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#5 WPC DCS Sound PCB (Roadshow)

Discussion in 'The Menace Files' started by Menace, Jun 18, 2013.

  1. Menace

    Menace Well-Known Member
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    Alright, literally just finished this repair and thought I'd post it up because well... it turned out to be simple, which means a nice short write up.

    20130618_003528.jpg

    This PCB came to me from one of our PBREV members a few weeks ago, but given my back-log among other things I just didn't have the time to put this on the bench. The owner had given me a brief rundown of what the issue was, very loud buzz and the volume controls in the game had zero effect on the level. For some reason I want to say the owner also mentioned there was no game sound as well, which initially had me thinking this was a DSP issue. (DCS games have the volume control integrated and controlled by the DSP where pre-DCS games actually used a Z-pot or electronic potentiometer for this task)

    First things first, I toss the PCB into my Shadow for the initial symptoms test and fire the game up and just about soiled myself as the loud buzzing started immediately and caught me off guard! Once I composed myself I immediately reached for the volume controls and started to adjust the game volume, and that's when I could just barely hear the Roadshow background music under the buzzing. This my friends is a GOOD thing, because it confirms that in essence the sound board is actually working as it should, just with a real nasty ground buzz drowning everything out.

    Now I just happen to have over 20 years experience in the pro-audio field on top of my electronics background, and when you do enough work in the audio game you encounter a number of "gremlins" along the way, and I knew that the ground buzz I was hearing was definitely a classic 60hz A/C ground buzz. One of the components commonly used to eliminate noise (in this case A/C ripple) from a circuit are capacitors. My deduction at this point was something to do with the filter caps in the power supply section of the PCB, most likely the two large electrolytics in the lower left corner in the above pic - C20 & C21 had either gone bad or something was up with the traces. Grab my trusty WPC schematics and verify the connection points for C20 & C21....

    20130618_003557.jpg

    Now there really isn't a way to test caps with a DMM unless it has a capacitance meter function (which mine does not), but before I pull them I can quickly ring out the traces to and from each cap just to make sure these are in tact. (when I got the PCB someone had touched these up but the caps had never been replaced as they were originals from WMS) DMM in diode/beep setting and the first thing I check are the 2 traces from ground to each cap, and this is when I notice something was up. From ground to the negative lead of C21 it rang out fine (zero's on the DMM and a constant beep), but from ground to the positive lead of C20 it did not. I then rang out the other lead from each cap to the associated diodes and they were all good. So just to verify I tried to ring out the positive lead on C20 to the negative lead on C21 as according to the schematic these are tied together via ground, and again the DMM didn't beep and you can see the floating number value in the pic where it should be zero.

    20130618_004003.jpg


    This confirmed there was a broken ground trace to the positive lead on C20, and I would have to add a jumper to repair.

    20130618_005257.jpg

    With the jumper in place the positive lead to C20 was now ringing out as it should to ground, which meant it was time to toss it back into my game for testing. As I suspected... no more ground buzz, and the sweet sweet sounds of Roadshow were now pouring out of my Shadow. Huzzah!

    So, if there is one thing I cannot stress enough... before ripping into a PCB remember to keep it simple, and check all of the easy things first! (oh and that schematics will always be your best friend) :cool:

    D
     
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    Last edited: Mar 18, 2015
  2. jooky

    jooky Member

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    Thanks so much Doug! I would have never figured that out on my own! That buzz was absolutely UNREAL how loud it was! Can't wait to get it back and start the rest of the troubleshooting and teardown! Much appreciated.
     
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  3. jrholl

    jrholl New Member

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    Hello Doug,

    I know you posted this about a year ago, but I am having the same problems. I also found a floating analog ground problem at the c20 and c21 junctions. I made a new trace using solid 20 AWG wire, and the horrible buzzing sound went away. Yea!! However, there are other problems with the board. All the sounds are being played correctly, but the volume is VERY low, and sometime jumps to full volume (crazy loud). Volume controls dont seem to make a difference, and the sounds seems to be of poor quality.

    Do you have any other suggestions?

    I am considering replacing c32 and c41 as well as the A to D chip (AD1851).

    Many thanks,

    Jonathan
     
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