah it's this thing right here, the safety capacitor

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.

[zeno]

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

[vol.2]

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

[luRaichu]

Originally Posted by vol.2

it's in pretty rough shape by the looks of it. unfortunately, the commercial versions rarely have a sam's,

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.

Originally Posted by vol.2

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

From what I've seen while the HOT was alive the picture tube is still good.

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.

Here it is also with the 75Ω resistance on the composite signal but with ColorPilot on.

Originally Posted by vol.2

but you might be able to find a consumer equivalent that has a fairly similar PCB in it.

There's likely a consumer set that uses the exact same PCB since mine has empty traces where tuning circuits would go.

[damen]

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.

[luRaichu]

Originally Posted by zeno

Diode looks like damper. 99% of time they dead short.

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.

Originally Posted by zeno

You can also put a regular 75 watt bulb in place of the fuse.

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)!

[luRaichu]

Originally Posted by damen

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.

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.

[damen]

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.

[luRaichu]

Originally Posted by damen

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.

[vol.2]

Originally Posted by luRaichu

I got my set to run fine for a few minutes until I killed the HOT by changing focus while the TV was on.

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

[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.