Question Why would a motherboard only boot when speaker pins shorted?

May 3, 2020
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I have just fixed a computer by updating the BIOS - nothing out of the ordinary.

However before I updated the BIOS, the only way I could get it to boot was by shorting pins 1 and 2 on the motherboard's speaker.

It sounds crazy and that's why I want to know if anyone has any idea why this sort of thing might happen.
I have inspected the board and there is no visible damage to any capacitors, tracks, etc.

The diagram for the motherboard can be found here: View: https://imgur.com/a/werh10A


Look forward to hearing responses, cheers.
 

Grobe

Distinguished
Are you completely sure you:
  • got the pins correct (maybe you've mistaken speaker pins to be actual pwr pins?)
  • got the correct manual to the actual mainboard model (but pin names on front panel connector should be standardized).
 
May 3, 2020
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Are you completely sure you:
  • got the pins correct (maybe you've mistaken speaker pins to be actual pwr pins?)
  • got the correct manual to the actual mainboard model (but pin names on front panel connector should be standardized).
I'm 100% sure.
See the pins highlighted and a picture I took when I'd just got it including the model of the motherboard (don't want to get it back out of the case now): View: https://imgur.com/a/M6is3WT
 
I have just fixed a computer by updating the BIOS - nothing out of the ordinary.

However before I updated the BIOS, the only way I could get it to boot was by shorting pins 1 and 2 on the motherboard's speaker.
...
Not only is it perplexing why that works, but equally perplexing to me is what possessed you to even try it!

Other than that...if it works don't knock it. I guess.
 
May 3, 2020
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Not only is it perplexing why that works, but equally perplexing to me is what possessed you to even try it!

Other than that...if it works don't knock it. I guess.
What led me to 'try it' was actually an accident.
As you can see there is no speaker unit attached to the mobo and as a last ditch effort (even though I was pretty sure the board wasn't even getting as far as trying to POST) I used a multimeter to try and read the speaker pins to see if it was trying to beep. When doing this I accidentally shorted the two pins using one of the multimeter probes. Didn't even realise that's what I did at first but eventually figured it out.

I just really want to know why this would do anything, I hate not having an answer lol.
 
What led me to 'try it' was actually an accident.
As you can see there is no speaker unit attached to the mobo and as a last ditch effort (even though I was pretty sure the board wasn't even getting as far as trying to POST) I used a multimeter to try and read the speaker pins to see if it was trying to beep. When doing this I accidentally shorted the two pins using one of the multimeter probes. Didn't even realise that's what I did at first but eventually figured it out.

I just really want to know why this would do anything, I hate not having an answer lol.
Well, it's nice to know some accidents work out for the better.

But adding to the mystery...looking at the cheap PC system speakers that come with the 4-pin connector attached the only contacts wired are the two outboard contacts. I have never seen one with the two inboard contacts wired. I always took that to mean the two inboard pins on motherboards would be unconnected too. But in your case it had an effect, so it seems obvious that's not true.

Now the question that comes to my mind: might the two inboard pins have another function? one that factory techs might appreciate but never makes it into user manuals?
 
May 3, 2020
4
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10
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Well, it's nice to know some accidents work out for the better.

But adding to the mystery...looking at the cheap PC system speakers that come with the 4-pin connector attached the only contacts wired are the two outboard contacts. I have never seen one with the two inboard contacts wired. I always took that to mean the two inboard pins on motherboards would be unconnected too. But in your case it had an effect, so it seems obvious that's not true.

Now the question that comes to my mind: might the two inboard pins have another function? one that factory techs might appreciate but never makes it into user manuals?
Perplexing... unless anyone on here has an answer, I'll continue to ask around where I can.
Just as a note, I've given the PC back now after repairing it so I no longer have access to the parts to test any theories.
 

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