[wkat4242]

Nice job and write-up.

As the author says CRTs are dangerous. Even when they're off they can still carry insanely high voltages. The flyback transformer is one of the more dangerous components of them.

I'm great at electronics repair and I tend to avoid them. Luckily these days that's easy :)

If you don't know what you're doing, you shouldn't attempt it. Just get a more technical friend to do it.

If you do know what you're doing you probably wouldn't need this guide in the first place :)

[glhaynes]

I've never worked inside a CRT (but may need to soon) and am not great at electronics repair, but I'm a little surprised you describe yourself as having a lot of skill but still tend to avoid them. From my understanding, it's straightforward to reliably discharge them and make them safe to work on. Do you think it's easier to get this wrong than I've understood or do you just feel uneasy about it in general? Just curious!

[wkat4242]

It's just the risk. Most components in a modern TV are very safe to work on. Even the PSU is not that bad. CCFL backlight had voltages only in the hundreds of volts, and modern LED backlight is even lower. A CRT is totally different business. The author of the article pointed out another thing, wire insulation properties at such high voltages.

There's just a lot to consider, and extremely high voltage stuff isn't really my area. I tend to do more low voltage stuff. When things go wrong with high voltage they tend to go wrong pretty spectacularly, and can cause serious bodily harm too. I just prefer not to take the risk. I'm similarly cautious with Li-ion and Li-Po battery charging circuitry. I don't like to mess around with those and if I repair them it's purely a like-for-like repair.

Another thing is that when I started with electronics CRTs were still very common and I wasn't skilled then, as such I had a lot of respect for them and a lot of caution. As my skills grew, CRTs became obsolete so I never really got comfortable with them and the apprehensive feeling remained.

But I think I have skills with electronics yes, I repair a lot of electronics, designed some of my own and I also built and modded some radios, and came up with some of my own mods (I have a ham license too).

[rasz]

Im an EE that never worked on CRT and declined plenty of requests. I also like to think Im quite mechanically inclined, but I would _never_ go anywhere close to a split rim being serviced. There are things just not worth the risk in life, like jumping head down into unknown stream, or skating down handrails.

[bombcar]

Split rims is a good example of the kind of risks - they can be handled correctly but the temptation to skip steps is always there - but much more strongly there for people who do it a lot. If you replace them once, you can be anal about the safety (cage + chain + remote fill) because you don't need the speed.

I'd still replace the worst split rims with at least deuce rims.

[toast0]

One problem is there are a lot of adjustments that are really best made while the CRT is on. Another problem is CRT circuit boards experience a lot of heat, so repair work can be frustrating; it's hard to replace components and what not when traces have lifted.

[ddingus]

https://youtu.be/Vou2xlJkuoU

That technique helps a lot with traces being damaged.

[the_third_wave]

Ah, electronics hobbyists these days... I repaired my first TV at 16yo, it was a Nordmende B&W set with a resistor directly on the output of the flyback transformer. That resistor was broken which led to a nice corona discharge lighting up the inside of the set, looking at it was like looking at the set of a 30's Frankenstein movie. This set me up for a 'career' of repairing televisions and (later) monitors while at university where I came across all sorts of interesting light/sound/smoke effects from those 35kV flyback transformers with cascade circuits (called 'tripplers' since they were used to raise the output voltage) on large-tube sets.

I never got zapped which is a good thing since yes, that can be unpleasant and - depending on when and where it happens - dangerous. Discharge those tubes and cascades before you fiddle with them, use a screwdriver connected to a ground wire which is connected to the metal tube frame. If you want to do it 'professionally' you'll want to put a HT resistor in that wire, otherwise just zap the thing by sticking the screwdriver under the plastic cap on the high tension connector at the tube.

[lightedman]

It's not the transformer that's dangerous, it's the capacitor usually attached to it that's the problem. As transformers are passive components and do not store energy, they will not work without any power attached. The capacitor - if charged - will discharge through that transformer. NOW the transformer becomes dangerous, as usually the capacitor is at the low side for input, and your output voltage is multiplied a hell of a lot.

We do have the mantra in the styropyro discord "Do not the MOT" (Microwave Oven Transformer) but we all know it's harmless without power on it.

[amelius]

I've always wondered why modern multimeters don't have a "discharge" option.

I.e., you select the discharge mode, put the probes on a capacitor, and watch the voltage go down, while an internal current limiter makes sure that it happens at a safe rate.

[nickt]

The probes aren’t big enough. That’s why it’s often a big screwdriver and jump lead to earth.

The better option is the Fluke 80K 40.

https://www.fluke.com/en-us/product/accessories/probes/fluke...

[Dylan16807]

Not big enough in what way? A normal probe should be able to handle the distancing and the small current fine. Maybe it would lack insulation but I wouldn't use the word "big" for level of insulation.

[kens]

Typical probes are rated for 600 volts (CAT III), so you'd have insulation rated for 600 volts between your fingers and 30,000 volts, which is kind of hazardous.

Here's a recent Twitter video showing what happens when you combine a flyback transformer and faulty insulation: https://twitter.com/zh1nu/status/1673487720780529664

[Grazester]

Well that might have left a mark. Why would they try to touch it anyway? Even well insulated, I wouldn't try to touch something I didn't need to.

[Dylan16807]

When you combine a running transformer and weak insulation, and also there's no exposed metal where you intend for the current to go. So that probably comes off pretty differently.

But my use of the word "maybe" is more because of overall confusion about the word "big".

[tgsovlerkhgsel]

For lower voltages, some do ("low impedance measurement" or LoZ). Not specifically meant for discharging capacitors but should work for that too.

But this only works up to the voltage the multimeter is rated for (i.e. usually 300 or 600 V). If you wanted to make it safe to put 30 kV across the multimeter, it'd have to be designed with sufficient insulation etc. for that.

[formerly_proven]

An electrician's voltage tester (the not-fake ones) can be used for this, for off-line filter caps anyway. 30 kV, not so much.

[sneak]

Yeah, this webpage really should have a big prominent warning label at the top.

The flyback transformer can fucking kill you, and anyone who needs this webpage or is interested in the instructions (ie someone not working professionally in electronics repair and aware of such hazards) is less likely to know that.