1980 Sears (Sanyo) 25" Console TV CRT Problem

[tv beta guy]

Hello everybody. I've actually been a member since when it was still all Audiokarma. Says since May of 2004. Due to school and such I haven't been active for a long time. I've been lurking on the boards for the past month, which I am quite addicted to. I recognize a few from YouTube here...


Anyhow, I have a problem... One I've never seen before. As in the title, it is a Sears console TV, with a Sanyo chassis.

Finally got around to repairing this TV. All that was wrong with it was a bad solder joint on the coil for the power relay. I fixed that 2 weekends ago.

So I went through the entire TV, redid gray-scale, focus, etc. It was beautiful. The TV looks like it had an honest 25 years or so of use on it until whomever owned it had the problem with the power relay. It was very well taken care of. I got it out of a recycling place.

Anyhow, so I also own a Sencore CR7000. I wanted to test the tube with it.

After I had the CRT neck board off, I accidentally plugged the TV back in. For some reason, the logic decided to turn the TV on with the neck board disconnected. I heard the degauss coil kick on and I just hurried up and unplugged it.

So I test it with my CR7000. Amazing, had 100% emissions still on all 3 guns!

So I go to put the TV back together. When I got several nice arcs inside the neck of the tube while sliding the CRT neck board back on. Scared me, but didn't think anything was damaged.

So I plug the TV back in, turn it on, and I hear a bunch of sizzling when I look back and see the neck of the tube lit up bright purple and orange.

I hurried up, unplugged, cussed.... and then got my CR7000 hooked back up to it.

Every time I tried to adjust the tester for cutoff, a big purple flash would happen inside the neck, and the tester would go into protection mode. The purple flashes were happening further up the neck, underneath the convergence/purity rings it appeared, or under the yoke.

So I'm thinking I just screwed tube up. I was very upset because the tube performed flawlessly and had 100% emissions still.
Went back to G1 short test, and now my blue gun is showing a G1 short. I tried clearing it with the tester, no go. I tried gently tapping on the neck of the tube with the plastic end of a screwdriver and ended up cracking it!!!!

Oh I was upset. Nothing I could have done at this point. So I evacuated the tube, and removed it from the TV.


I found another picture tube, one left, at Video Display Corp. It is a 25VFBP22, which is the same exact tube that was in there. So I just paid $90 + $30 shipping. It just came today, arrived without incident, and my CR7000 shows 100% emissions just testing it. It is supposed to be a NOS tube.


So I spent the time this evening putting the CRT back in the TV. Double and Triple checked my connections.


When I went to test it (luckily I still left my video camera recording), I was greeted with this:

http://www.youtube.com/watch?v=KuNyd...ature=youtu.be


The TV did not blow a fuse. That was me hurrying up and pulling the plug. And if you notice, it still made a loud pop 2-3 seconds after I killed the power. You can see when it popped the screen lit up.

I'm afraid to even turn this TV back on to just see what it is doing. Was it popping because the CRT is 30+ years old and having HV applied for the first time? I shut it off as soon as I heard popping.
I just hope I didn't screw this CRT up because I'll be out $120.

I've never seen this happen before.

All CRT ground connections are in place. No smells, nothing appears to be burnt.

Is there something I should know about these Sanyo TVs that if a certain component fails/shorts/opens/whatever, it will take out an entire CRT like I have witnessed with the original CRT?

I just don't want to power this back up yet without asking and completely destroy this CRT.

Like I said, it did not blow any fuses at all. This is a new one for me.


If anyone has any advice, it would be greatly appreciated.

Thanks.

[Eric H]

Here's my guess as to what happened.

When you tuned it on without the CRT plugged in it charged up the High Voltage, when you plugged the board back in it probably discharged through the grounds on the board.

At some point you cracked the CRT, maybe when removing the tester socket or when you plugged the CRT socket back in.

Plugging it in with air in the CRT allowed High Voltage to jump to the Guns and from there to the Video Board, possibly damaging it.

What I see in your video could be a Ground left off the CRT somewhere, perhaps the strap or spring across the bell of the tube, I have seen new CRT's snap and pop on first start up before.

I would disconnect the High Voltage lead from the bell of the tube and stick the end of it in a Glass Jar and put it somewhere away from the chassi or ground (and away from you), then I would turn the set on and see if it will run as far as sound and the heaters on the CRT lighting up.
If you have a High Voltage Probe you could check and see if it has High Voltage.

If it blows a fuse at this point then you know something is wrong, if it doesent you could plug the CRT back in and try it, double check all the grounds on the CRT and the chassis.

[lnx64]

It's nice to see you here, I definitely recognize you from YouTube, without a doubt.

Anyway, I don't have my good headphones, but I thought I heard a electrical buzzing before the zap, like it was building up energy.

Can it be the flyback? The picture flashed when it did that arcing sound, and that leads me to think it was accelerated, possibly by the flyback.

[Eric H]

I noticed the Digital Channel display went out right when it started arcing, was that you pulling the plug or did it shut down?

[radiotvnut]

Does this TV have a focus divider in the HV circuit? This will be a big resistor with one end connected to the HV anode lead, one lead will go to the focus connection of the CRT socket, and one lead will go to the focus control. If this focus divider shorted, it would place full 25-30KV on the focus pin of the picture tube and that could very well take out the CRT, as well as the tube socket. Also, take the CRT socket apart (if it will come apart) and make sure there is no evidence of arcing. It's also possible that the HV is running way too high, resulting in arcing and damage to the CRT. Zenith had that problem where the HV would run so high that it would arc and break the neck off the CRT. This was all due to the safety cap in the HOT collector circuit opening. Then, test the new CRT to make sure you didn't ruin it.

[tv beta guy]

Eric,

I will try what you suggested. I will try disconnecting the 2nd anode and try to run the TV.
I double checked my grounds. They really went all out with CRT grounding on this set: There is a flexible ground strap, which connects to the CRT neck board. And this TV has a metal shield with the degauss coil on it all around the tube. This metal shield has one ground wire also shared with a pin on the CRT neck board. And another ground wire which connects to the chassis ground. All of which are indeed touching the aquadag.
Nothing appears to be burnt or out of the ordinary on the CRT neck board. You are right about it building up a charge without the CRT being connected. I've just never seen this happen before.
And also, I pulled the plug after the first pop. That was me shutting the TV down. And then after 2-3 seconds the second pop occurred and you saw the screen light up.
Also, is there any chance, after removing the HV, that if there is a fault elsewhere, can it still take out the guns? That's what I am afraid of...

Brandon,

It was the HV from when the TV turns on. The smaller snaps are normal. And you should have heard the degauss coil as well. The loud pops are what scared me and immediately caused me to pull the plug.


Radiotvnut,

There is no focus divider. The focus wire just comes right off the flyback as its source, goes to the focus pot on the back of the TV, and then up to the CRT neck board as a black wire. A white wire returning from the CRT back down to the focus pot.
There is no evidence of arcing on this CRT neck board.

[tv beta guy]

I have some good news, I hooked my CR7000 tester back up to it.

The guns are still good! Nothing is shorted, and everything is reading 100%.

Now I just need to figure what was causing the loud popping/discharge on the HV.

I'm just really afraid of screwing up this CRT since I just bought it NOS.

[tv beta guy]

Ok, tried some things:

Tested continuity between aquadag and chassis/crt ground. I have about 1k ohms, which I will assume as normal. Direct contact with ground strap to ground is near 0 ohms. So we know we have good CRT ground.

I took Eric's suggestion and powered up the chassis with the second anode disconnected. The TV does still work. I get sound. The CRT heaters are working and no arcing, which is excellent. So I now know at least the CRT is ok. That was my main concern.

I'm done for the night.

Tomorrow shall I try hooking the second anode back up and giving it another try?

This is just odd... The HV popping was pretty loud, but it appeared to be all contained within the CRT, and it only did it twice. Just found it odd that it had that second or 2 delay then popping loud with the screen lighting up like it did.

I was just afraid of ruining a brand new CRT, hence I just had to delurk and ask for help.

[radiotvnut]

I would disconnect both the HV anode and the CRT neck board. Then, I would verify the correct HV and focus voltages as per the schematic. If these are OK, I'd check the other CRT voltages to make sure they are OK. It sounds like you got lucky on not ruining the new CRT; but, I wouldn't press my luck.

[tv beta guy]

Originally Posted by radiotvnut

I would disconnect both the HV anode and the CRT neck board. Then, I would verify the correct HV and focus voltages as per the schematic. If these are OK, I'd check the other CRT voltages to make sure they are OK. It sounds like you got lucky on not ruining the new CRT; but, I wouldn't press my luck.

Alrighty. Being that I am finally getting around to fixing my vintage television collection after an extended hiatus (I have like 50 vintage sets now), I just went on Ebay and got an HV probe. So I'll test that once I get it in. It is supposed to be around 29-30KV for this crt.

The stickers do not say what the focus voltage should be. I'm going to hunt around for any service manuals for this set then. Problem is I am missing the model nameplate. Hopefully I can go by chassis.

[mstaton]

Probably somewhere in the 4-5KV range for focus voltage

[radiotvnut]

The chassis number may be listed in the Sam's Photofact index.

[Username1]

I would like to know if you retested the old tube after removing it? and if its shorted, can your tester remove the shorts? is there any physical damage to the old tube?

If you can clear the short, reinstall the tube, make a new you tube video of the back when you power it up, and see whats sparking. Is it on the socket board? those things had ground wires too, is it on? is the B+ around 125 - 155? does this tv have a trippler? I don't think so, but had to ask. You know its possible you have a bad yoke now... Not really likely, but you need to look at what the sparks could have jumped to. I think its pretty strange you have a bad tube now from that unpowered discharge on an 80's sanyo.

[tv beta guy]

Originally Posted by Username1

I would like to know if you retested the old tube after removing it? and if its shorted, can your tester remove the shorts? is there any physical damage to the old tube?

If you can clear the short, reinstall the tube, make a new you tube video of the back when you power it up, and see whats sparking. Is it on the socket board? those things had ground wires too, is it on? is the B+ around 125 - 155? does this tv have a trippler? I don't think so, but had to ask. You know its possible you have a bad yoke now... Not really likely, but you need to look at what the sparks could have jumped to. I think its pretty strange you have a bad tube now from that unpowered discharge on an 80's sanyo.

The old tube ended up cracking in the neck after gently tapping on it trying to see if it affected my G1 short reading. So it is now gone to air. That tube is no more. I even busted the end off afterwards and pulled the electron gun assembly out and cannot see where it may have shorted. This is why I needed a new tube.

Just FYI, when the old tube was in there after the problem happened, the TV ran for about 10 seconds before I shut if off after seeing the neck lit up bright purple and buzzing (wondering why I wasn't getting a picture.) There were no HV arcing anywhere. Everything just started up normally other than that problem in the neck.

Now, I tested the TV with the new tube without the HV 2nd anode lead attached. Everything works just fine. Heaters light, everything else is hooked up including all grounds as I've mentioned above (I've checked it 4 times now. With 3 different CRT ground wires, they are all hooked up to their appropriate terminals. I took pictures and took notes before I even disassembled the set.) Everything functions as should be without HV hooked up at this point.


I bought an HV probe meter off Ebay, should be here next week to check the high voltage which should be around 30KV.


All that aside, the only thing I can think to do is try it again. I hurried up and pulled the plug on the first loud snap. After one to two seconds the tube discharged again making that second loud snap. It also scared me because the screen also lit up with it. But if you listen carefully, it also had a bunch of smaller, normal sounding snaps you'd hear upon starting up and shutting off the TV.


I've just never encountered this kind of problem before. If everything works without HV applied, could there be a problem internally with the second anode connection? As in this NOS CRT is defective? Everything else checks 100% on my Sencore tester. The loud snap/pop was internal to the tube, and caused it to light up as well as you may have seen. I had the yoke out after this incident and there are no burn marks or other indications of a failure. There were no burning smells or ozone either after this happened.

[Eric H]

At some point you are going to have to try it again with the Anode connected and let it run.
If everything is grounded as it should be then it may just take a bit for the tube to settle in on first fire up.
I recall this happening occasionally when a new color CRT was installed.

It is possible the CRT could be damaged internally even though the guns are fine, the shadow mask could have been dislodged in shipping.