Please help settle a debate for me. Blown caps

[16k_zx81]

I appear to be finding myself in a debate about the possible effects of blown caps.

In your experience, will a board function if one or more caps is blown?

Have thou ever seen a cap fault have an effect on a machine's speed?

Thanks

Jim

 

[acscva]

I have seen blown caps do some really odd things. Intermittent lockups, power down, run slow, blue screens, etc.

Just had a customer yesterday with intermittent powering off. He previously had the caps replaced and now I am recommending to just replace the PC as it is about 7 years old. It is only a fax server for their proprietary software program.......

 

[Markverhyden]

The caps thing is not always a go/no go situation from my experience. I've seen machines where they are literally split/leaking and the machine still boots.

Generally I seem to see that the machine starts behaving erratically. Taking a long time to boot, hanging/crashing after running for a while. Sometimes they will come up and other times not. Now these are all machines which I could see split/swollen/leaking caps.

 

[TechLady]

Same here; I've seen plenty of them. They can do the weirdest freaking things to a computer. I've got one on the bench right now that has caps about to leak and it still boots, and an client of mine had them fully blown and it was still booting and acting fine (though more often they don't act fine).

 

[Bryce W]

An old Technibble article with me diagnosing bad caps:
http://www.technibble.com/the-issue-is-not-always-what-it-seems-my-humbling-experience/

 

[nlinecomputers]

I appear to be finding myself in a debate about the possible effects of blown caps.

In your experience, will a board function if one or more caps is blown?

Have thou ever seen a cap fault have an effect on a machine's speed?

Thanks

Jim

Some caps can still electrically function even if they are leaking. And some will completely fail while other will have intermittent faults.

Speed can be effected if the caps are part of the system timing circuits. If caps fail to hold a charge then the transistors that gate from there current feed can fail to open or close.

 

[YeOldeStonecat]

I've seen all sorts of situations.

I've seen computers still running and they've have bulging and even leaking caps. So yes a computer can still run with failing caps.

And I've seen them lock up, hang at boot, reboot on their own, blue screen, run slow, simply lock up hard, lock up soft (screen basically unresponsive by cursor might still move), all sorts of symptoms. I've seen them exhibit the above behavior with slightly bulging or leaking caps, to fully blow burst and leaking caps.

 

[Krynn72]

I appear to be finding myself in a debate about the possible effects of blown caps.

In your experience, will a board function if one or more caps is blown?

Yes. A lot of it depends on where they are and what components they're regulating. Also as nlinecomputers has said, sometimes they can still be somewhat functioning, at least for a little while.

Have thou ever seen a cap fault have an effect on a machine's speed?

Yes again. I had a customer who came in with a issue where her pc could take 20-30 mins to boot up. It would eventually work though. Once it was booted, it would either perform reasonably well, or extremely slow. Replaced a single blown cap and it got up and booted in < 1min and ran nice and stable.

Anytime a customer starts describing really strange issues that don't fit my expectations of common failures, I check the caps. Its saved me, and my customers a lot of time and money on several occasions. If its weird, check the caps.

 

[peachypc]

Same here. YMMV
I have had computers come back 5 years after pointing out bloated caps to a customer ( I always note the inside of the computer with a dated label/tag). They may work fine for years before developing a problem. if ever.
Most of the time however they come in with intermittent hang or reboot issues and when removing the cover, the caps kinda tell the story.
Bottom line is when you see them, run the MB through the paces. If it passes, note it, point it out, and move on.
If a business machine probably just go ahead and replace it.
Many home users will prefer to replace it to rather having to "worry" about it. Some opt for a MB swap while others have just found an excuse for a new machine.

 

[NYJimbo]

The other side to this is when a machine comes in and its not booting, you observe one or more bad caps, but you cannot determine the fault is because of the bad cap and you just call it based on the visible bad cap:

For example, desktop came in not booting. Went through all diags, swapped ram, PSU, checked all ports/connections, CMOS batt chec, flush cmos/bios, remove all peripherals, etc but still cant pin it down. Noticed one bulging cap.

So since I now eliminated all removable components or swapped them and I see the bad cap I am going to call it based on the bad cap and go for a mobo replacement (unless the cap is a easy replacement, but that sometimes is a waste of time).

Sure, it could be a borked BIOS, some short somewhere else, bad I/O slot, etc, but since my diag points to "must be mobo" I am calling the cap as the fault and that ices the mobo replacement and I move on.

Once I see something like a bad cap and the mobo appears to be at fault from the diag I cant waste time assuming its something else since I cannot eliminate the bad cap from the diags.

 

[joydivision]

I had an old Dell a few months back on the bench. It was running oddly for no reason, it was slow but when I did a full diagnostics everything passed. I then decided to check for caps and sure enough one of the big caps near the processor had popped.

The point of capacitors is to store power so a component can access it instantly so if one of these are faulty the motherboard can easily work ok it is only when that power is suddenly needed you will get the unusual behaviour such as lock ups.

 

[Altster]

Generally when a desktop computer comes into the shop for repairs (and I am here) I will take a real good look inside to see if there are any blown / domed caps anywhere on the main board. I usually find them either near / around the CPU and / or around the memory sockets. Of course I listen to the problem(s) that the client may be having with the computer.

If I find any, I immediately advise the customer of the potential problems. If the hardware is older (than dirt most of the time) we do our best to upsell to a newer computer if possible.

 

[coffee]

The point of capacitors is to store power so a component can access it instantly so if one of these are faulty the motherboard can easily work ok it is only when that power is suddenly needed you will get the unusual behaviour such as lock ups.

Interesting....

Capacitors are used in a variety of ways. The most usual way is that they actually act as power or signal filtering. The problem with the idea to use a cap as a power source is that it will discharge in milliseconds or less.

Caps filter a signal or a power source. They are not intended as a quick "backup" of power. For instance, changing from AC to DC can be performed by caps. Although a better way is to use a bridge rectifier circuit (or power transistors) which is made up of 4 diodes. However, after conversion there is noise present in the signal and caps do a great job of filtering the noise out.

Caps on a motherboard are never used as a "source" of instant power as one normally views it. They are used to clean up dirty electrical signals. When the cap actually goes bad it will actually interrupt the power in a circuit. Of course this depends on the type of circuit it is in . If for example it is filtering a dirty signal as in a power supply ( in parallel)you can still get a 5volt, -/+ 12 volt signal but it will not be a clean signal. Therefore, That unclean power can play havac on digital components. In the case of rectifiying a signal to the processor (in series) it can fail in an open state and prevent the actual circuit from running. This is because the cap is in series with the other components and thus fails in an open state and prevents any signal from making it to the next circuit.

Caps typically fail in two general ways, They either dry out or they 'burst' and leak.

coffee

 

[brandonkick]

Caps can and do also go bad without displaying visual symptoms. If their equivalent series resistance increases too far, they are junk. Likewise they can also experience a capacitance shift which can cause problems.

More often then not I'd replace ones that are visibly leaky or crowing. Beyond that unless it is a rare or expensive board you are probably better off just replacing it. By the time you figure in parts and labor it makes more sense just to replace the board.

 

[PcTestCard.com]

Sometimes, damaged capacitor(s) will let the PC working correctly.
Most of time, the computer will have problem of freezes, blue screens...etc.
Or having problem finishing the fresh installation of the Operating System.

Hope this helps.
Bill
Tech Manager, WPTinc.