Bad cap replacement question - Page 1
Forum section: electronics / beginners

author: stojke
author_rank: Regular Contributor
timestamp: August 19, 2015, 06:38:35 pm
content: Hi guys, I have a question about capacitors in power supplies.I have an LCD monitor that refuses to power on, cycles power on where it blinks for a second and turns off. When I opened it and removed the shielding and processor and power supply board I noticed that the mains capacitor and some other ones were completely busted (bulged, leaked).I have managed to find replacement capacitors for all the common value ones (470uF, 220uF, 680uF) but I can not find an replacement for the big bad 120uF 400V cap anywhere.I have managed to find an capacitor with similar values - 150uF 400V and in various old power supplies some 330uF 400V and 470uF 400V caps.My question is, can I replace the dead 120uF 400V power supply with an similar value capacitor such as 150uF 400V ? Thanks.Here is a photo of the PCB (delta electronics) :

author: wraper
author_rank: Unknown
timestamp: August 19, 2015, 06:50:09 pm
content: QuoteYes you can. Also, if wasn't going to do this anyway, replace all of the remaining Capxon capacitors too. Excluding capacitors on the mains side, all other capacitors must be of LOW ESR types. General purpose capacitors will last a few months at most.

author: gilbenl
author_rank: Regular Contributor
timestamp: August 19, 2015, 06:52:28 pm
content: For most situations- Capacitance can be ~ +/-10% or so. Voltage rating can be greater than or equal to what was in there. Don't go lower on voltage.If the exact values cannot be found, you're almost always safe going slightly above either rating. Also, its good practice to try and match temperature ratings as well.

author: stojke
author_rank: Regular Contributor
timestamp: August 19, 2015, 07:00:13 pm
content: I see, thank you guysI have also wrote down the values of the other capxon caps as well, planning on replacing them. I have found Low ESR types and also 105c rated ones. They will cost around $1 for the lot. But the 120uF (150uF) 400V costs around $5, so he is pretty pricey.Will report what happens after operation.

author: stojke
author_rank: Regular Contributor
timestamp: August 21, 2015, 08:41:51 am
content: Hi guys. The replacement capacitors have been installed.The 120uF 400V non standard one was replaced with an 100uF 400V capacitor. The monitor powers on and works normallyThanks for the help!

author: wraper
author_rank: Unknown
timestamp: August 21, 2015, 09:08:21 am
content: Quote from: stojke on August 21, 2015, 08:41:51 amYou had better replace in with 150uF capacitor. If not having the right value, increasing capacitance to the next higher value is proper way. Anyway, if using lower capacitance, I would at least check the datasheet if ripple current rating is not lower than original.

author: Gyro
author_rank: Super Contributor
timestamp: August 21, 2015, 09:50:24 am
content: Although if your mains voltage is towards the upper end of its universal input voltage range (eg, 230V) then you are probably fine for now. The HV capacitor will have been sufficiently rated to handle the increased current demands at the low end of the input range.

author: stojke
author_rank: Regular Contributor
timestamp: August 21, 2015, 10:10:21 am
content: The 150uF capacitor was also hard to find. The one I wanted to use was from an Xbox power supplyHere in Serbia we have 230V mains voltage. So far the monitor works with out problems.