pc - determining cause of death

tvout · 03-11-2006, 20:16

Hi all,
I've taken on a dead PC and wondered what people might suggest be the faulty item...

Here's what happens...

Press the power on button, the PSU fan spins for a second so does the CPU fan but both stop. The motherboard has a small amber led labelled 'DIMMLED' which I know is something to do with the memory (although I would think a memory problem would result in bios beeps...)
anyway, that led stays on but everything is dead...
If you hold in the power button the led will go out as if forcing a hard reboot.

My thought is the PSU...any other ideas...?

If it was something to do with the mobo would that stop the PSU fan?

What is everyone's thoughts?

MadGamer · 03-11-2006, 20:19

Yeah if the PSU blows, then it can take out the mobo and other components as well

Scrubbs · 03-11-2006, 20:25

Possibly the power button not latching, any change if you keep your finger on it?
oops didn't read the whole thread

Ok If possible you are going to have to start swapping components,
start by disconnecting everything from the mobo and reconnect one at a time

I have had a pc refuse to boot because the floppy drive was U/S and prevented the pc from working

MovedGoalPosts · 03-11-2006, 20:27

If the PSU has blown, then you'd have no activity at all on the PC, even the fans and LEDs, unless it's just the one output from the PSU.

First thing I'd be looking at is the Hard Disk, will that work in another PC, or vice versa can you try the PC with a different HD? It's probably going to be a process of trial and eliminationof components from one working PC to another that isn't.

I assume you can't even get it to boot to the BIOS screen?

tvout · 03-11-2006, 20:28

Cheers for the thoughts.
I'm going to try a PSU tester and see what happens.
I have tried holding the power button in when starting it and still does the same...

marky · 03-11-2006, 20:30

Ive had simlar results from a dead memory stick

03-11-2006, 21:25

Quote:

Originally Posted by tvout

Hi all,
I've taken on a dead PC and wondered what people might suggest be the faulty item...

Here's what happens...

Press the power on button, the PSU fan spins for a second so does the CPU fan but both stop. The motherboard has a small amber led labelled 'DIMMLED' which I know is something to do with the memory (although I would think a memory problem would result in bios beeps...)
anyway, that led stays on but everything is dead...
If you hold in the power button the led will go out as if forcing a hard reboot.

My thought is the PSU...any other ideas...?

If it was something to do with the mobo would that stop the PSU fan?

What is everyone's thoughts?

Just resolved a similar problem and it was a knackered 9700 Pro.
Although on this the fans spun but very fast, no post nothing.

tvout · 03-11-2006, 21:39

I've just popped out to Maplins and bought a PSU tester...

This is what happened...

Plugged power lead into PSU, plugged 20 pin connector into tester. It beeped, lit two leds at first:
+12V
+5VSB

After a second the +12V led died, leaving only the +5VSB lit
The other 5 leds didn't light (+3.3v, -12v, PG, -5v, +5v).

Sounds like it's a new PSU...

---------- Post added at 20:39 ---------- Previous post was at 20:26 ----------

One thing I've noticed that I hadn't seen before. On the back of the PSU there's a small hole for a small DC jack plug (12v) and a square 4 pin connector from the PSU onto the motherboard which says AUX12V & 12VATX next to it? Is this some kind of extra power output from the PSU which is somehow monitored by the mobo?
Would it matter if I bought a new PSU which didn't have this extra connector, just the 20 pin one?

MovedGoalPosts · 03-11-2006, 21:44

A lot of the latest motherboards need that extra 4 pin connector. Ignore it and your PC won't boot (took me ages to work out why mey new PC build didn't work, 'cos I'd missed that one). Most modern PSUs should have the connector as standard. My moterhboard manual describes it as an EATX12 V power plug.

03-11-2006, 22:28

The 12 volt on the back would have fed a pair of speakers giving them power. Some psus come with 2x12 volt 4 pin and better psus come with 2 x 6 pin plugs for pci graphics also.These normally will have 24 pin atx instead of 20.If your board had a 4 pin connector you should use it or the cpu wont power up correctly if at all

tvout · 03-11-2006, 22:39

Cheers guys. I'll look for a new PSU tomorrow.

SMHarman · 03-11-2006, 23:28

Mine died like this it was a new cpu that was required to fix it.

AntiSilence · 04-11-2006, 04:15

Quote:

Originally Posted by Rob C

If the PSU has blown, then you'd have no activity at all on the PC, even the fans and LEDs, unless it's just the one output from the PSU.

Not strictly true. The PSU provides more than 1 supply rail... For example, there's a +5V rail, a +12V rail, and some other (including some negative rails, like -12V).

Each rail supplied power to different parts of the PC. The +12V rail, for example, supplies HDD's and GFX cards etc. If only part of a PSU has blown, the rest may work. EG, the +5 rail may still work.

PC power supplies are switched mode, and are really nasty beasts to fault find on, since all outputs only work correctly under load. Nasty.

tvout · 04-11-2006, 11:35

Quote:

Originally Posted by AntiSilence

Not strictly true. The PSU provides more than 1 supply rail... For example, there's a +5V rail, a +12V rail, and some other (including some negative rails, like -12V).

Each rail supplied power to different parts of the PC. The +12V rail, for example, supplies HDD's and GFX cards etc. If only part of a PSU has blown, the rest may work. EG, the +5 rail may still work.

PC power supplies are switched mode, and are really nasty beasts to fault find on, since all outputs only work correctly under load. Nasty.

Spot on. That would explain it. The only activity on the motherboard was a DIMMLED', DIMMs require 5v usually (well I know some are different) don't they? They also said that the monitor had power (on pass through). I used the tester on the 4 pin molex connectors to the HD/CDROMs etc and they didn't indicate any power at all on the tester.
As I say the only led that lit from the PSU to the motherboard connector was the +5V one, suggesting that 12v etc. rails in the PSU had blown.
When I spoke to the witnesses :o), well, owners they said they hadn't heard the fan start up the last few days...
At a guess could the fan have been the PSU one, being thermo-controlled and this not starting up led the PSU to overheat and cause damage?

Does this all sound feasible?

AntiSilence · 04-11-2006, 16:32

When my last PSU blew up, the fans in my PC stopped working, the power LED was still on but the system was dead.