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Help with "Homebuilt"

Posted on 1998-02-19
Medium Priority
Last Modified: 2010-04-12
I'm building my first PC on an Abit AX5 mb ("jumperless") in an ATX case (Elan Vital). (FYI, I'm aware of the rear on/off switch and know how to use it in with the front switch.)

My problem is that since the initial boot, I'm unable to boot it again. (The chassis fan turns over a few times, but that's it.) I've also cleared the CMOS in an attempt to start from scratch. Plus, I've tested the front switch via jumping the power on/off lead on the mother board, and it appears to be good.)

Any suggestions?

Question by:rhyma
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Author Comment

ID: 1129267
Edited text of question
LVL 32

Accepted Solution

jhance earned 400 total points
ID: 1129268
My first suspect here would be the power supply.  You should disconnect the motherboard and all of the disk drives and then see if you fan goes.  If not, then at least your +12V is gone, perhaps the whole thing.  If it does run, there are a couple of possibilities:

1) You have overloaded the power supply with too many devices.  Check the power ratings on the various parts and compare that with the output of the power supply.

2) Your power supply is defective and doesn't operate under load.  In this case, I'd caution you against plugging any of the expensive parts of your system into it until you've debugged it fully.  

BTW, power supplies are usually very poorly made in "Taiwan Brand" cases and having a bad one is not at all unusual.  

Author Comment

ID: 1129269

Thanks for the prompt reply.

I'm sorry I forgot to mention that I already tried a new p/s. The original was 235w and I planned to put in a 250w, so I had it on hand, and neither worked. (FYI, the first was an "SPI" and the second was an "NSpire" ... and it booted once with each.)

Please bear in mind that the first time it booted I was able to enter the setup/bios, etc.

And at this point the cards I have in their are a video card, sound card, and extra parallel port card (for scanner) which I haven't hooked up yet.
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LVL 32

Expert Comment

ID: 1129270
I'm still concerned that your fan isn't running.  Unless the fan itself is just stuck, when it doesn't run, it means that +12V power is not being supplied.  If you are confident that the power supply is OK (and I'd strongly suggest testing it with a VOM or Volt-Ohm Meter for proper output), then something else is "sucking" down the power on one of the outputs so that there isn't enough to power the fan or anything else.  Take it step by step and remove things from the power supply one at a time until you find the culprit.  Don't count out a short from the motherboard to the case or even something as simple as a screw lodged between the MB and the case.

Another thing I've seen many times is using a too long screw to mount a hard drive.  The end of the screw touches or even crunches into the circuit board and shorts it to the case.  Since most hard drive circuit boards have a power plane in the middle, guess what happens?  The +5V gets shorted to the case.  The thing about the switching power supplies used in PCs is that if you short one output, none of the others will work either.


Author Comment

ID: 1129271

I did as you suggested, and the damn thing actually booted. ;-)

FYI, all my peripherals seem to be OK, and the only thing that's different (that I'm aware of) is that I had a "Turbo LED" lead connected to pins 9&10 (Sleep LED), and this time I didn't connect it.

Could that have caused the problem? (It's hard to believe.)

The only problem I have now, that I'm aware of (assuming it boots when I get back to it), is the fact that the floppy drive light stays on. Any idea how to fix it?

And finally, assuming both my power sources are OK, which do you feel I should stick with ... the 235w SPI, or the 250w NSpire? BTW, there's no difference in cost, and the reason I'm asking you is that you seem to know more about p/s than the vendor I purchased it from.

Thanks again for helping me out, I really appreciate it.
LVL 25

Expert Comment

ID: 1129272
Rhyma: On the floppy, reverse the ribbon cable on the drive so that the edge with the red trace is next to the power connector.

On the power supply, go with the 250w! 235's are relegated to desktop non-tower units that won't see much equipment.
LVL 15

Expert Comment

ID: 1129273
ITS AN ATX Power supply!
You CANNOT disconnect it from the motherboard and still have it power up!

the power supply will not provide power to the board unless it recieves a "power good" signal from the motherboard.  It will provide an initial voltage to the board to "test" but then will pull all power if it is not recieved.

Unplug all ribbon cables from the motherboard, pull out all the cards.  Then see if the board will power up (without video card even).

That seems like a good place to start troubleshooting to me..

Author Comment

ID: 1129274


The red stripe was already next to the power connector. But, I'm going to reverse it at the mb connector anyway.

Author Comment

ID: 1129275

Thanks for the good advice.

I did get the system to boot (see my last comment to jhance)doing basically what you and he suggested.

But feel free to answer my final questions ... which he didn't, as of this writing.

Thanks again ... especially for the point about testing the p/s if it's not connected to the mb.
LVL 25

Expert Comment

ID: 1129276
Rhyma, we can't post here now, as it costs points to come back here now that you've accepted an answer. Hopefully everything works!

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