Hi,

I had an old Sanyo CRT TV that I still used from time to time. It developed a fault that I was pretty sure was a dry or cracked solder joint near the scart input. In my efforts to locate this, I thought it would be easier to completely remove the single PCB to examine the underside.

I marked the various leads that I needed to unplug. As I pulled off one of the leads attached to the flyback transformer. (Not the main one going to the back of the tube, but to the small board that plugs into the neck of the tube. At the moment this connector came off, I heard a hissing sound. I then realised the end of the neck of the tube had been completely shattered. Luckily, I was holding the connector with insulated pliers and I didn't feel anything. At this point, I had only removed one other connector (a single pin with a brown wire going from the main PCB near the flyback to the small board at the neck of tube). I hadn't removed the main wire that plugs directly into the tube.

Thanks to Google, I now realise how stupid I was to attempt this and at the very least, I should have discharged the tube. I don't think I would ever pull the back off another CRT even if I had one. I am though very interested to learn exactly what happened electrically and why pulling that particular lead off would have instantly killed the tube. I would be very grateful to anyone who could offer an explanation.

 

I think that the neck of the tube was mechanically damaged possibly by the board on the end of the tube being pulled at an angle. Usually the 'pip' on the end of the tube goes inside the socket for the tube pins and pulling at an angle can then break the 'pip'.

 

I suspect that was nothing to do with the EHT, somehow inadvertently you placed stress on the socket end somehow and ended up evacuating the CRT.
Max.

 

Thanks for the fast replies, that's really very interesting and not what I was expecting. I was convinced the damage was caused by me pulling off that wire.

The connector in question would not have been insulated when I removed it, as I had slid the insulating boot up the wire. It was also very tight and difficult to remove even with pliers. When it finally did release in a hurry, I wonder if it could have touched something else and caused a high voltage short? What does this white wire to the flyback actually do and would a voltage have been present on the disconnected pin?

Until I heard the gas escaping, I hadn't touched the board on the end of the tube, and as far as I know, I hadn't damaged it. The break in the neck looks a bit further down than the pip you describe.

I have attached a couple of photos showing where the break is and also the white wire I disconnected.

 

Definitely appears to be external damage to the socket end, I suspect you inadvertently pulled on a socket pin.
The only dangerous point on the HV is the anode lead and also any charge still present in the internal Aquadag coating, which acts as a capacitor and stores a charge for several hours, the outer Aquadag is the other plate of the cap, but at GND .
potential.
The really dangerous evacuation of a crt is not really at the neck, it is when the front of the screen is damaged, Ask me how I know!
.Either way, its BUSTED!
Max.

 

The pins on the end of the tube look bent.

 

What gas actually escaped from where? Absolutely ignorant here.

 

I was convinced the damage was caused by me pulling off that wire.

If you heard the hissing, it was something you did to damage the CRT. It doesn't take much.

 

What gas actually escaped from where? Absolutely ignorant here.

The tube has a vacuum. The hissing was air going into the tube.

 

What gas actually escaped from where? Absolutely ignorant here.

No gas, it is a vacuum!
They Implode.
I fired a 22 pellet gun into the front of an old one, the 3/4" thick glass was found 20ft away.
Max.

 

Thanks. I feel better. The OP heard the gas escaping.

I always knew that vacuum was involved in this business. I even recall reading a novel where the victim was killed by shooting to a TV. Was it you Max?

 

I always knew that vacuum was involved in this business. I even recall reading a novel where the victim was killed by shooting to a TV. Was it you Max?

Not me this time!
When I first came to Canada I got a job as a service manager of a large TV store, we had one customer bring in his 23" TV, the ones with the large wooden cabinets.
The screen had obviously shattered. Upon examination there was a an also shattered beer bottle at the back of the set.
Obviously the football game didn't go the way he wanted.
Al.

 

we had one customer bring in his 23" TV, the ones with the large wooden cabinets.

Did he happen to mention if glass sprayed out after it imploded?

 

I wasn't at the front counter when he brought it in, I could have checked him for recent scar damage
Max.

 

@atferrari. Well done for stating the obvious! My questions made clear my ignorance specific to the workings of CRT's...…….. I'm guessing your ignorance is far more generalised.

Many thanks to the other contributors who were kind enough to help without judging.

 

My questions made clear my ignorance specific to the workings of CRT's...…….. I'm guessing your ignorance is far more generalized.

My heart triple bypass skills are a little rusty.
Max.

 

BTW, if wishing to discharge the CRT EHT, attach a jumper clip to chassis and the other end to the blade of a flat insulated screwdriver and slide the blade under the CRT HV connector, most likely see and/or hear a blue spark.
Just for safety.
Max.

 

@atferrari. Well done for stating the obvious! My questions made clear my ignorance specific to the workings of CRT's...…….. I'm guessing your ignorance is far more generalised.

Life is NOT fair, peji. Learn to develop a thicker skin.

 

Max, my last post wasn't aimed at you! And thanks for detailing how to safely discharge a CRT, but as I say, I don't think I'll be dabbling under the bonnet of one of these again. I might be a coward, but I'm sticking to things that won't kill me!