PC Speaker makes terrible hum before POST, then acts normally. \ VOGONS

PC Speaker makes terrible hum before POST, then acts normally.

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First post, by shadmere

Posted on 2020-09-09, 22:23

shadmere Offline

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So I've been working on this 486 for awhile, and just now am ready to close it up.

I also realized, when about to do so, that I never hooked up the PC speaker, reset switch, etc. Weird.

Anyway I hook all that up.

It still works, but now there's a terrible hum when I turn it on. The hum is definitely from the PC speaker (doesn't happen when it's not plugged in). As soon as the computer finishes the memory test, the hum goes away. I get a normal POST beep, and then everything acts normal.

On a previous motherboard that I never was able to get a hard drive working on, the PC speaker did not behave like this.

Is there something I might be able to look for to change about this? I guess I can just ignore it, but the sound makes me think something terrible is happening in there.

Here is a youtube of the noise: https://www.youtube.com/watch?v=F82tzQJUVM4

Edit: I have tried plugging the PC speaker in the other direction, just in case, but no change.

Last edited by shadmere on 2020-09-09, 22:26. Edited 1 time in total.

Reply 1 of 3, by Tiido

Posted on 2020-09-09, 22:25

Tiido Offline

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that's the "memory count tick", there should be a BIOS option to turn it off.

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Reply 2 of 3, by SodaSuccubus

Posted on 2020-09-09, 22:25

SodaSuccubus Offline

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I think thats normal for AMIBIOS boards of that era? I have a PCI-486 with a AMIBIOS like yours and it too produces a near identical buzzing humming noise until the memory test is done

Reply 3 of 3, by shadmere

Posted on 2020-09-09, 22:28

shadmere Offline

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Wow okay.

I had a 486 back then, and knew a couple people who did, but I guess that just wasn't ever enabled. That noise was so terrible I didn't even consider that it might be intentional, and all my Googling just brought up things about ground loops, hah.

That was definitely it. I'm glad one of my problems was so simple for once.

Thank you!

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