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Vm Audio Surround Sound

Discussion in 'Troubleshooting and Repair' started by Michaelf30, Dec 23, 2016.

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  1. Michaelf30


    Dec 23, 2016
    I have a vm audio exms581 surround sound system. It has worked fine for the first couple of years but now something is wrong with the volume. No matter what input I put it on or device I use I can barely hear it out of the speakers even at full volume. I opened it up to look for a blown capacitor or burnt spot but didn't see any. Any advice would be appreciated thanks.

    Attached Files:

  2. 73's de Edd

    73's de Edd

    Aug 21, 2015
    Sir Michaelf30 . . . . . . .

    Looks like you got about 4 years of use of this unit.

    Somewhere between absolutely nothing and nil is being available for any service info from this units
    designated Shindigen manufacturer.
    They second source to multi distributors / brands . . . thats even including Wally World.
    They want to Sellee Sellee . . . . . . . . . . . but alas . . . . . .no want you to Fixee Fixee.

    What my Sharp Eagle Beagle eyes are seeing, would be two warmed ? up spots on the board at the
    inclusively marked up RED RECTANGLES.
    Nothing thermally relevant is being seen on this side of the board, is there a possibility that hot components
    are mounted at those spots on the other side of the board ?

    At the extreme left of the board are lined up all of the U1 through U7 POWER OUTPUT INTEGRATED CIRCUITS
    MODULES for the five POWER AUDIO output portions of this unit.

    The YELLOW STAR marked units are probably being related to feeding the rear spatial speakers.
    Can you pass on to us, their identification markings, placed on the sides of their cases.

    The FUCHSIA STAR marked units seem to be receiving a bit of a differrent treatment, in respect to their
    adjunct ancillary electrolytic capacitors.
    Therefore, can you release the compressive bar with the GRAY RECTANGLE marked screws , to expose
    those power unts identifications and pass back those to us also.

    Just for information, the two ORANGE RECTANGULAR marked up areas are the +27 and -27 Volt power
    supplies for all of those power amps.

    Drop down to the top two BLUE RECTANGLE markups and you have the basic power supply for the bulk of the rest of the unit.
    One supply line then drops down and then feeds into the top lead of that YELLOW RECTANGLE with its burnt 4.7 / or /.47 ohm resistor that has its bottom lead going down into the BLUE BOXED heatsinked regulator area.

    Pass that heat sink mounted parts ID on to us also.

    My RED STAR marked boxes at the very bottom must just be enclosing hidden / recessed input and output connections .

    Initial metering will be done by having the set UNPOWERED and use of a DVM set in its ohms mode and set to its lowest ohms range and shorting the meter leads together to initially confirm your familiarity between a shorted connection . .which your meter will then display.
    Then open the leads to confirm a non connective meter reading.

    Then take the test leads and test across the 4 top fuses to confirm connected . . .intact . . .internal fuse links.
    I feel sure that all 4 will be testing good.

    Further info to be collected, would now require the use of a DVM in its AC mode and the unit powered up, in
    order to get your weakened sound and then start at the very top right connector with its 5 connections of.
    Meter common negative goes to the center black connection and then meter between the two YELLOWs for their A.C. voltages and then the bottom two BLUES, with all of those voltages then being passed on to us.

    Then go to the *yellowed* connector, just below, and use its top gnd connection to your meter black lead and
    check for those marked voltages of 27 and 4 and 4. Expecting the 27 to be correct and DC, but that marked up two 4 Vs could be an AC voltage or possibly also AC if you change to metering only between the bottom 2 connections..

    Drop down to the 3rd connector and go to AC metering mode and see if the meter Black is placed on one of the two black wires, that the two BLUE wire above, will show AC voltages being present.
    Then at the 2 pin connector below I believe that meter probes can reach into half of the connectors 2 RED wire connections to acquire a final AC voltage across those two wires.Pass on that voltage.

    Final reading will be between the cluster of 4 diodes just beside the last RED wire set tested . .ignoring the slightly spaced apart, sole diode, at their very top.

    Use DC voltage test mode this time and use the LEFT side leads of either of the 3rd or 4th diodes up for being your your negative-black metering lead common and use the RED metering lead to test the voltage on the top of the earlier mentioned burnt resistor [ YELLOW BOX ]. Log down Voltage reading.
    Then move the meter lead to the bottom lead of that resistor to see what voltage is getting through . . . . . . .if any.

    Thasssssit . . . .now its doittoit . . .time.



    73's de Edd
    Last edited by a moderator: Dec 29, 2016
    Michaelf30 likes this.
  3. Michaelf30


    Dec 23, 2016
    t doesn't look like anything on the other side caused the brown spots I will upload a picture of the other side.

    The Yellow Star components are boomtech tda2030a.
    The Fuchsia Star components I could not get two of the screws out so I can't tell you what they are.
    The heat sink mounted device was also too difficult to see.
    The left red star is the output to the 5 speakers and the right 2 are 2 inputs.

    I did a continuity test on the fuses and they were ok.
    1st connector

    The two yellow connectors are 17V.
    The two blue connectors are 14V.

    2nd connector

    The D27 connection shows -25.6V.
    The two A4s show 2.8V

    3rd connector

    A4 2.8V
    A4 2.8V
    A27 29.5V

    Bottom 2 red. one probe on first red second probe on other red 12.2V

    Diode to top Resistor voltage 14.8V
    Diode to bottom Resistor voltage 14.8V
    Hope I got all the voltages tested correctly thanks for the help.

    Attached Files:

    Last edited by a moderator: Dec 29, 2016
  4. 73's de Edd

    73's de Edd

    Aug 21, 2015
    Sir Michaelf30 . . . . . . .

    In an examination of the foli side of the PCB it is now readily evident that the central discolorato of the PCB as being from time related heating of the board from The RED rectangle and STARRED power semiconductor mounted there.
    Looking at the right half of the board I have drawn in the sub power supply foils that carry down the 12VDC and the ground buss.
    They end up at either a power semiconductor or MOST likely, a 3 terminal regulator. Which you say that you cannot read its part number.

    See if you can make yourself a mylar foil mirror.
    You explore all of your foil sealed junk food container bags and very likely you will find one that they are using silvered mylar film that is almost optical quality on one side and the other, not quite up to that clarity. Test it pressed up next to, and right against some printing.
    Get your self a backer board of very- very thin plastic or a playing card thickness and cut it out to a square ended manicure / emory board dimensioned backer .

    Cement the dullest side of the mylar film to that backer using white glue, rubber cement, non acetic acid bearing silicone rubber adhesive / sealant or double sided tape.
    No Duco / model cements or Super glues . . . as their applied chemical mixes and adjunct fuming will destroy the silvering.
    Then . . . . in conjunction with a companion BRIGHT light . . . . you will have yourself an optical mirror for using in VERY micro confines, that will make a common dental inspection mirror look like an elephant in the room.

    On your getting the heat sink clamp bar off. Probably due to trying to use a common Phillips tip instead of the metric ISO tip that those screw heads require to REALLY seat down FIRMLY within the head.
    I 'll just bet that a set of Vise Grips with their milled grooves set at a 90 degree to the screw head and a 1/4 turn will then initially break loose the tight screw, such that the screwdriver can then be used.

    Getting back to the suspicioned 3 terminal regulator . . . . which is now being marked up as a PINK rectangle.

    DC voltage meter its 3 leads and sort of expect the given 12VDC being on one terminal, the other terminal to be grounded and then the final output terminal to be at 12VDC or other possible lower options of 9, 8,6 or 5VDC.
    I was certainly expecting that heated resistor to be open circuit.

    Testee . . .testee . . . .



    73's de Edd
    Last edited by a moderator: Jan 4, 2017
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