help with capacitors - Page 1
Forum section: electronics / beginners

author: sviesusisalus
author_rank: Newbie
timestamp: October 06, 2019, 04:58:24 pm
content: Hello,got dead motherboard. as in most cases these die because of blown caps, so i wanna try to repair. But got a problem knowing all the specs that might be wrong with selecting capacitor.Capacitors are as listed (seen in screenshot):5KS28 560uF 6.3v - 17 pcs.5KS27 100uF 16v - 6 pcs.5KS35 270uF 16v - 2 pcs.These capacitors seem to be polymer ones, but i can't find such in my local parts store. Are the standard electrolytic ok in this case?And maybe you know who manufactured these seen in screenshot so i can try getting exactly the same? tried googlin' but no result.Electrolytic capacitor blows the top and bad one can be seen. Is it possible to visually identify bad polymer capacitors?

author: wraper
author_rank: Unknown
timestamp: October 06, 2019, 05:07:19 pm
content: 1. Time when motherboards died mostly because of bad capacitors is long gone. 2. Why do you assume that problems with aluminium electrolytic capacitors are applicable to polymer capacitors? Do you see bulged vent on top, no? Because there is no went or liquid electrolyte to evaporate to begin with. 3. No, you cannot replace polymer capacitors with aluminium electrolytic. 4. You did not even mention what fault it has but are happy to replace the parts.

author: sviesusisalus
author_rank: Newbie
timestamp: October 06, 2019, 05:18:58 pm
content: stripped to bare minimum, it just shows 0 signs of life.PSU is fine.

author: wraper
author_rank: Unknown
timestamp: October 06, 2019, 05:22:27 pm
content: If there are no signs of life, it's very unlikely to do anything with capacitors for sure.

author: mariush
author_rank: Super Contributor
timestamp: October 06, 2019, 06:01:57 pm
content: Say the model of the motherboard. I guess it's an Asus, as the capacitor drawing on the motherboard has the negative side of the circle on the positive side. The model is usually written somewhere between expansion slots, and sometimes there's a revision number in a corner of the circuit board.Grab a digital multimeter and test the power supply, make sure it outputs 5vSB (stand-by) when shut down.Then put the meter in continuity mode and test all fuses that are on the motherboard. If you don't know what a fuse is, a good example of one is below that 10 pin USB 2 header, that tiny component with a p and a 15 written on it - which probably translates to "polyfuse, 1.5A trip point" or something like that.If you don't get continuity over a fuse that can be a sign that something after that fuse died, shorted out or consumed too much power and you should look in that direction for a fault.Most likely, the motherboard is dead because a mosfet is dead, or a voltage regulator is dead.You have a bunch of mosfets under the heatsink near the CPU, you should have some mosfets by the 24pin connector, there's some mosfets in the picture you uploaded, those Nikos po1038 in the left corner of the heatsink (p06 and p07, p09,p10)Those you can test with the meter in diode mode. You need to figure out if it's n-channel mosfet (most often) or p-channel mosfet and which pin or pins are the gate, which are drain and which are source - drain and source are usually connected to wide thick traces, gate is usually a lonely pin with a thin trace.This gives a decent explanation on how to test a mosfet:This shorter one made by a EEVBlog member says something similar :Basically, on the motherboard you should not have a short between the drain and source pins of a mosfet, or between gate and the other pins.Here's an example of a motherboard with a shorted mosfet (he used continuity mode to find a short between the leads of the mosfet) :Jump to 2:45 if you're impatient:And to answer the original question, those polymer capacitors are made by Apaq and they're most likely fine. It's very very rare they die or fail.

author: thedoc298
author_rank: Contributor
timestamp: October 06, 2019, 06:03:58 pm
content: Every board I have worked on that ended up having bad caps, was showing problems before it finally died. Like takeing several trys to boot, shutting down for no reason and other wierd problems. So unless you see bloated caps I sure would not waste my time.

author: sviesusisalus
author_rank: Newbie
timestamp: October 06, 2019, 07:20:46 pm
content: xe xe, viewed the same videos you just postedAsus C60M1Iwill run down the same tests you just mentioned as soon as i get the moment.all caps are polymer. so as wraper mentioned there will be nothing visual.

author: sviesusisalus
author_rank: Newbie
timestamp: October 12, 2019, 10:51:44 am
content: Sadly my multimeter does not have continuity mode.Found two PA102FDG mosfets which do not have resistance between drain and source.Also found several P0903BDL and five of them have resistance 157 Ohm, 16 Ohm, 180 Ohm, 120 Ohm.Others had resistance about 3k-4k Ohm.So i assume those five that had lowest resistance should be replaced?

author: mariush
author_rank: Super Contributor
timestamp: October 12, 2019, 12:14:34 pm
content: The 16 ohm one is suspect. The others is debatable.You'd know for sure if you remove them from the board and measure them separately.Keep in mind that if a mosfet died, it may have killed the vrm controller that controls it as well ex sending 12v through the gate pin back towards the controller which controls those 4 mosfets.Continuity mode is just resistance measurement with sound if the resistance is less than some value, let's say around 10 ohms, it varies from meter to meter.

author: sviesusisalus
author_rank: Newbie
timestamp: October 12, 2019, 01:45:45 pm
content: desoldered that low resistance mosfet (PQ10 in screenshot). seems to be fine out of board.Yes, my soldering skills and tools are laughable. Yes i ripped the pad off. Wire will work just fine there.PQ10 and PQ9 are the same model.A hint maybe what should i be looking for next ?