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    Ask HN: Tips for hacking a TV?

    76 points fewgrehrehre | 19 comments | 16 Oct 24 03:44 UTC | HN request time: 1.1s | source | bottom

    I've got a spare television lying around (specifically, a Samsung UN24H4500), and I thought it'd be fun to take a crack at seeing what I can do with it. The only hitch is that I've never really done any hardware hacking before, so I don't really know where to start!

    Any tips and pointers would be much appreciated, in terms of common ways to search for and exploit vulnerabilities, or the exploitation of other televisions. Alternatively, if this is an absolute fool's errand, and the whole thing is locked down tighter than Fort Knox, a firm warning that this is not a good thing to dick around with over a weekend would also be appreciated.

    1. purple-leafy ◴[16 Oct 24 05:30 UTC] No.41855906[source]▶
    Whatever you do, don’t touch the capacitors, especially if it’s an old TV, even if it’s unplugged. Could kill you. Old TV caps pack a serious punch (even when unplugged)
    replies(6): >>41862027 #>>41866933 #>>41871123 #>>41877332 #>>41877889 #>>41878329 #
    2. fewgrehrehre ◴[16 Oct 24 18:18 UTC] No.41862027[source]▶
    Thank you very much! I will keep that in mind.
    3. laserstrahl ◴[17 Oct 24 06:23 UTC] No.41866933[source]▶
    Ya, i can relate.
    replies(1): >>41877946 #
    4. squidgedcricket ◴[17 Oct 24 16:25 UTC] No.41871123[source]▶
    I think that's no longer true for modern flatscreen TVs. Older CRT TVs had caps charged to a dangerously high voltage, but all the caps on an LED/LCD TV should be a low enough voltage to be touch safe.
    replies(4): >>41874010 #>>41877054 #>>41877871 #>>41878796 #
    5. purple-leafy ◴[17 Oct 24 21:30 UTC] No.41874010[source]▶
    Touch safe, how about lick safe?
    replies(1): >>41877286 #
    6. ale42 ◴[18 Oct 24 07:18 UTC] No.41877054[source]▶
    Except for the switching power supply, where you have capacitors charged at (rectified) mains voltage so around 155 or 325 volts depending on where you are. They should discharge relatively quickly, but they might be dangerous for a few minutes.
    7. throwup238 ◴[18 Oct 24 08:03 UTC] No.41877286{3}[source]▶
    That’s what flyback transformers were for. If you licked them, you’d fly back.
    8. ta1243 ◴[18 Oct 24 08:12 UTC] No.41877332[source]▶
    The UN24H4500 is an LED monitor.

    The big risk in old TVs was the enormous voltages in the CRTs (which acted as a capacitor and stored energy even when off, and even pick up energy from background sources)

    replies(1): >>41878330 #
    9. KaiserPro ◴[18 Oct 24 10:08 UTC] No.41877871[source]▶
    Mains will still kill you, even if its not 3.3kv or what was needed to run a CRT.

    Its always best to work out where the mains PSU is, and either cover/isolate it so that you don't touch it by accident. Even if turned off, there is a non-insigificant risk that there is either mains power lying around or some other large charge/current ready to bite.

    THe back of the inlet is also tends to be a hazard, so be really careful around there too.

    replies(1): >>41877917 #
    10. hagbard_c ◴[18 Oct 24 10:11 UTC] No.41877889[source]▶
    That may have been true a long time ago in the age of CRT (picture tube) televisions but anything with a flat screen contains a bog-standard switching power supply with a bunch of 450V-or-so capacitors which will give you a nasty bite but not much more than that. In CRT sets it typically [1] wasn't the discrete capacitors which posed a problem but the CRT itself which was used as a smoothing capacitor for the HT power supply. The in- and outside of the back of the tube were (are) covered with a conducting paint (e.g. 'Aquadag' [2], a colloidal graphite coating) with the inside connected to the HT power supply and the outside connected to ground. That 'internal capacitor' can keep its charge for a long time. As to whether it 'can kill you' that seems to depend on a lot of factors ranging from the discharge path, physical condition of the subject and more. There are many reports on people getting zapped who describe it as 'a nasty jolt' but survivor bias means this is not what you should go by - just avoid getting zapped by discharging the tube.

    [1] there are exceptions, e.g. older vacuum tube sets which used a mains-driven EHT circuit with discrete capacitors

    [2] https://en.wikipedia.org/wiki/Aquadag

    11. i_am_proteus ◴[18 Oct 24 10:15 UTC] No.41877917{3}[source]▶
    Can't echo this enough. If you're working on anything that has been connected to residential mains... use a multimeter. They're cheap! Check the power supply for residual voltage from PSU caps. Discharge them safely before working on the equipment!
    replies(1): >>41878491 #
    12. dommer ◴[18 Oct 24 10:20 UTC] No.41877946[source]▶
    Me too. I was about 8 when I took my TV apart and brushed my arm against that capacitor. Packed a wallop, and kept my arm in a ridged state for a bit.
    13. HumanOstrich ◴[18 Oct 24 11:20 UTC] No.41878329[source]▶
    TVs that old didn't need to be hacked.
    14. BoxOfRain ◴[18 Oct 24 11:21 UTC] No.41878330[source]▶
    Aren't a lot of old TVs 'live chassis' as well as using very high voltages?
    replies(1): >>41885476 #
    15. maayank ◴[18 Oct 24 11:48 UTC] No.41878491{4}[source]▶
    How do you discharge them safely?
    replies(2): >>41878696 #>>41884797 #
    16. i_am_proteus ◴[18 Oct 24 12:18 UTC] No.41878696{5}[source]▶
    The correct answer is "bleeder resistor."

    The other answer is "pliers."

    (Make a connection across the terminals that have a voltage difference)

    17. implements ◴[18 Oct 24 12:31 UTC] No.41878796[source]▶
    Some older flat panels use “cold-cathode fluorescent display backlights” and they’re driven by a high-voltage inverter, I believe - so it’s still a good idea to be wary.
    18. avidiax ◴[19 Oct 24 00:57 UTC] No.41884797{5}[source]▶
    If the maximum voltage is within range, a neon line tester with the button grounded should work well. When the light goes out, the remaining voltage is below the sustain voltage of the neon lamp.

    That kind of tester is usually built into a screwdriver and often comes free with some electrical items. They are maybe $2 otherwise.

    19. mixmastamyk ◴[19 Oct 24 03:38 UTC] No.41885476{3}[source]▶
    For faster startup, yes.