5 ms·

I've repaired several TVs and monitors, LED lamps, etc. just by replacing bad capacitors, and in a few cases some diodes too, so it's worth trying especially on

I've repaired several TVs and monitors, LED lamps, etc. just by replacing bad capacitors, and in a few cases some diodes too, so it's worth trying especially on electronics that would otherwise be thrown away. If you see a TV/monitor going off randomly or a LED lamp starts flashing, pretty sure there are one or more defective capacitors in there. Defective capacitors are a common plague in modern electronics, and the culprit is always the capacitor: the market is literally invaded by rubbish quality capacitors, and swapping a bad quality one with another bad quality one guarantees it will fail again one day, so buy only reputable parts from reputable vendors; avoid online purchases of branded parts from unknown resellers (pretty sure that 99.999% of Nichicon or ELNA capacitors sold by any Aliexpress, Ebay, Amazon, etc. sellers are relabeled fakes); pay them more but pay them once. A web/image search for "counterfeit capacitors" works better than 1000 words. Anyway, when shopping for (hopefully genuine) electrolytic capacitors, respect also the temperature ratings. Capacitors mounted into a power supply are exposed to higher temperatures, so always choose the 105c degrees type. Capacitance is usually not critical; electrolytic capacitors accuracy can be worse than 20%, and that's not a problem because they're not required to be accurate for their job, so if you don't find the exact value, you can safely swap the part with one with slightly higher capacitance; same for the rated operating voltage which can be higher (not lower!). Low ESR rated ones are preferred; if you can, buy them instead of generic ones.

eurasiantiger 5y ago
Low ESR only matters for PWM filtering capacitors, such as those found in monitor backlight drivers and some switching power supplies’ secondary circuits. It is not necessary to use such capacitors on the primary side, i.e. when the large capacitor nearest to the mains input dies, just replace it with a normal electrolytic capacitor that matches or exceeds the original’s voltage rating and closely matches its capacity.
- klodolph 5y ago
  Worse yet, sometimes the circuit won't work with a low-ESR capacitor. For example, you can't put a low-ESR capacitor on the output of an LM1117, it will oscillate.
  - eurasiantiger 5y ago
    In a pinch, that could be compensated with a resistor, a few ohms would suffice… :)
yitchelle 5y ago
> the market is literally invaded by rubbish quality capacitors, and swapping a bad quality one with another bad quality one guarantees it will fail again one day Actually, even a quality capacitor will fail eventually, just not as early as the fake ones. As you have mentioned about the heat, the capacitor will be exposed to it and will fail because of it.
- Laforet 5y ago
  I have replaced more capacitors in appliances than electronics. The fact that appliances runs on higher voltages and stop/starts frequently exacerbate the heat problem. The 9 years old range hood in my kitchen is already had the start capacitor replaced twice. Whoever designed this unit decided to place the circuitry right in a hot spot, making sure that the capacitor will be gently toasted to death in a couple of years.
MisterTea 5y ago
Aye I remember bringing back a lot of dead monitors, TV's and even a cheap Pentium 4 motherboard by swapping caps. A place I worked at had a bunch of 19" Optiquest LCD monitors which ALL eventually died from a single bad cap on the power supply board. I fixed every one of those monitors, think it cost less than $10 to order the caps from digikey.
- dehrmann 5y ago
  How do you figure out which ones are bad?
  - deleted 5y ago
    [deleted]
  - derac 5y ago
    https://www.ifixit.com/Wiki/Troubleshhoting_logic_board_components https://www.ifixit.com/Wiki/Troubleshhoting_logic_board_comp...
  - squarefoot 5y ago
    Some can be easily spotted by visual inspection for being bulged just like the one in the linked article photo, others will need to be measured. Leakage (ie, when a capacitor exhibits resistive properties by conducting current also when fully charged) can be measured easily by using an analog tester or a digital one plus a few parts, while the ESR (equivalent series resistance) measurement would need a proper instrument called ESR meter. The ESR is an unwanted static series resistance the capacitor would exhibit no matter the frequency it works at, it increases with aging and it's independent from the capacitive reactance which it's related to the frequency. Therefore, the lower the ESR, the better quality or condition is the capacitor. However, you can just ignore the 2nd sentence if repairing a device would require just a bunch of capacitors; quality ones aren't that pricey, and if you find a bulged one, it is often advised to replace all capacitors employed in the same stage anyway. Some in fact can degrade without showing any visible hints of their condition.
grishka 5y ago
Huh. I have a Dell monitor that suddenly started showing these kind of smeared stripes instead of a proper picture. Took it apart, looked carefully at all the capacitors and other components on both boards, but none looked bad. Disconnecting and reconnecting the ribbon that goes to the LCD panel made no difference whatsoever. What could it possibly be?
- fouc 5y ago
  does a bad capacitor always show damage visibly?
  - MisterTea 5y ago
    Most likely it will simply NOT power on. That or briefly power on and shut off once the ripple spikes and glitches everything. In another post here I mentioned fixing Optiquest monitors. The usual issue was you would press the power button and the power LED would flah for a second and... nothing. This is because the output cap of the switching supply would cease to filter the high speed square wave that goes through the transformer. So your DC power supply is now an AC square wave supply. Of course logic circuits don't like that so they will outright fail. Sometimes there is enough capacitance via decoupling caps, ground planes on the PCB and local filter caps on the logic board so the initial power up works but once the load increases the ripple increases until it becomes AC again and everything goes haywire or shuts down.
  - hellbannedguy 5y ago
    no
  - ska 5y ago
    no. but often does.
- BBC-vs-neolibs 5y ago
  Capacitors can be bad but look perfectly fine. If there aren't many, one can just replace all of them.
- kasabali 5y ago
naikrovek 5y ago
good caps go bad, too. service lifetime is a function of temperature and time. lower the operating temp by 10°C and you double the lifespan of the good name-brand capacitor, and probably quadruple the life of the crappy generic cap.
- BizarroLand 5y ago
  Then again, if the item you are repairing is 4 years old or more, then the original caps have enough life span to justify using same quality replacements. Sure, you might only be saving 30 cents on an individual item (not counting shipping), but if its what you have on hand there's not really a downside.
riedel 5y ago
Planned obsolescence using wrongly placed capacitors is one of the few conspiracy theories I tend to believe in (I guess it is conspiracy). I also successfully repaired an old telefone system, a washing machine and an old TV 15 years ago because the same capacitors failed so frequently that even without any knowledge one would be able to Google what needed to be exchanged together with order links. However, I think manufacturers really found better strategies for planned obsolescence eg. by introducing new communication standards or turning off server and not providing software updates. So during the last 10 years I mostly threw away fully functional hardware...

eurasiantiger 5y ago

Low ESR only matters for PWM filtering capacitors, such as those found in monitor backlight drivers and some switching power supplies’ secondary circuits. It is not necessary to use such capacitors on the primary side, i.e. when the large capacitor nearest to the mains input dies, just replace it with a normal electrolytic capacitor that matches or exceeds the original’s voltage rating and closely matches its capacity.

klodolph 5y ago
Worse yet, sometimes the circuit won't work with a low-ESR capacitor. For example, you can't put a low-ESR capacitor on the output of an LM1117, it will oscillate.
- eurasiantiger 5y ago
  In a pinch, that could be compensated with a resistor, a few ohms would suffice… :)

yitchelle 5y ago

> the market is literally invaded by rubbish quality capacitors, and swapping a bad quality one with another bad quality one guarantees it will fail again one day Actually, even a quality capacitor will fail eventually, just not as early as the fake ones. As you have mentioned about the heat, the capacitor will be exposed to it and will fail because of it.

Laforet 5y ago
I have replaced more capacitors in appliances than electronics. The fact that appliances runs on higher voltages and stop/starts frequently exacerbate the heat problem. The 9 years old range hood in my kitchen is already had the start capacitor replaced twice. Whoever designed this unit decided to place the circuitry right in a hot spot, making sure that the capacitor will be gently toasted to death in a couple of years.

MisterTea 5y ago

Aye I remember bringing back a lot of dead monitors, TV's and even a cheap Pentium 4 motherboard by swapping caps. A place I worked at had a bunch of 19" Optiquest LCD monitors which ALL eventually died from a single bad cap on the power supply board. I fixed every one of those monitors, think it cost less than $10 to order the caps from digikey.

dehrmann 5y ago
How do you figure out which ones are bad?
- deleted 5y ago
  [deleted]
- derac 5y ago
  https://www.ifixit.com/Wiki/Troubleshhoting_logic_board_components https://www.ifixit.com/Wiki/Troubleshhoting_logic_board_comp...
- squarefoot 5y ago
  Some can be easily spotted by visual inspection for being bulged just like the one in the linked article photo, others will need to be measured. Leakage (ie, when a capacitor exhibits resistive properties by conducting current also when fully charged) can be measured easily by using an analog tester or a digital one plus a few parts, while the ESR (equivalent series resistance) measurement would need a proper instrument called ESR meter. The ESR is an unwanted static series resistance the capacitor would exhibit no matter the frequency it works at, it increases with aging and it's independent from the capacitive reactance which it's related to the frequency. Therefore, the lower the ESR, the better quality or condition is the capacitor. However, you can just ignore the 2nd sentence if repairing a device would require just a bunch of capacitors; quality ones aren't that pricey, and if you find a bulged one, it is often advised to replace all capacitors employed in the same stage anyway. Some in fact can degrade without showing any visible hints of their condition.

grishka 5y ago

Huh. I have a Dell monitor that suddenly started showing these kind of smeared stripes instead of a proper picture. Took it apart, looked carefully at all the capacitors and other components on both boards, but none looked bad. Disconnecting and reconnecting the ribbon that goes to the LCD panel made no difference whatsoever. What could it possibly be?

fouc 5y ago
does a bad capacitor always show damage visibly?
- MisterTea 5y ago
  Most likely it will simply NOT power on. That or briefly power on and shut off once the ripple spikes and glitches everything. In another post here I mentioned fixing Optiquest monitors. The usual issue was you would press the power button and the power LED would flah for a second and... nothing. This is because the output cap of the switching supply would cease to filter the high speed square wave that goes through the transformer. So your DC power supply is now an AC square wave supply. Of course logic circuits don't like that so they will outright fail. Sometimes there is enough capacitance via decoupling caps, ground planes on the PCB and local filter caps on the logic board so the initial power up works but once the load increases the ripple increases until it becomes AC again and everything goes haywire or shuts down.
- hellbannedguy 5y ago
  no
- ska 5y ago
  no. but often does.
BBC-vs-neolibs 5y ago
Capacitors can be bad but look perfectly fine. If there aren't many, one can just replace all of them.
kasabali 5y ago

naikrovek 5y ago

good caps go bad, too. service lifetime is a function of temperature and time. lower the operating temp by 10°C and you double the lifespan of the good name-brand capacitor, and probably quadruple the life of the crappy generic cap.

BizarroLand 5y ago
Then again, if the item you are repairing is 4 years old or more, then the original caps have enough life span to justify using same quality replacements. Sure, you might only be saving 30 cents on an individual item (not counting shipping), but if its what you have on hand there's not really a downside.

riedel 5y ago

Planned obsolescence using wrongly placed capacitors is one of the few conspiracy theories I tend to believe in (I guess it is conspiracy). I also successfully repaired an old telefone system, a washing machine and an old TV 15 years ago because the same capacitors failed so frequently that even without any knowledge one would be able to Google what needed to be exchanged together with order links. However, I think manufacturers really found better strategies for planned obsolescence eg. by introducing new communication standards or turning off server and not providing software updates. So during the last 10 years I mostly threw away fully functional hardware...