5 ms·

Many "broken" electronics have fixes as simple as this. There are a lot of cheap kits on Ali Express to practice solder if its something you'd find interesting.

Many "broken" electronics have fixes as simple as this. There are a lot of cheap kits on Ali Express to practice solder if its something you'd find interesting. One of the benefits of YouTube is the depth of videos featuring diagnosis and fixing of obscure issues on rare hardware.

walrus01 6y ago
I have seen claims that as many as 80% of "dead" flat screen TVs are just a dead component in the AC-to-DC power supply. Assuming it's a problem where it doesn't power on at all, not some weird visual artifacting or physical damage to the screen. Sometimes as simple as just desoldering and replacing some capacitors... For anyone that's ever repaired a more complex power supply, the AC to DC units in a typical flat screen TV are usually really simple and easy to understand.
- lmm 6y ago
  An AC power supply is one of the most dangerous places for a beginner to try electronics repair - the capacitors can easily be holding a lethal charge even though the device is unplugged.
  - bartvk 6y ago
    It's good that you mention it, but it shouldn't deter anyone really interested. The power quickly dissipates (over the course of minutes), but you should short it with a resistor before working on it, of course.
    - hyperman1 6y ago
      Don't bet your life on minutes. As a 10 year old kid, I had an old (tube) TV that had been standing on a table for months. I wanted to unsolder some component out of it, and thought it should be safe by now. But as an extra safety measure, I decided to short the big capacitors with my metal screwdriver. Most were as dead as can be. One however, decided to surprise me with a big arc/flash that scared me stiff.
      - jmrm 6y ago
        I had the same experience as a child but with an old camera flash. While cutting a big capacitor I accidentally shorted both of the terminals. Since them I have a lot of respect to electricity.
      - myself248 6y ago
        Right, because a CRT TV is basically an enormous Leyden jar. You could've also imploded it and sent glass flying, too. None of that applies to LCDs, which are phenomenally safe to work on.
    - lmilcin 6y ago
      That may be true MOST of the time. The real issue is that SMPS are very complex and you are more likely to just cause more boom. Even probing the SMPS requires a lot of knowledge and you can easily stop vital signal that is critical for controlling the circuit and then stuff is flying around at high speeds.
      - bartvk 6y ago
        Not all of them. The Apple stuff, I agree with you.
  - bsder 6y ago
    > the capacitors can easily be holding a lethal charge even though the device is unplugged That used to be true when every power supply had a couple electrolytics as big as your fist. Only audio and guitar amplifiers are designed like this nowadays. At this point, I don't think I've seen a power supply in years that could really deliver even a slight jolt after turnoff--max is about 20uF of electrolytic cap nowadays. For a 20uF cap at 100V, it can deliver 4mA for only about half a second--that is probably just barely capable of doing something to your heart if applied directly. The bigger danger is you accidentally working on something still energized and you don't realize it.
    - throwaway0a5e 6y ago
      Not to mention that many power supplies include circuitry to discharge the capacitors whenever they are not in use (hence why many old devices with hard power switches would still consume electricity when plugged in). Regardless, the myth will almost certainly persist so long as making a low effort comment about safety is behavior people reward with internet virtue points.
    - lmilcin 6y ago
      That is bad advice. If in doubt, stay away. SMPS topologies can use capacitors on high voltage side rather than on low voltage side (like old linear supplies did). If you don't know what is the topology and how it failed you should not assume it is safe to put your greasy noob fingers in it.
      - bsder 6y ago
        You will note that my calculations assume that the caps are charged to the high-side voltages ... And I'm really, really struggling to come up with a switch-mode power supply topology design that has more than 100uF anywhere. I stand by my statement. The biggest problem when dealing with power supplies nowadays is getting the shit shocked out of you when they're plugged in--especially if you don't realize it.
  - bayindirh 6y ago
    In theory, the C13/C14 connection has a longer earth pin than live and neutral, and it should dissipate all the load while unplugging. That earth pin just zapped me only once in 15 years, I don't remember what brand it was, however it was a beefy (750W+) server PSU. Any acceptable quality PSU has internal bleed resistors to prevent shocks AFAICS.
    - fsh 6y ago
      The PE connection is exclusively for grounding exposed metal parts and is not allowed to carry any current during normal operation. Using it to discarge capacitors would probably trip the RCD circuit in a modern installation. What you really need is a bleeder resistor between the terminals of high-voltage capacitors.
    - walrus01 6y ago
      Though some TVs now come with a two pin IEC connector only...
      - bayindirh 6y ago
        Just asking due to curiosity: Do modern TVs need high voltage circuits unless they're plasmas? Also, are there any standards which force internal bleeding if there's no earth connection?
        elsjaako 6y ago
        I'm not sure about the other one, but: >Do modern TVs need high voltage circuits unless they're plasmas? The way a lot of power supplies work, is that they rectify the 110V/230V to a reasonably high DC value, and change that to a high frequency AC signal so it can be transformed to a lower voltage with a smaller transformer. This means there's typically some capacitors charged with sqrt(2) * line voltage during normal operation.
        bayindirh 6y ago
        > This means there's typically some capacitors charged with sqrt(2) * line voltage during normal operation. Thanks. Didn't know that.
  - crispyambulance 6y ago
    There are many dangerous activities in the world. Electronics repair on ordinary equipment is less dangerous than crossing the street. Folks just need to educate themselves on the basics of electrical safety, preferably with an experienced mentor, and then just get started with a healthy level of caution. Energy discharge from capacitors found in things like appliances and electronic instruments is very unlikely to be fatal. The way people usually get hurt from caps is from an involuntary jerking response to the jolt and the subsequent scraping of skin on sharp metal edges.
  - rasz 6y ago
    That statement would only be true if you allowed the premise of Police Tazers being a deadly weapon.
- kylegordon 6y ago
  Could even be less than that. 5 years ago my big old Plasma TV stopped displaying a picture. Took the back off, reseated all the connectors, stared at the multitude of SMD boards, put the back on, and it's been fine ever since! The daily driver, a 50" plasma, just celebrated its 12th birthday a few weeks ago :-)
- lmilcin 6y ago
  When I was kid my father used to recycle a lot of broken electronics. Most devices could be easily fixed (back then) assuming they haven't been damaged physically and assuming nobody else tried to fix them.
exmadscientist 6y ago
It's true that the fix is usually simple. It's also true that you can't usually put the case back together after you've gotten the damn thing apart and found the problem. At least, not unless you already had a case to practice on....
- corty 6y ago
  Depending on how obscure the hardware is, there often is a video on youtube that helps. At least for mobile phone and laptops I've always found something.
- VBprogrammer 6y ago
  I definitely recognise this phenomenon. It's amazing how easy it is to apply too much force or apply it in the wrong direction and suddenly you find some tiny plastic clip attempting to break the sound barrier. The next time you open the same thing it seems completely trivial.
- lmilcin 6y ago
  I think it is exactly the opposite. Usually, finding and fixing a problem in a PSU like that is much tougher. These are very well designed (I know because I own one) and they are usually well protected from simple faults. On the other hand they are built to be serviced. You can easily disassemble and reach any part in it. The biggest issue you will face is finding parts.
  - exmadscientist 6y ago
    The HP/Agilent/Keysight power supplies have service manuals and, more importantly, are designed to be serviced. Most consumer electronics do not and are not. My success rate on random consumer electronics is pretty good, firmware problems notwithstanding, but then it turns out something was glued or even ultrasonically welded or requires an alignment jig or was just designed by a madman and is impossible to reassemble. I've even been in the situation where something that I was on the design team for is busted and I know exactly what the fix is because I know that product but the assembly is one-way and so there's nothing I can do. (In this case the product required an IP rating and low cost, so ultrasonic welding it was.) It's very frustrating.

walrus01 6y ago

I have seen claims that as many as 80% of "dead" flat screen TVs are just a dead component in the AC-to-DC power supply. Assuming it's a problem where it doesn't power on at all, not some weird visual artifacting or physical damage to the screen. Sometimes as simple as just desoldering and replacing some capacitors... For anyone that's ever repaired a more complex power supply, the AC to DC units in a typical flat screen TV are usually really simple and easy to understand.

lmm 6y ago
An AC power supply is one of the most dangerous places for a beginner to try electronics repair - the capacitors can easily be holding a lethal charge even though the device is unplugged.
- bartvk 6y ago
  It's good that you mention it, but it shouldn't deter anyone really interested. The power quickly dissipates (over the course of minutes), but you should short it with a resistor before working on it, of course.
  - hyperman1 6y ago
    Don't bet your life on minutes. As a 10 year old kid, I had an old (tube) TV that had been standing on a table for months. I wanted to unsolder some component out of it, and thought it should be safe by now. But as an extra safety measure, I decided to short the big capacitors with my metal screwdriver. Most were as dead as can be. One however, decided to surprise me with a big arc/flash that scared me stiff.
    - jmrm 6y ago
      I had the same experience as a child but with an old camera flash. While cutting a big capacitor I accidentally shorted both of the terminals. Since them I have a lot of respect to electricity.
    - myself248 6y ago
      Right, because a CRT TV is basically an enormous Leyden jar. You could've also imploded it and sent glass flying, too. None of that applies to LCDs, which are phenomenally safe to work on.
  - lmilcin 6y ago
    That may be true MOST of the time. The real issue is that SMPS are very complex and you are more likely to just cause more boom. Even probing the SMPS requires a lot of knowledge and you can easily stop vital signal that is critical for controlling the circuit and then stuff is flying around at high speeds.
    - bartvk 6y ago
      Not all of them. The Apple stuff, I agree with you.
- bsder 6y ago
  > the capacitors can easily be holding a lethal charge even though the device is unplugged That used to be true when every power supply had a couple electrolytics as big as your fist. Only audio and guitar amplifiers are designed like this nowadays. At this point, I don't think I've seen a power supply in years that could really deliver even a slight jolt after turnoff--max is about 20uF of electrolytic cap nowadays. For a 20uF cap at 100V, it can deliver 4mA for only about half a second--that is probably just barely capable of doing something to your heart if applied directly. The bigger danger is you accidentally working on something still energized and you don't realize it.
  - throwaway0a5e 6y ago
    Not to mention that many power supplies include circuitry to discharge the capacitors whenever they are not in use (hence why many old devices with hard power switches would still consume electricity when plugged in). Regardless, the myth will almost certainly persist so long as making a low effort comment about safety is behavior people reward with internet virtue points.
  - lmilcin 6y ago
    That is bad advice. If in doubt, stay away. SMPS topologies can use capacitors on high voltage side rather than on low voltage side (like old linear supplies did). If you don't know what is the topology and how it failed you should not assume it is safe to put your greasy noob fingers in it.
    - bsder 6y ago
      You will note that my calculations assume that the caps are charged to the high-side voltages ... And I'm really, really struggling to come up with a switch-mode power supply topology design that has more than 100uF anywhere. I stand by my statement. The biggest problem when dealing with power supplies nowadays is getting the shit shocked out of you when they're plugged in--especially if you don't realize it.
- bayindirh 6y ago
  In theory, the C13/C14 connection has a longer earth pin than live and neutral, and it should dissipate all the load while unplugging. That earth pin just zapped me only once in 15 years, I don't remember what brand it was, however it was a beefy (750W+) server PSU. Any acceptable quality PSU has internal bleed resistors to prevent shocks AFAICS.
  - fsh 6y ago
    The PE connection is exclusively for grounding exposed metal parts and is not allowed to carry any current during normal operation. Using it to discarge capacitors would probably trip the RCD circuit in a modern installation. What you really need is a bleeder resistor between the terminals of high-voltage capacitors.
  - walrus01 6y ago
    Though some TVs now come with a two pin IEC connector only...
    - bayindirh 6y ago
      Just asking due to curiosity: Do modern TVs need high voltage circuits unless they're plasmas? Also, are there any standards which force internal bleeding if there's no earth connection?
      - elsjaako 6y ago
        I'm not sure about the other one, but: >Do modern TVs need high voltage circuits unless they're plasmas? The way a lot of power supplies work, is that they rectify the 110V/230V to a reasonably high DC value, and change that to a high frequency AC signal so it can be transformed to a lower voltage with a smaller transformer. This means there's typically some capacitors charged with sqrt(2) * line voltage during normal operation.
        bayindirh 6y ago
        > This means there's typically some capacitors charged with sqrt(2) * line voltage during normal operation. Thanks. Didn't know that.
- crispyambulance 6y ago
  There are many dangerous activities in the world. Electronics repair on ordinary equipment is less dangerous than crossing the street. Folks just need to educate themselves on the basics of electrical safety, preferably with an experienced mentor, and then just get started with a healthy level of caution. Energy discharge from capacitors found in things like appliances and electronic instruments is very unlikely to be fatal. The way people usually get hurt from caps is from an involuntary jerking response to the jolt and the subsequent scraping of skin on sharp metal edges.
- rasz 6y ago
  That statement would only be true if you allowed the premise of Police Tazers being a deadly weapon.
kylegordon 6y ago
Could even be less than that. 5 years ago my big old Plasma TV stopped displaying a picture. Took the back off, reseated all the connectors, stared at the multitude of SMD boards, put the back on, and it's been fine ever since! The daily driver, a 50" plasma, just celebrated its 12th birthday a few weeks ago :-)
lmilcin 6y ago
When I was kid my father used to recycle a lot of broken electronics. Most devices could be easily fixed (back then) assuming they haven't been damaged physically and assuming nobody else tried to fix them.

exmadscientist 6y ago

It's true that the fix is usually simple. It's also true that you can't usually put the case back together after you've gotten the damn thing apart and found the problem. At least, not unless you already had a case to practice on....

corty 6y ago
Depending on how obscure the hardware is, there often is a video on youtube that helps. At least for mobile phone and laptops I've always found something.
VBprogrammer 6y ago
I definitely recognise this phenomenon. It's amazing how easy it is to apply too much force or apply it in the wrong direction and suddenly you find some tiny plastic clip attempting to break the sound barrier. The next time you open the same thing it seems completely trivial.
lmilcin 6y ago
I think it is exactly the opposite. Usually, finding and fixing a problem in a PSU like that is much tougher. These are very well designed (I know because I own one) and they are usually well protected from simple faults. On the other hand they are built to be serviced. You can easily disassemble and reach any part in it. The biggest issue you will face is finding parts.
- exmadscientist 6y ago
  The HP/Agilent/Keysight power supplies have service manuals and, more importantly, are designed to be serviced. Most consumer electronics do not and are not. My success rate on random consumer electronics is pretty good, firmware problems notwithstanding, but then it turns out something was glued or even ultrasonically welded or requires an alignment jig or was just designed by a madman and is impossible to reassemble. I've even been in the situation where something that I was on the design team for is busted and I know exactly what the fix is because I know that product but the assembly is one-way and so there's nothing I can do. (In this case the product required an IP rating and low cost, so ultrasonic welding it was.) It's very frustrating.