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Tech Head - The Technology Section
The Work Bench and Soldering Station
TV repair safety rules.
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<blockquote data-quote="spiney" data-source="post: 108436" data-attributes="member: 192438"><p><span style="font-family: 'Arial'">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!</span></p><p></p><p><span style="font-family: 'Arial'">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.</span></p><p></p><p><span style="font-family: 'Arial'">There are 2 big safety rules:</span></p><p></p><p><span style="font-family: 'Arial'">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).</span></p><p></p><p><span style="font-family: 'Arial'">2. Have somebody else there with you. Ideally, with some first aid knowledge and a mobile phone.</span></p><p></p><p><span style="font-family: 'Arial'">There’s 2 main “nasty areas” inside most TV sets:</span></p><p></p><p><span style="font-family: 'Arial'">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!).</span></p><p></p><p><span style="font-family: 'Arial'">2. </span><span style="font-family: 'Arial'">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.</span></p><p></p><p>(<span style="font-family: 'Arial'">also, tube neck has high dc volts some pins, maybe 400v on 2nd anode).</span></p><p></p><p><span style="font-family: 'Arial'">(The frame output stage is less dangerous, but should still be avoided).</span></p><p></p><p></p><p></p><p><span style="font-family: 'Arial'">(Plasma screen sets don’t have line or frame output stages, but moderately high dc volts may still be present on plasma panel anodes).</span></p><p></p><p><span style="font-family: 'Arial'">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).</span></p><p></p><p><span style="font-family: 'Arial'">Sorry to be “preachy”, but it really is dangerous, so please be careful!</span></p></blockquote><p></p>
[QUOTE="spiney, post: 108436, member: 192438"] [font=Arial]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![/font] [font=Arial]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.[/font] [font=Arial]There are 2 big safety rules:[/font] [font=Arial]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).[/font] [font=Arial]2. Have somebody else there with you. Ideally, with some first aid knowledge and a mobile phone.[/font] [font=Arial]There’s 2 main “nasty areas” inside most TV sets:[/font] [font=Arial]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!).[/font] [font=Arial]2. [/font][font=Arial]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.[/font] ([font=Arial]also, tube neck has high dc volts some pins, maybe 400v on 2nd anode).[/font] [font=Arial](The frame output stage is less dangerous, but should still be avoided).[/font] [font=Arial](Plasma screen sets don’t have line or frame output stages, but moderately high dc volts may still be present on plasma panel anodes).[/font] [font=Arial]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).[/font] [font=Arial]Sorry to be “preachy”, but it really is dangerous, so please be careful![/font] [/QUOTE]
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TV repair safety rules.
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