What's inside the back of a CRT TV and goes 'bang!'

No, it’s not a joke, or at least if it is, I don’t know the punchline.

My CRT television made a loud, sharp ‘SNAP’ sound and stopped working the other day - it sounded like an electric arc and I’m guessing that’s what it was. It still powers on and responds to the remote control, but instead of making pictures and sound, it makes the loud snap sound and turns off.

So, I’m aware of the basics of what a CRT is, so I know there are some high voltage components at the back of the tube there - and that it’s probably one of these bits that is causing the problem (I also know that it’s dangerous to go poking about in there, even after the power is disconnected, so I won’t be attempting any kind of repair myself)…

But I just wondered whether I might be describing a common fault that falls into a definite category of “it’s certainly busted - just throw it away” or “it could be something simple (like a popped capacitor) - it’s worth a try having it repaired”
It’ll cost me £25 for the shop just to take a look at it and although this is a very reasonable price, I’d rather not pay it out if there’s no hope of a repair.

Did any of the magic smoke escape? Because a high-voltage short will usually produce some.

It might be a fault in the cathode-ray tube itself – if it is breached, the vacuum will make a loud pop as the air rushes in. In that case you’re probably hosed.

There wasn’t any magical aroma, no. A bit of ozone maybe, but that could have been from static buildup on the front glass.

The snap sound happens every time I try to switch it on (well, I’ve only tried twice since the fault, then stopped, but it’s happened the same way each time) - so that rules out the vacuum implosion, I think.

However, my concern is that it might be some fairly simple fault - like an insulation failure, but that the resulting arc has fried some of the more delicate electronics.

Sounds like a good excuse to buy a new flatscreen.

Or a popped capacitor, like you said. :slight_smile:

Finances won’t permit that at the moment, sadly - it’s either repair this one or continue using the 11 inch portable that is in use as a temporary replacement.

I freely admit to not knowing what I’m talking about, but the phrase “flyback transformer” sounds like something my much more knowlegable dad would have said in a situation like this.

TVs aren’t economical to repair, sadly. Just buy a new or gently used CRT TV as a replacement - they’re cheap, reliable and will last you until you’re ready to upgrade.

I’ll guess the large capacitor or the transformer for the picture tube went bad. It’s more likely the transformer. I assume you haven’t been watering plants over it.

I’ve decided I’m going to put it in for exploratory surgery - it’s a little local TV repair shop of the old fashioned variety and the guy says that he’ll offset the £25 against the cost of repair if economical, or against the cost of a new or used replacement if not. Seems like a fair deal.

The Flyback transformer and High Voltage capacitor sometimes develop a layer of dust that causes an occasional arc, which discharges the capacitor and CRT with a bang. I’ve fixed this by giving everything a thorough cleaning, and then coating with Silicone glue.

I would nit recommend doing this unless you were very sure of what you were doing (which you’re not…)

You are lucky to have one of those shops these days.

How much are TVs in the UK? Because 25 pounds sounds like it is about 1/3 to 1/2 of the cost of a 20 inch LCD TV.

I’m not sure of the dimensions of my TV - I think it’s 22 inches. An entry-level replacement LCD screen of that size is about 400 pounds.

Sounds like either one of the capacitors has popped (unlikely unless somebody took it to bits and swapped it backwards) or the line output transformer (LOPT) has arced to ground.

It’s a lot more likely that the LOPT has popped. Either the plastic case that shrouds it has cracked due to heat and a spark has jumped to the nearby grounded screen/heatsink, or the LOPT has finally died of old age and shorted internally.

It shouldn’t be a great cost, if the parts are still available. If the LOPT pops, then generally the horizontal output transistor (HOT) goes too. The LOPT should be around £20-£40 and the HOT is about £2.

I guess some places might say they can’t get the parts, but they could just be pushing you into buying a new model. I work on old arcade games and I can still buy parts for the monitors in these and they’re 10-20 years old!


Really? If you can find me a 20" LCD for (does some quick currency conversions…) $100-$150 then holy crap, that’s a hell of a deal.

Damn. Gravity must be intense over there.


I probably did the conversion wrong but you can find them for around $200 to $250 if you are willing to get a brand you may not be familiar with. I did find a 20 inch CRT with a built in DVD player for $140. I bet that I will be able to find something for $150 if I try hard. This is however a slightly weird time to be buying TVs in the US. Companies are no longer allowed to put TVs without digital tuners into the supply chain but they can sell what they have got so some of the deals might reflect the desire to get rid of soon to be obsolete TVs.