# A PC diagnosis and cure



## Foxbat (May 14, 2019)

I’m posting this because it may be of help to somebody else encountering similar problems.

Disclaimer: I’m not a tech (PC or otherwise). All I have is a healthy curiosity, a basic understanding of electronics and a determination to uncover the mystery.

And so our story begins…
I have an old PC running XP (still my favourite MS operating system). It’s not connected to the internet and I use it for stuff like writing and photo editing. There are no temptations to simply surf the net when using this machine and that’s why I like it.

A few weeks ago, it began to show some strange behaviours. Often, it wouldn’t boot up and would take a few tries to get it going. When it did boot up, it sometimes crashed. These characteristics got progressively worse over time, rendering it unusable. I decided to investigate rather than ditch.

Through some basic trial and error, I noticed that if I shut the power off at the mains for a few seconds and then back on, it would often boot up straight after. It still tended to crash a lot unfortunately.

Then I noticed something else. If I knocked the power of at the mains for much longer than before, it would take between 5 and ten minutes before the PC would power up. I began to suspect a capacitor. As I thought more on this, I reasoned that a faulty capacitor in the power supply could be causing voltage spikes and crash the machine. A capacitor is often used to smooth out voltages.

trivia note: A capacitor is normally filled with paper that is impregnated with an electrolytic solution and can dry out over a few years, diminishing the component’s ability to do its job. It’s also worth noting that if you get the polarity mixed up when fitting a capacitor, it can blow and leaving a mess like somebody had just gone amok with a chainsaw at an origami convention.

It all seemed to make sense.

The time delay would also fit in with my theory. A capacitor along with a resistor in series can be used to create a time delay (capacitance*resistance=time in seconds). A faulty capacitor could also be generating a high resistance. By switching off for a few seconds, I was discharging just enough to let the capacitor do its proper job. By leaving it off any longer, the capacitor/resistance combination could be creating a large time lag.

At this point, I bit the bullet and bought a new power supply for £20. It’s now installed and the old machine is running as smooth as a baby’s behind – in fact, I’ve never seen it boot up so quickly in years.

Of course, if I’m right and the problem is a capacitor, I could have dismantled the PSU and checked every one of them. Finding and replacing the faulty component would only cost a few pence but maybe take a few hours finding it. Instead, I preferred to spend £20 and have the old PSU out, new one in and PC running within half an hour.

The downside is that the new power supply doesn’t quite fit the old case and I have to leave the lid off. Still, it’ll help with the cooling and make cleaning it a breeze. There’s nothing untoward or dangerous exposed by the lack of lid (it’s covered by the power supply), it just looks a bit unfinished. Still, I’m not complaining.


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## Venusian Broon (May 14, 2019)

You should have said Foxbat, before you bought a new one, I've got a spare power supply (I had to upgrade my PC when I got a new graphics card and the old supply didn't have enough juice.) Could have given it to you.

I'm only 20 minutes up the railway line. Sort of, I'd be leaving from Waverly.

Actually I'm coming over to Dunbar in a few weeks time to see friends that live there.


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## L.L.Lotte (May 14, 2019)

I'd say you still made the right choice replacing it. When power supplies go bad they can do serious damage to other components. You're lucky it hadn't already if you think it was voltage spikes.

I've personally witnessed a bad PSU blow up a motherboard and CPU.


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## Foxbat (May 14, 2019)

L.L.Lotte said:


> When power supplies go bad they can do serious damage to other components. You're lucky it hadn't already if you think it was voltage spikes.
> 
> I've personally witnessed a bad PSU blow up a motherboard and CPU.


Exactly what I was thinking. I feel like I dodged a bullet


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## Foxbat (May 14, 2019)

Venusian Broon said:


> Actually I'm coming over to Dunbar in a few weeks time to see friends that live there.



I'm actually in West Barns (which is on the northern edge of Dunbar). I've been here over thirty years (Dunbar originally) and I'm still classed as an incomer. Weather is glorious today and I live right opposite the John Muir Country park. life is good


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## Venusian Broon (May 14, 2019)

Foxbat said:


> I'm actually in West Barns (which is on the northern edge of Dunbar). I've been here over thirty years (Dunbar originally) and I'm still classed as an incomer. Weather is glorious today and I live right opposite the John Muir Country park. life is good



Changing subject a bit...

Are there any good public 'rocky' beaches/coastal paths just off the town? 

I would like to come down early, commune with sea and go a good walk, hopefully look for fossils before retiring for sherberts with friends in the afternoon!


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## Foxbat (May 15, 2019)

Venusian Broon said:


> Changing subject a bit...
> 
> Are there any good public 'rocky' beaches/coastal paths just off the town?
> 
> I would like to come down early, commune with sea and go a good walk, hopefully look for fossils before retiring for sherberts with friends in the afternoon!


You could start at the castle and walk around the cliffs that skirts the edge of the golf course and down to Belhaven Bay. If you do this, when you pass by the swimming pool just above the castle, look down. You'll see a rocky beach where there used to be an open air swimming pool and is currently used for the European Stone Stacking Championship. you can access this area if you want to. Also further around the cliffs, you'll see the remains of an even older swimming pool (below the war memorial).


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## tinkerdan (May 15, 2019)

Where I work we have everything from machines that run 98 to window 10 and that means that all the 98 98se Me XP 2000 and NT machines are pretty old--I'm constantly replacing power supplies and fans.

As far as replacing the damaged part(aka capacitor)--think about that origami image you created and then include your finger in the equation. And those Capacitors in a power supply are often much more dangerous.  Also capacitors hold a charge and in most cases after you remove the power that charge will begin to dissipate; however that doesn't mean that you should assume after any period that the thing has no charge. You will be messing with mighty forces.

Where I work, I've worked with design engineers who have to work with prototype boards--open bare boards. One  morning I was enjoying the quiet in my cubical and the engineer in the next was working away at a small board when I heard what sound like a firecracker. The engineer was Italian and spoke several different languages--French, Spanish, Russian, Latin and I recall hearing a cascade of curse words in several of those. When I was certain it was okay to look over the wall, I could see that he had gotten lucky and only had  a blackened forefinger. It was a  tantalum capacitor--one that looks like a chiclets gum only smaller.

Many times the cap is holding the current constant; so if something surges or draws of current it attempts to stabilize the current for specific parts. That way it prevents the device from browning out. When you warm boot a machine through the reset button or any other boot those caps remain charged. When you cold boot--complete power down--the caps have time to discharge slowly so when you boot up again they will act differently because they have to charge initially.  The point I',m leading up to is, yes a cap can go bad and make things not work, however it might have gone bad while trying to protect your equipment from something else that went wrong. So--better to change out the power supply with a new.  

The same may hold true when the motherboard starts frying capacitors. You can chase down which one; however that might not fix the problem.


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## chrispenycate (May 15, 2019)

I hate, loathe and detest mending switch-mode power supplies (have I made it clear I don't enjoy it much?)

Not only that they bite - it is not infrequent to find four hundred volts between adjacent contacts - but I'd prefer to repair a heavy-duty tube (valve) amp with 650Volt HT. They're just so clever, with their stabilisers integrated into the principal power loop, until the magic smoke escapes and almost anything can have blown - rectifiers, electrolytics, FETs, isolators, and if you don't find the culprit right away i blows all the others.

But they're cheap, and lightweight, and high spec., (and made in Taiwan), so everybody uses them.

I've had to analyse a few (generally in keyboards and recording studios rather than computers - those you just junk when you can no longer obtain ready built replacement PSs), and if I never meet another it will be somewhat too soon.


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