(Topic ID: 292275)

Sound out on WPC Twilight Zone

By FathomPin

3 years ago

Topic Stats

  • 4 posts
  • 2 Pinsiders participating
  • Latest reply 3 years ago by WH20_Buzz
  • Topic is favorited by 1 Pinsider


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    #1 3 years ago

    No sound (volume, speaker pins* and audio fuses checked), no hint of any audio noise. Awhile back I started getting a loud audio squawk when the pin was initially powered up, but I thought nothing of it since it was similar to what was common on some WPCs when powered down. Now months later all at once there is no sound at all. I am not sure where to start my diagnosis (audio problems don't seem to be very common on WPC pins and I had never heard that the shock wave to the audio amp I am hearing was so loud it could damage anything), so I am asking for any suggestions to no sound? **My Pinside search skills are not that great, I only saw a thread on replacing capacitors, but my feeling is that sudden failure of a WPC pin with decent audio would not be capacitors (depending on what the capacitors are used for), and is related to the audio board, probably the analog amps.

    *edit to add that I did not check for a broken speaker wire, I initially only checked that connectors 505 and 504 were inserted solid (speaker pins). I read later that the three speakers are connected in series, so a broken wire anywhere between the speakers kills all sound. This is obvious from the fact that only two wires are involved in connectors 505 and 504, but I did not realize to check for broken wires along the chain.
    **BTW, I found this additional info from a Google search that gave me good references to Pinside forum topics that seemed to be better targeted for my needs than Pinside's forum search tool.

    #2 3 years ago

    Most probably U1 on the Sound Board. Measure your speaker Resistance between the wires coming for J504 & J505 on the Audio Board
    If the +25 VDC an -25 VDC is all good and your speakers are not open or short circuit then U1 is most likely.

    Look for signs of burnt components like Tantalum Capacitors going short circuit

    #3 3 years ago
    Quoted from WH20_Buzz:

    Most probably U1 on the Sound Board.

    Thanks U1 was it. I looked at the sound board schematics for U1 in order to sort out the circuit; checked the +/- voltages on U1 pins #3 & #5 (good) then checked the sound board for low voltage audio input into U1 by tapping onto U1 leads #1 & #2 and listening for a signal using earbuds. Now I just need to go downtown and get a new LM1875 IC from our local good-old boy electronics shop that I need to frequent more often anyhow.

    #4 3 years ago

    If you play the Machine with volume over 15 then I would get more than one of them. I measured the Temp on the heat sink once it was 85 degree celcius.
    I'm surprised they don't fail more often


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