Motherboard low ESR vs general purpose

[a23d56]

I have an old PCChips M810L motherboard.

I bought low ESR caps to replace all the big caps (1000uF and up), did that job, and the board is running OK. I haven't replaced any small caps yet, there are about 30 in all, a mix of 16v 100uF and 25v 22uF.

Just wondering if I can get by with general purpose caps for the small ones, since they are cheaper. I understand you want low ESR near the power supply, but is that necessary for all caps on a motherboard?

It's not like I'm going to sell this thing to a hospital for a life critical application. I'm just playing around with a soldering iron to see if anything smokes or explodes.

[Topcat]

Re: Motherboard low ESR vs general purpose

those smaller ones many times are GP caps. They shouldn't need to even be replaced, but if you're feeling adventurous, GP stuff will typically be fine

[a23d56]

Re: Motherboard low ESR vs general purpose

those smaller ones many times are GP caps. They shouldn't need to even be replaced

I thought of getting an ESR tester to check them, but then I read you can't reliably test them in circuit. If I take them out, I'll replace them while I'm at it.

But you're saying small caps are less likely to fail?

Why?

[cheapie]

Re: Motherboard low ESR vs general purpose

I thought of getting an ESR tester to check them, but then I read you can't reliably test them in circuit. If I take them out, I'll replace them while I'm at it.

But you're saying small caps are less likely to fail?

Why?

Probably because the electrolyte is simpler (and easier to get right) for GP caps.

[mariushm]

Re: Motherboard low ESR vs general purpose

They're not used in a circuit where there are high currents, lots of power consumption, they don't heat up that much.

Capacitors near the processor are under more stress, high currents, self heating from the internal ESR, heating from the heatsink of the processor and the ICs that convert 12v to the voltage used by the cpu (usually 0.8-1.3v)...
In order to have a very low ESR some capacitors have electrolyte made with chemicals that are more liquid so in time they dry up and go bad faster while smaller capacitors that don't have to be so good can use more stable chemical formulas (more paste like electrolyte etc)

[Agent24]

Re: Motherboard low ESR vs general purpose

Bear in mind though that some of the really cheapo ones will die pretty quick no matter the type or application circuit.

[a23d56]

Re: Motherboard low ESR vs general purpose

Bear in mind though that some of the really cheapo ones will die pretty quick no matter the type or application circuit.

The small ones on this board are Luxons. Are they cheapo?

[mariushm]

Re: Motherboard low ESR vs general purpose

It's not a great manufacturer, but it's better than random chinese ones. Like I said, if they're not used for serious stuff, they're going to be good enough. I wouldn't worry about them.

[a23d56]

Re: Motherboard low ESR vs general purpose

if they're not used for serious stuff, they're going to be good enough. I wouldn't worry about them.

I have two of these boards, identical, from the same source. The second board, I've not done any work to yet. Funny thing about the second board is, it will not retain CMOS settings even with a good battery. And it seems to drain a battery if I leave it in.

There are a couple of small caps near the CMOS battery, so I think I will try replacing them and see if that helps. Looks like Mouser has a good deal on Kemets if I buy quantity 50.

[Agent24]

Re: Motherboard low ESR vs general purpose

Yeah, probably something shorted on the battery circuit then

[a23d56]

Re: Motherboard low ESR vs general purpose

I replaced the small caps too, but the problem remained. Then I looked at the circuit, mostly surface mount, tiny components. With no electronics training, it's over my head. But I do know enough to see the battery +ve goes to a 1k resistor. That checked OK. Next stop is a tiny 3 leg thing marked "352." Googling and reading data sheets led me to believe it's a P channel mosfet. If true, my multimeter indicated a short from source to gate.

I found a replacement part at Mouser and ordered a few. It seemed crazy to try and replace it, they are so tiny I can barely see them! But with the help of a small magnifying glass, I finally got the bad one off and the new one soldered in.

The hardest thing was reading datasheeets and trying to understand mosfet gate, source, and drain, and getting the right part ordered. Beginner's luck I guess, it's all working now. Without standby +5v power, the voltage from drain to ground is 3.0, as it should be (powered by battery). With +5v standby on, the voltage from drain to ground is 0.05, indicating source to drain is open, and the battery is isolated from the circuit, as desired.

What puzzles me though, is the voltage from gate to drain. Gate to ground is 5.0 (standby +5v). As mentioned previously, drain to ground is 0.05. So it seems like gate to drain should also be approx 5.0. But it's only 2.1. Seems like I'm missing 2.9v somehow.

There are some diodes and other things in the circuit, and I can't figure it all out. I guess if the battery doesn't explode, it's all good though.

[Per Hansson]

Re: Motherboard low ESR vs general purpose

Job well done! Isn't the feeling great when you find the reason for a problem like this?

[a23d56]

Re: Motherboard low ESR vs general purpose

I never considered working with surface mount components until I watched a Dave Jones youtube tutorial where he does some surface mount soldering and says "even Stevie Wonder could do this!" I really didn't know what I was doing, but that's never stopped me before.

[Agent24]

Re: Motherboard low ESR vs general purpose

I never considered working with surface mount components until I watched a Dave Jones youtube tutorial where he does some surface mount soldering and says "even Stevie Wonder could do this!" I really didn't know what I was doing, but that's never stopped me before.

I thought they were impossible too the first time I saw them, even after watching some Youtube videos (https://www.youtube.com/user/SolderingGeek) but then I gave it a try, and I was surprised. I think a lot comes down to technique. The 0.3mm solder helps too, though.

I've done chip resistors and caps down to 0402 size so far, and ICs too, like QFP and TSOP. Get a couple of solder bridges on those but wick fixes that easily.

[SteveNielsen]

Re: Motherboard low ESR vs general purpose

That's because we're here to fix things rather than buy new things to replace them.

[a23d56]

Re: Motherboard low ESR vs general purpose

Learning how to fix things requires effort. All that hot new tech you buy this year will be "obsolete" (from your viewpoint) in two or three more years.

Once I figured out that hot new tech is a never ending treadmill, I stopped wasting money on it. Now I get old stuff for little or nothing (cause nobody else wants it now) and fix it up. Saves money, and it's more fun.

[Rulycat]

Re: Motherboard low ESR vs general purpose

It's also way better for the environment to fix than replace. Just like how I keep my gas-guzzling (well it does 35MPG but for a city box car that's a gas-guzzler) on the road even though it's 10 years old - it's better for the environment to burn the fuel than get a new car.