caps in parallel

[budm]

Re: caps in parallel

You should measure the voltage on the cap to verify the polarity, some MB use the white marking/band for showing positive instead of negative, ASUS did that on some of there MB.
Read page 61 and on.

[SteveNielsen]

Re: caps in parallel

That's a good read. Thank you. There is no "figure L" though. I think they mean't figure I.

[volumetricsteve]

Re: caps in parallel

This is getting even weirder...I have more testing to do, BUT....

I got a mix of ceramic and tantalum caps, set them up in parallel, installed them in my system where I get no heat issues...in fact, almost no heat at all, the system boots fine, boots OSes, runs, jumps, plays happily, etc. I assume the caps I've installed are doing something right.

However, when I go to measure the voltage across that spot where the leads on the board are for this cap, I show no voltage. Granted, I haven't tested it without any cap there at all yet, but while the system is live...I'd think there should be some value there.

[budm]

Re: caps in parallel

"However, when I go to measure the voltage across that spot where the leads on the board are for this cap," You should check the resistance across that spot.
BTW, the cap taht gets hot, did you ever verify the polarity when it was installed?

[volumetricsteve]

Re: caps in parallel

I sure did, the polarity matches what I did, and actually all marked caps on the board face the same way, interestingly enough.

[Agent24]

Re: caps in parallel

"However, when I go to measure the voltage across that spot where the leads on the board are for this cap," You should check the resistance across that spot.
BTW, the cap taht gets hot, did you ever verify the polarity when it was installed?

x2, If you measure no voltage across it then it maybe shorted. Could be a manufacturing defect in that specific capacitor.

[volumetricsteve]

Re: caps in parallel

I wonder about that as well...but then how is my board still functioning?

I'd think a short where a cap should go could spell disaster for sensitive electronics, no?

[Agent24]

Re: caps in parallel

It depends on where the capacitor is in the circuit and what it does. Going by the value it is probably a power rail filtering capacitor of some kind. We could confirm that with a photo. This might also help determine if it's backwards.

It might not be dead shorted to cause a PSU shutdown or such, and have enough resistance to act as a heater instead of a capacitor. Just because the board works now does not mean it will keep working.

With the board powered off, check resistance across the capacitor pads. It should start out low and slowly increase as the capacitor charges up. If it stays low, the capacitor (or something in parallel with it) is shorted.

A possibility is that the capacitor was marked backwards in the factory. Very uncommon but not unheard of. I read about it happening once in the Serviceman's Log in EA Magazine.

[budm]

Re: caps in parallel

So, what is the resistance reading? The circuit may have to be activated (the voltage fed through switch (transistor/MOSFET) when certain function is required, need to find out what the function for that section of the circuit is.

"A possibility is that the capacitor was marked backwards in the factory" some of the ASUS MB did that, the bar for positive.

[volumetricsteve]

Re: caps in parallel

Wow, that's intense, good thoughts though, all around. I'll check the re...oh crap, wait I can't check the resistance because my multimeter is trashed...I'll have to see if I can track down a new multimeter but I'll check all those things as soon as I can. I should point out - specifically in reference to polarity - I put in a few tantalum capacitors (2x 220uf and 2x 15uf caps in parallel to make 470uf) based on my understanding of the polarity and they didn't explode or heat up.

recommendations on multimeters?

[budm]

Re: caps in parallel

Post #23 "However, when I go to measure the voltage across that spot where the leads on the board are for this cap, I show no voltage."
Post #30 "I should point out - specifically in reference to polarity - I put in a few tantalum capacitors (2x 220uf and 2x 15uf caps in parallel to make 470uf) based on my understanding of the polarity and they didn't explode or heat up"

Since there is no voltage present, may be that is why they did not heat or blow up.

[volumetricsteve]

Re: caps in parallel

That would make sense..but then why would the original electrolytic and replacement aluminum polymer get so hot? I'm wondering if when I put the tantalums in, I didn't create a solid connection...which would be surprising because the system seems completely fine, but I'll recheck that as well.

My plan is to measure voltage across the sections with no capacitor.
Measure voltage with the aluminum polymer, tantalum, and electrolytic.

I guess a key here would be to see if I remove the cap entirely and it still boots, chances are i messed something up..or that cap goes severely under-utilized by design.

I still need a good multi-meter though, I had a Klein tools one which was extremely faulty,(12V DC showed up as anything between 111V and 130V, constantly changing) and their customer support...left a lot to be desired.

[budm]

Re: caps in parallel

"That would make sense..but then why would the original electrolytic and replacement aluminum polymer get so hot?" Since you did not take the voltage measurement when the cap was hot and verify the voltage polarity applied to the hot cap, then we cannot tell, and right now if there is still no voltage after the cap is removed, may be the switching device is damaged and not providing the power to the circuit any more.

[volumetricsteve]

Re: caps in parallel

Ok, interesting point....I'll try and get voltage readings off one that gets hot. Although, there has been another strange development. I booted the system with no cap in the 470uf slot at all, the system works perfectly fine without it (it boots, anyways) so, that surprised me. Then, I used a little voltmeter I have (it is only a voltmeter) to measure the pads for that cap. no matter what polarity I used or which pads I used (the area has SMD mount points as well as through-hole for the same cap, I can see they're PCB'd together) I got no readings at all.

I'm wondering if it's a cap that's meant to do something in sleep mode....or something that would involve changing power states for certain devices..I'm guessing the machine-state needed to put voltage on those points could be something other than power-on. I'll try other boards to see if I find the same behavior. Thanks again for your interest.

[budm]

Re: caps in parallel

You can also connect the cap that gets to hot to a 9-VOLT battery to see if it gets hot.

[retiredcaps]

Re: caps in parallel

I still need a good multi-meter though, I had a Klein tools one which was extremely faulty,(12V DC showed up as anything between 111V and 130V, constantly changing) and their customer support...left a lot to be desired.

If you want recommendations on a new multimeter or suggestions on how to fix your existing Klein one, start a new thread in the Equipment Usage, Soldering, Techniques, and Reviews section and I will have a look at it.

Currently, I'm interested in fixing multimeters of all kinds so I would be happy to make suggestions. Be sure to post a clear focused picture of the Klein meter taken apart so I can see the pcb and insides. Also post the model number.

[Agent24]

Re: caps in parallel

Ok, interesting point....I'll try and get voltage readings off one that gets hot. Although, there has been another strange development. I booted the system with no cap in the 470uf slot at all, the system works perfectly fine without it (it boots, anyways) so, that surprised me. Then, I used a little voltmeter I have (it is only a voltmeter) to measure the pads for that cap. no matter what polarity I used or which pads I used (the area has SMD mount points as well as through-hole for the same cap, I can see they're PCB'd together) I got no readings at all.

Could be the capacitor was shorted, and blew whatever supplies power to it so now you get nothing. If you test all your ports and onboard functionality you may find something no longer works.

I'm wondering if it's a cap that's meant to do something in sleep mode....or something that would involve changing power states for certain devices..I'm guessing the machine-state needed to put voltage on those points could be something other than power-on. I'll try other boards to see if I find the same behavior. Thanks again for your interest.

Near impossible to know exactly what it does without a schematic or at least a photo.

[volumetricsteve]

Re: caps in parallel

You can also connect the cap that gets to hot to a 9-VOLT battery to see if it gets hot.

I was considering doing exactly that, maybe in parallel with an LED so I could see how the light reacts when I took the battery away.


@retiredcaps

I appreciate it, but alas, any picture I could provide would be anything but focused. It would be interesting to see why this one went as insane as it did, but in the interests of focusing my time, I'll go get a new one.

@agent24

I checked and rechecked for shorts....unless the cap was shorted internally..I can't see where that would be the case. I'm with you on the blowing the supply part, but I can populate every PCI slot and power video cards through AGP....I forget what the signal voltage of IDE is, but I haven't tested the IDE ports yet, though I feel like a signal-power path wouldn't have a huge honking cap built into it...but I'm no expert.

The cap in question is right next to the ATX power connector, it's also next to the ram banks (which are RIMM, so they guzzle insane amounts of power for the time)

The attached photo I threw in should show a few points, also my horrible mspaint skills :P


EDIT:

did I mention that I measured the voltage both my aluminum-polymer and my tantalum caps with no sign of voltage in either direction? I should also mention that my tantalum caps are SMD-type, so I did some creative soldering to get copper wires on the terminals and then solder those into the board. So far, no fires.

There is also what appears to be a voltage regulator next to the site of the 470uf cap that gets pretty hot, but the surrounding PCB feels cool. I thought it would be a stretch for the heat of the vreg to go through the pcb (which feels cool) and then get back into just that cap, while everything else around it remains cool. As an experiment, I put a little heatsink on it to see if that changes things.

[reaper57]

Re: caps in parallel

You said you had some boards that worked fine, right? Well, if you still have access to them can you check the voltages on them? It might just be, as previously mentioned, conected to a rail that isn't used all the time.