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Thread: IBM 5150 Whistling Sound

  1. #1

    Default IBM 5150 Whistling Sound

    A while back I had posted that I have an IBM 5150 which was making a high pitched whine/whistle from its speaker. I thought the problem was a bad/failing power supply but it turns it isn't the PS after all because I sent it off to someone and they said everything tested normal. So now I'm stumped as to what could be causing this. The sound is coming out the speaker (It goes away if I unplug it) but it's not the speaker itself (it works fine for games and music) or any cards in my system as it makes the noise without anything plugged in or hooked up (just power to the MB). Also the sound disappears after the system warms up for 10 min or so which makes me wonder if it's a capacitor on the mother board or something similar. Any ideas?

    Here's a video with the noise: Http://www.atariprotos.com/temp/5150.mov

  2. #2
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    I can barely hear it in your video, but I think it still could be your PSU--it may read fine, but there's noise being coupled into the +5 bus.

    Let's see if we can quiet things down a bit.

    Look at C9--it should be a .01 uF cap. Try paralleling another .01 with it and see if the noise decreases.

    A more extreme thing to try would be to replace U95, but it probably won't do much good.

  3. #3

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    In person it's loud, trust me.

    The guy in this video seems to have exactly the same problem: https://www.youtube.com/watch?v=0_h-NAIxrlk

    So it's either a failing power supply or a bad cap on the MB or both. My problem is that I don't have the tools to test stuff like he did in the video (I have a crappy cheap volt meter and that's it), so diagnosing this is going to be hard.

  4. #4

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    The PSU is easy enough to exclude -- try another one.
    PM me if you're looking for 3" or 5" floppy disks. EMail For everything else, Take Another Step

  5. #5
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    You should also be able to use a cheap and cheerful high impedance crystal earphone. One end on 0V/GND and the other used as a probe.

    U63 pin 13 (OUT 2 from 8253) should have a constant tone on it.

    U63 pin 12 (SPKR DATA) should be normally '0' with no sound and '1' with sound.

    U63 pin 11 should normally be high (+5V) with no sound required and oscillating (as per input pin 13) when input pin 12 is high. Do you see/hear anything strange on this pin?

    U95 is the high current/voltage driver for the speaker.

    +1 for parallelling up a 0.01 uF capactitor across C9 (this may have gone open circuit - so the simplest way of testing is to substitute with another known good capacitor in parallel).

    After that - PSU ripple...

    Dave

  6. #6

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    Quote Originally Posted by Stone View Post
    The PSU is easy enough to exclude -- try another one.
    If I had one.

  7. #7

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    Quote Originally Posted by Chuck(G) View Post
    I can barely hear it in your video, but I think it still could be your PSU--it may read fine, but there's noise being coupled into the +5 bus.

    Let's see if we can quiet things down a bit.

    Look at C9--it should be a .01 uF cap. Try paralleling another .01 with it and see if the noise decreases.

    A more extreme thing to try would be to replace U95, but it probably won't do much good.
    I think I'm going to have someone replace all the caps on the +5V line and see if that fixes things. I also have someone who is going to loan me their XT power supply so I can see if it's the power supply.

  8. #8

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    It doesn't need to be from an XT. Any PSU with P8, P9 connectors will work.
    PM me if you're looking for 3" or 5" floppy disks. EMail For everything else, Take Another Step

  9. #9

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    Quote Originally Posted by Stone View Post
    It doesn't need to be from an XT. Any PSU with P8, P9 connectors will work.
    Really? Hmm... I'll have to take a look around my room and see what I might have. Any likely candidates I should check?

  10. #10

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    XTs, ATs, 286, 386, and 486 clones.

    I even have a 586 with dual power connectors... both AT and ATX.
    PM me if you're looking for 3" or 5" floppy disks. EMail For everything else, Take Another Step

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