TV repair safety rules.

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#1
I’m a bit disturbed at people “poking around” inside tv sets. It’s difficult to kill yourself, but only 1 fatal mistake is needed!

Repair technicians plug the TV into an isolating transformer, which lets voltages “float”. Then, if they accidentally touch something nasty, it’s not quite as nasty (although hardly nice!). If you can possibly borrow an isolating transformer, it’s a very good idea.

There are 2 big safety rules:

1. Only touch tv set with one hand at any time, a “working hand”, keep the other hand well clear. That way, there’s never an “electrical path” between your hands (straight through your heart!). Preferably, keep the other hand in your pocket, and under no circumstances ever touch earthed metalwork (plumbing, central heating, kitchen appliances).

2. Have somebody else there with you. Ideally, with some first aid knowledge and a mobile phone.

There’s 2 main “nasty areas” inside most TV sets:

1. The switched mode power supply (unless a 12v “caravan” set, with external dc supply). This rectifies mains 240v ac to 350v dc (lethal!), and produces nasty voltage spikes from “chopping” it. Keep well clear. Most sets should have a safety cover over this, and a warning label, but some don’t (my cheap Beko, for example, unless you know what bits to look for, there’s nothing indicating which they are, on the single main board, close to everything else, very easy to touch accidentally!).

2. The line output stage. This has a large transformer. The voltage multiplier (“tripler”) is either nearby, or attached directly to the transformer, and has a thick wire coming out of it, going directly to the tv tube (final anode, 25-30 KV potential!). Huge voltages, so don’t touch anything around this area.

(also, tube neck has high dc volts some pins, maybe 400v on 2nd anode).

(The frame output stage is less dangerous, but should still be avoided).



(Plasma screen sets don’t have line or frame output stages, but moderately high dc volts may still be present on plasma panel anodes).

Even when tv set is disconnected from mains, there will still be residual charges stored in the switched mode electrolytic capacitors, and also the tube itself (when a tube gets changed, it’s first necessary to “discharge” the old one - often several times - before removing it).

Sorry to be “preachy”, but it really is dangerous, so please be careful!
 

Channel Hopper

Suffering fools, so you don't have to.
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#2
You forgot the first and second (and a few other ) rules,

1) Make sure you are knowledgeable in what you want to achieve in the repair.
2) Make sure you can get the spares if you find the TV needs it
3) Have the right tools to hand to start with, including a strong light and a toothbrush.
4) Make sure you have the TV unplugged from the mains before doing anything
5) Before checking the internal circuits, give the set a few hours to discharge all the voltage inside. Various makes have different LOPT circuits, and each one has a different discharge time
6) If you are thinking of repairing ANY TV for a friend or relative, make sure you have appropriate skills and insurance, before offering.

Ive once had the output from the LOPT through one hand and was touching a sink with the other, (probably explains a few things about my posts), a thrill I would pass on a second time.
 

Llew

cerca trova...
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#3
In the days of valve line O/P's we used to discharge the tube by drawing a spark from the final anode with a (long) screwdriver. Several times to make sure.

Not recommended with solid state or hybrid TV's.

Llew
 
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#4
Ok, Channel Hopper, I'll fully back up what you say above, yes, very good advice indeed!

But, I didn't "forget" anything. My original above post was a response to somebody who insised on randomly "poking about" inside a powered tv set, apparently without much of a clue about what's dangerous.

Yep, you certainly shouldn't take the back off unless you know exactly what you're doing. However, in "proper" servicing, sometimes various adjustments must be made, which require the set to be working (but I'm not "recommending" that!).
 
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#5
It may not be the same everywhere, but we could all avoid the danger if we were not charged £50 call out by the 'qualified' engineer only to be told that our £500 set was a write off, when a bit of investigation would find the short circuited 16pence capicitor.'O'-red
 

2cvbloke

Bulbs need shelter too...
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#6
I've never had any problems when repairing my TV (there was a bad solder connection on the Invertor that powers the screen, so resoldered it, I got it for free because of this fault, has been fine since, until recently), but I left it switched off for a day before I did to make sure it was reasonably safe to work on. It's starting to go again, but as it's now my only TV I'm not going to take it apart until it's dead again...

However, when I tried to repair a PC monitor once, I accidentally shorted a high-voltage component and blew a chunk out of my screwdriver and the part exploded sending a peice flying into my face, luckily it hit my cheek and not my eyes... :eek:
That was one nice monitor ruined, turned out that the power switch was broken...:(
 
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