Computer will not start - not even the fan

Thread Starter

StrongPenguin

Joined Jun 9, 2018
287
We have an 8 year old PC for a radar, which does not start.

It behaves as though I needs power, because when you power on, the fan starts blowing and stops after a couple of seconds. Then nothing happens after that. Power LED is lit during the whole time.

I know there are sensing lines and OK signals. Is there any way to check if these are good?

We have tried with a different PSU which works, but no luck.

If the HDD is toast, it would not behave like this, no?
 

SamR

Joined Mar 19, 2019
3,179
Typically, you would first hear the HDD motor spin up and then the noise of the head seeking. Computer power supplies also usually have a current sense. Not an expert on this but if there is an insufficient load on the current sense the power supply drops out? Even without the hard drive, the computer should POST and go to the system configuration screen if there is a fault. You should be able to force it to the config screen by repeatedly pressing F8 (some computer us other function keys) on startup. You should at least be able to get the config screen to show. IF not, then there is seriously a problem and the power supply could be the problem.
 

eetech00

Joined Jun 8, 2013
2,292
We have an 8 year old PC for a radar, which does not start.

It behaves as though I needs power, because when you power on, the fan starts blowing and stops after a couple of seconds. Then nothing happens after that. Power LED is lit during the whole time.

I know there are sensing lines and OK signals. Is there any way to check if these are good?

We have tried with a different PSU which works, but no luck.

If the HDD is toast, it would not behave like this, no?
Try resetting bios by unplugging the AC power, then remove the battery. Wait 30 seconds. Then install the battery, then plug AC power in. Power on the computer..
 

sagor

Joined Mar 10, 2019
394
If another PSU also shuts down, then it comes down to 2 main possibilities.
1) There is a "broken" power start signal (green wire on most PSU) that comes from a front panel "start" switch. Many OEM power supplies will start up for a second or two to check voltages and such, then shut down until they get a "power start" signal.
2) You have some short of either 3.3V, 5V or 12V, usually to ground. A mis-wired connector perhaps, shorting mounting screw or something else that is drawing excessive current. Most PSU will shut down when they detect a short circuit (low voltage on sense circuit).
Try both PSU with nothing connected internally, no drives, no add-on cards - just built in video and keyboard. Try even without keyboard... If system still shuts down when you try to start, it is either the "start" signal is broken, or you may have a short in the motherboard mounting screws to the case.
There is one more possibility, a "cooked" CPU. If the CPU overheated and destroyed itself, it is possible it is causing the power overload. Same goes for the power regulators around the CPU socket, depending on CPU type and motherboard. Many board have bad capacitors around the 3.3V regulators around the CPU area. If those caps are bad (bulging on top), then you need a new motherboard.
 

wayneh

Joined Sep 9, 2010
17,018
If there’s a battery on the board, check the voltage and/or replace it. A failed battery is enough to completely kill booting.
 
Do you have to unplug the power supp;y from the outlet to get it to try again? I have used several old PSUs for bench power supplies and every time I messed up and shorted one of the wires I would always have to unplug from the wall and plug it back in to reset it. I don't know if this is the case with all supplies so maybe useless information, but who knows. It may at least narrow the possibilities a little... the toasted HDD may be the culprit if it's still connected. Otherwise it should give a missing hard drive warning (maybe).
 

Thread Starter

StrongPenguin

Joined Jun 9, 2018
287
Thanks for all the great inputs, everyone! I need to get my captain in on the idea of investigating this machine. He is usually a very good partner in crime.

@SamR From what I can see, based on similar computers onboard, the HDD is SSD, and from where the computer is located, it is difficult to hear anything spinning. The computer is just DOA, nothing comes up.

@sagor If I could get access to measure these voltages, that would be great. I will try starting up with everything disconnected. And check that darn green wire, too.

@geekoftheweek It has a HDD LED on the front, which blinks on working computers but not this one. Does not look good.

@wayneh and @AlbertHall Will hopefully drag the computer up on the bridge for inspection and check those two things.

Many of you suggest the battery. I will try to change that first, and if that does not work, then try to reset the BIOS (if it does not already reset during the change).

But this is a "special" computer. Could I risk not setting the BIOS right again and end up not booting, or some radar software not wanting to play ball?

I will also check the caps, hopefully they are fine.
 

sagor

Joined Mar 10, 2019
394
Removing or changing the button cell battery will not fix any power supply issues. All that does is clear the BIOS settings. If the battery was dead, your BIOS would come up with a message about it, or produce a BIOS error due to lost BIOS settings.
Focus on other issues first....
 

wayneh

Joined Sep 9, 2010
17,018
Removing or changing the button cell battery will not fix any power supply issues. All that does is clear the BIOS settings. If the battery was dead, your BIOS would come up with a message about it, or produce a BIOS error due to lost BIOS settings.
Focus on other issues first....
That's specific to the model of computer, which we have not been told. A dead battery can absolutely brick a computer.
 

Hymie

Joined Mar 30, 2018
962
I had a similar problem a few years ago with an aging PC, despite trying many of the suggested fixes it did not come back to life.
In the end I concluded the most likely issue was the motherboard was shot, and threw it in the bin after removing the hard drive.
 

Thread Starter

StrongPenguin

Joined Jun 9, 2018
287
Great succes today. I am sorry that I can not provide any pictures because of company policy.

The computer is a "special" radar computer from a non standard computer vendor. I can't find any information on the motherboard.

It turned out the PSU which was used to test, was not a proper fit. This original one got a start signal from two points: the motherboard and the reset (or atleast in that area/board) button. The one which was tested against did not have this 4 pin connector going over to the reset button.

So the guys who tested the alternative supply did not connect this second start signal, resulting in the fan only blowing for a second, then shut of.

I backtraced this reset wire and connected it to the motherboard with the help of a little jumper. Viola! Happy penguin.

I also changed the coin battery before all of this and looked for bad caps. I found one right beside a chip I could not identify, because a heatsink was hiding it. I assume it was not the processor, because there was another larger heatsink under the fan, which I guess was the CPU. There was a cap with a small hat, but not enough to kill the computer.

Thanks for all the help:D
 

Danm1

Joined Jul 19, 2010
69
I lot of computer fans start fast then slow down, that might not be the problem.
If there are faults lights on the mother board that might provide some information.
 

ApacheKid

Joined Jan 12, 2015
376
We have an 8 year old PC for a radar, which does not start.

It behaves as though I needs power, because when you power on, the fan starts blowing and stops after a couple of seconds. Then nothing happens after that. Power LED is lit during the whole time.

I know there are sensing lines and OK signals. Is there any way to check if these are good?

We have tried with a different PSU which works, but no luck.

If the HDD is toast, it would not behave like this, no?
Depending on the age of the machine, its motherboard, it could be the "capacitor plague" and thus an easy fix.

I had a PC years back, like thirteen years ago or so and it behaved like yours. Because I knew something about electronics and was fine with soldering I replaced an electrolytic capacitor on the board that looked slightly swollen. Prior to that I'd changed the battery etc to no avail.

The machine worked, booted fine. It was a few weeks later that I then read about this capacitor plague and realized that that's exactly what had happened!

In fact this picture from the Wikipedia article is very similar to what I saw, the cases in my case weren't ruptured but were visibly bulging:

1616167713649.png
 
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