Strange Internal PC Speaker Sound

[Flamin Joe]

Hi all,

I've got a strange sound coming out of my Internal PC Speaker on one of my Atari IBM XT clones. I did a short video below which is easier then trying to explain what it sounds like. One thing I noticed too is if you put your ear up really close to the speaker you can hear the sound it is supposed to be making but it is very faint. In this case it's attempting to play a song from Bard's Tale II.

My first thought was perhaps the speaker was faulty but I tried another known working speaker and it was exactly the same. Next I took out all the expansion cards (Sound Blaster, Rampage memory card and VGA adapter) so it was down to the bare minimum with just the RLL Controller card and it made no difference. I know it's not software related either as the same sound occurs during the POST beep.

I tested it with a multimeter while playing sound and it went between 4.4v and 5.0v so it doesn't look as if that is the problem.

Any ideas?

 

[Trixter]

I'm not an expert, but isn't it supposed to go between 0v and 5v? ie. that's how the sound is generated. If it's only going from 4.4v to 5v that would result in the very quiet output you're hearing.

If this were an IBM mobo we could consult specs, but your compatible is likely constructed differently. If you switched out speakers and the behavior still stands, I'm afraid you need to start checking traces and components on the board that involve the speaker.

I've worked with the PC speaker a lot in both clones and the real thing, and unfortunately I've never come across the behavior you're seeing.

 

[Flamin Joe]

I should clarify, when it's playing no sound at all it's at 0v. As for the 4.4v to 5v reading, it could just be a case of my multimeter not displaying the changes quick enough so the 4.4v is just an in between reading as it's dropping to 0v then quickly back to 5v. Only just occurred to me now that could be the case so there might be nothing in it.

Fortunately I do have the schematics for this particular motherboard so I do have something to reference from. I was hoping though that perhaps I was overlooking something and there might be a easier solution to the problem.

 

[Flamin Joe]

I put off looking into this further since I last posted but just recently discovered something after firing up the PC recently and playing around with a few games.

I was playing SimCity and the Hamburg scenario and the explosions and other sound effects sounded exactly as I remembered them which had me puzzled especially since the POST beep was it's normal muzzled self. That got me thinking, what if it's an issue with just high pitched beeps? So I installed and fired up the perfect candidate to test this theory, Alley Cat, as I knew it hard a mixture of high pitched and low pitched beeps during the game. Low and behold confirmed. The high pitched noises, for example when you jumped into a window and it changed screens, were muzzled. The other background noises, jumping, running etc were still all there.

So my question is, what in the PC speaker circuitry would be causing the high pitched beeps to fail but the low tones to play fine?

 

[Osgeld]

fisrt thing that pops to mind is bad capacitor(s)