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Thread: 5160 Boots fine but no beep or PC speaker sound

  1. #1
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    Default 5160 Boots fine but no beep or PC speaker sound

    Greetings!

    Just happened upon this forum after many a Google search on things for my XT.

    Had it for a while (a few years) and haven't done much with it yet. Got my first one in 6th grade back in 89 (My uncle worked for IBM and sent me one hehe.)

    My question is this...

    When I boot up the XT, everything works great(mostly). 640k of RAM tests good, VGA card works fine, 360k floppy is good, 10MB MFM HD boots, though it's on its way out by the sound of it, heh.

    I'm going to eventually "pimp it out", but my main issue is that I get no POST beeps, and none of the games or things that use the PC speaker make any noise.

    How would I go about testing and repairing/replacing it?

    I tried a speaker from an old computer case I had(that works when the other computer boots), and still nothing.

    Thanks in advance!

  2. #2

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    You might have some corrosion or a short on the 5V line before the speaker. Check the traces for cuts or other damage.

  3. #3
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    Quote Originally Posted by Jeri View Post
    Greetings!
    Welcome to these forums.

    Quote Originally Posted by Jeri View Post
    How would I go about testing and repairing/replacing it?
    As a very first thing to look at, verify that the speaker's connector uses the outer pins, per the photo at [here].

    Quote Originally Posted by Jeri View Post
    I tried a speaker from an old computer case I had(that works when the other computer boots), and still nothing.
    And just to be sure, verify operation of the 5160's speaker in the other computer.

    Quote Originally Posted by Jeri View Post
    How would I go about testing and repairing/replacing it?
    Beyond basics, using certain test equipment, we need to start probing various points on the motherboard. Do you have a multimeter, or logic probe, or oscilloscope ?

    And if a faulty component on the motherboard is discovered, do you have the means/skill-set to replace it ?

  4. #4
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    Quote Originally Posted by modem7 View Post
    Welcome to these forums.
    Thank you!

    Quote Originally Posted by modem7 View Post
    As a very first thing to look at, verify that the speaker's connector uses the outer pins, per the photo at [here].
    It does.

    Quote Originally Posted by modem7 View Post
    And just to be sure, verify operation of the 5160's speaker in the other computer.
    I did not think of this. I will check it out.

    Quote Originally Posted by modem7 View Post
    Beyond basics, using certain test equipment, we need to start probing various points on the motherboard. Do you have a multimeter, or logic probe, or oscilloscope ?
    I do have a digital multi-meter that I bought a while ago. It still works, I just have to bring it to my desk (I think it's in the basement. LOL)

    Quote Originally Posted by modem7 View Post
    And if a faulty component on the motherboard is discovered, do you have the means/skill-set to replace it ?
    Yes. My soldering skills are not at the master level or anything, but I did manage to replace 5 faulty resistors in my Buick Century's dash panel to get the odometer working again. (I took 3 years of electronics classes in HS in the mid-90s, and most of it has stuck with me LOL.)

    Thanks for the replies. I'll check for traces and corrosion first (not sure why I didn't already think of that, heh), and let everyone know what I find.

  5. #5
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    Assuming possession of a logic probe or oscilloscope:

    Step 1: Refer to the diagram at [here].

    Step 2: Power up the 5160 to Cassette BASIC. At this point, we know that the POST has already appropriately configured channel 2 of the 8253 chip (channel 2 used in speaker support).

    Step 3: In Cassette BASIC, enter the following command: OUT &H61,INP(&H61) OR 3

    Referring back to the diagram, the command takes the 'Speaker data' and 'Timer 2 gate' lines high.
    On a fully functional 5160 motherboard, a continuous tone will now be heard from the speaker.

    Expected is:
    * 'Speaker data' line will be high.
    * 'Timer 2 gate' line will be high.
    * Pin 18 of the 8253 chip will have a clock signal on it (of about 1.2 MHz).
    * Pin 17 of the 8253 chip will have a square wave on it (of about 988 Hz).
    * Pin 11 of the U87 will have a square wave on it (of about 988 Hz).
    * Pin 6 of U85 will have a square wave on it (of about 988 Hz), but only if a good speaker is connected, because the speaker acts as a pull-up in the circuitry.

  6. #6
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    Additional to my previous post:

    Refer to the diagram at [here].

    Two parts of the speaker circuitry are fed back to the PC4 and PC5 pins of the 8255 chip.

    Therefore, with a continuous tone sent to the speaker, we should be able to see, via BASIC code, pins PC4 and PC5 toggling periodically.
    Note that to see PC4 changing, the speaker needs to be in place (it acts as a pull-up in the circuitry).

    In our code, we first send the continuous tone to the speaker, then we read port C of the 8255 multiple times, expecting to see bits 4 and 5 of port C toggling periodically.

    10 OUT &H61,INP(&H61) OR 3
    20 FOR A = 1 TO 15
    30 PRINT STR$(INP(&H62)) + ", ";
    40 NEXT A

    RUN

    Running the above BASIC program on my fully functional 5160, produces something like "23, 39, 23, 23, 39, 23, 39, 23, 39, 23, 39, 39, 39, 23, 39, ", a pattern of two numbers, 23 and 39.

    23 decimal = 00010111 binary
    39 decimal = 00100111 binary

    So, on my fully functional 5160, I see both bits 4 and 5 toggling, as expected.

  7. #7
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    I removed the MFM controller to get it to boot to BASIC, and input that code.

    I got a pattern of 16 & 48. But no sound from the speaker.

    I did put the speaker in the Pentium II I had on hand, and it played Prince of Persia in DOS through it just fine. Louder than the speaker in the Pentium II's case, in fact. LOL

    So, speaker is good.

  8. #8
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    Fortunately, the circuitry between the timer (creates the beeps) and the speaker is pretty simple. See PDF page 316 (marked D-9) here.

    I've linked to the 16-64K first version of the 5150 motherboard; the same site has the technical data for the 64-256K board as well. With respect to the speaker circuitry, there's no substantial difference.

    The first place that I'd check would be the inputs and outputs of the 75475 driver.

  9. #9
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    Quote Originally Posted by Jeri View Post
    I removed the MFM controller to get it to boot to BASIC, and input that code.
    I got a pattern of 16 & 48. But no sound from the speaker.
    16 = 00010000
    48 = 00110000

    So, bit 5 toggling, but not bit 4. Per my earlier note, you would have had the speaker fitted.

    Referring to the diagram at [here], I see the major possibilities as being:
    * Faulty U29 (not taking the 'speaker data' line high).
    * Faulty U87
    * faulty U85

    The joints on the 5150 motherboards that I have encountered, have been reliable. Where I have seen joint problems is on the connector for the keyboard (stressed each time keyboard added/removed) or when the motherboard has been exposed to a leaking battery.

    Quote Originally Posted by Jeri View Post
    (I took 3 years of electronics classes in HS in the mid-90s, and most of it has stuck with me LOL.)
    Good. You now have enough information to fix the motherboard.

  10. #10
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    Quote Originally Posted by modem7 View Post
    Assuming possession of a logic probe or oscilloscope:

    Step 1: Refer to the diagram at [here].

    Step 2: Power up the 5160 to Cassette BASIC. At this point, we know that the POST has already appropriately configured channel 2 of the 8253 chip (channel 2 used in speaker support).

    Step 3: In Cassette BASIC, enter the following command: OUT &H61,INP(&H61) OR 3

    Referring back to the diagram, the command takes the 'Speaker data' and 'Timer 2 gate' lines high.
    On a fully functional 5160 motherboard, a continuous tone will now be heard from the speaker.

    Expected is:
    * 'Speaker data' line will be high.
    * 'Timer 2 gate' line will be high.
    * Pin 18 of the 8253 chip will have a clock signal on it (of about 1.2 MHz).
    * Pin 17 of the 8253 chip will have a square wave on it (of about 988 Hz).
    * Pin 11 of the U87 will have a square wave on it (of about 988 Hz).
    * Pin 6 of U85 will have a square wave on it (of about 988 Hz), but only if a good speaker is connected, because the speaker acts as a pull-up in the circuitry.
    Quote Originally Posted by modem7 View Post
    16 = 00010000
    48 = 00110000

    So, bit 5 toggling, but not bit 4. Per my earlier note, you would have had the speaker fitted.

    Referring to the diagram at [here], I see the major possibilities as being:
    * Faulty U29 (not taking the 'speaker data' line high).
    * Faulty U87
    * faulty U85

    The joints on the 5150 motherboards that I have encountered, have been reliable. Where I have seen joint problems is on the connector for the keyboard (stressed each time keyboard added/removed) or when the motherboard has been exposed to a leaking battery.


    Good. You now have enough information to fix the motherboard.
    Ok. I managed to get my hands on a logic probe and came to the following conclusions...

    Speaker Data line is High

    Timer 2 gate line is High

    Pin 18 of the 8253 chip will have a clock signal on it (of about 1.2 MHz).
    - Yes

    Pin 17 of the 8253 chip will have a square wave on it (of about 988 Hz).
    - Yes

    Pin 11 of the U87 will have a square wave on it (of about 988 Hz).
    - Yes

    Pin 6 of U85 will have a square wave on it (of about 988 Hz), but only if a good speaker is connected, because the speaker acts as a pull-up in the circuitry.
    No. This pis is constantly HIGH, it does not oscillate, with a speaker connected, and no signal(H or L) without.

    A faulty U85?

    Thanks!

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