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General Troubleshooting

swebb asked
Medium Priority
Last Modified: 2010-04-26
I have an old 486 system.  When turning on the power nothing happens.
I don't get any beeps or nothing on the screen.  I have reseated the memory and
video card.  Don't quite know where else to look.  After reading several books on
PC troubleshooting the only things I've come up with are (1) could be a bad power supply,
(2) memory, or (3) video card.  I've ruled out the video card and replaced the memory.  How
do I determine just exactly what is going on?
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OK...lets walk through this....did you add any new hardware when the problem first began...did you do anything out of the norm?
You can try totally disconnecting everything from the motherboard and try booting up then...you should be able to come up and get "invalid system disk" or "missing operating system"
If the system comes up w/out anything connected....replace each piece one by one to see what is causing the problem...lemme know...

You said:  "I don't get any beeps or nothing on the screen."

1) Do you hear power supply fan or drives spin up?  Keyboard LEDs flash?

2) If no, all adapters from motherboard leaving only power supply connector, minimum RAM, speaker, and video card.

3) Disconnect data cables and power supply connectors from all drives & accessories.

4) Re-start computer with keyboard & monitor connected and turned on.



Sorry, it should say:

2) If no, REMOVE all adpters.......


No didn't add any new hardware.  Did nothing out of the norm.  Just turned system on. Disconnected everything (all data cables and power supplies) for all drives.  Restarted the computer.  Nothing.  No beeps, no keyboard leds.  Removed all adapters (only one other adapter and that was network card).  Rebooted.  Nothing happened.  No beeps, nothing on monitor.  Can hear the drives spinning up.

Can you get a known good power supply and try that?  

Can you substitute another motherboard?  Power supply?


If you hear the drives spin up, I'd say the power supply is probably working. (Notice, I said "probably")

Remove the video card & keyboard.
If you get beeps, try another card or k/b.

If nothing, then I'd suggest you find another motherboard.

Now, this isn't very scientific, but the odds are that this will find the bad component.

Let me know if you need more.

Just because the hard drives spin, it doesn't guarantee that the power supply is good.  Try a known good power supply.  Before you try another power supply, try this:  unplug the power to the floppy drive, turn the system on, and see if anything happens.  If the system starts to boot, shut it down, and reconnect the power to the floppy drive (be sure to get it on right!)  Now it should boot normally.  If that doesn't work, try another power supply.  Also, I noticed you said you "ruled out" the video card...what do you mean?  


Tried video card in another system.  Works okay.

"Just because the hard drives spin, it doesn't guarantee that the power supply is good."

C'mon now, I DID qualify my last suggestions based on inability to substitute parts.

I think we have the drives disconnected.

What good is trying a floppy drive test going to do if we can't get the BIOS to self test?


Go here for a pin-out and test the power supply leads with a volt-meter, if you have access to one:


Let me know what you find.

All of the above are more or less correct. BUT, as you hear no sound the three items
that cause the problem are (in order of propability)
1. CPU
2. Motherboard
3. Power supply.

The best way to check it out is to plug in the same components from a friend's system.
For cpu and power supply it 's relatively easy......

Check your little itty bitty tinny speaker connection.  If you've been in there removing cards, it's easy to lift off the tiny two wire connector, then you get no beeps from bios on startup when the system tries to complain.  It's always handy to have a test bed around to check components (another system).  An old 386/486 must be lying around somewhere to use.

generally, if you are methodical and check each component by placing it in a working system, and check your connections carefully (and you might also clean off your connectors, the eraser on a #2 pencil will clean off corrosion) , you will find the failing components.  Of course, you'll probably spend more time in man hours than the system is worth, but what do we have hobbies for anyway, but to spend time and money for our own amusement.

 Also, is this your old 486 system, or another that you have unknown history on?  I've known of amatuers connecting the power supply cables to the motherboard in the wrong order, and blowing out the MB.  They may be still reversed.  That's another benefit to haveing a working system around and open.  If you're not sure how something goes together, you have a reference system to check against.
joopvnetwork specialist

Maybe you swapped the reset switch connector with one of the leds, of keyboard lock connector, or speaker connector.

If the reset switch connector is constantly short-circuited because of wrong connection, the system won't boot up.
And if everything is correctly connected, check the reset switch itself.  These things are sometimes of a terrible quality...


Thanks for all of the advice on this system.  I checked the power supply with a volt meter.  The power supply works fine.  This is not my system.  It is a hand-me-down from one of my other users.  I have no history on this system.  I will continue to check the other things that were suggested.  I'll let you know.

I suspect the Bios is the culprit try to obtain one from some similar pc and check
if it works

let me know

Don't take this lightly, but your computer may have died, literally.  Is it a PS/2?  My borther had one and his just stopped working all of the sudden, no reason at all (except for age).  Also, is there a fuse, or is it not THAT old?  That may pertain to a keyboard problem...

You may try finding a P.O.S.T.-checkcard this displays the codes of the various stages of the startup-proces of the computer, if an internal databus-error accurs or something, the system wil halt before you see anything happen.

this Power On Systems Test will read a specific adres where every test places a code when it starts and when it stops. If a test fails the code of the start of the test is placed in the display of the P.O.S.T card and you can check from a list from you BIOS manufacturer what test the code stands for, so you can start to look

Be certain that the CPU is positioned correctly in its socket. (if it has one)


I have had systems that would not do a thing until I unplugged the floppy drive power and started it, then it would boot.  After doing that once, it would boot with the floppy drive power connected.  I spent a year building systems for a manufacturer/wholesaler, and this would come up every so often, so I'm speaking from personal experience.  Whether or not this is the case here, I know that sometimes power supplies will spin the drives, but the system will not boot.  

I'm not meaning to be argumentative, but read what I said in a comment prior to yours:

"2) If no, all adapters from motherboard leaving only power supply connector, minimum RAM, speaker, and video card."

Any progress yet, swebb?

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No progress yet.  Will check the speaker connection.  However I believe everything is connected okay.  I did find out that someone else had been inside the system before I got to it.  No telling what might have been done to it.  Will keep pushing.
Check for broken connection on mainboard.  I once had a power regulator (3 pin device with one leg broken (1mm)) and computer stopped working until I resoldered it.

Well, I haven't seen this suggestion in any comments, so you may want to check...  From the power supply, there should be 2 clips that you plug into the mother board...  Each connecter, (running straight from the power supply to the motherboard) should have 5 or 6 wires running to the clips.  Check that there 2 black wires side by side (one from each clip) where the power hooks up to the motherboard...        Jade


Thanks for all the suggestions.  I am still working the problem however
because of my time schedule I've had to put it off.  Will continue to work.

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