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Outboard Gear Ashley 31 band EQ troubleshooting - electronics

Discussion in 'Sound, Music, and Intercom' started by mnfreelancer, Oct 25, 2008.

  1. mnfreelancer

    mnfreelancer Active Member

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    Hey guys and gals,
    I do electronics repairs for the company I work for in addition to being a show and events tech, and am having a problem with an Ashley EQ and wanted to bounce the issue off of some of you techs that have bench diagnostics experience...

    It is an Ashley two-channel rack mount 31 band EQ. Inside of the box is four boards total that interface each other on ribbon cables. There are two boards mounted to the back panel and two boards mounted to the front. The rear boards are I/O boards, and the power supply is built onto the Ch2 lower rear board. The front boards have the actual slide potentiometers and likely do all of the actual processing. The problem I'm facing is that both channels have an intermittent self noise that is very distracting, both when hooked up balanced and unbalanced. I say intermittent because it will test fine in the shop, even after many hours of use, but once it's taken to a customer site it will act up again. Granted I have been able to make it act up in the shop but it comes and goes, and not on any definite time interval. Channel one is better than channel 2, as ch2 is almost unusable with how much noise it imparts. It's a very smooth white noise sounding sound that doesn't vary much. An increase of EQ gain increases volume of self noise.

    The bad news is that this EQ has been dropped repeatedly - I keep telling some of the techs I have to work with that dropping gear is bad but to no avail...anyway once when the unit was dropped I opened it up and both of the ribbon cables connecting the I/O to the front boards had dislodged along with the safety fuse. Reconnected everything and found the self noise. Also when I tore the unit completely apart once I found a structural solder trace that helps hold the part of the board where the slide pots are to the processor part (perpendicularly) had broken and pulled its trace off of the board. It does not, however, appear to be electronically relevant and does not have continuity to either ground or hot rails (on either end of the joint).

    Any ideas as to what specific component this problem could be attributed to? My theory is that it has to be something in the power supply, since it is the only thing that relates the two channels together or it is an identical problem with an identical component common to both channels, that would have sustained damage during the same event. Thanks.
     
  2. avkid

    avkid Not a New User Fight Leukemia

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    Have you tried bypassing the internal power supply and using a bench power supply to test?
     
  3. mbenonis

    mbenonis Wireless Guy Administrator

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    I would give Ashly a call. I remember them being very friendly and helpful - they might have some ideas on where to start troubleshooting the device.
     
  4. mnfreelancer

    mnfreelancer Active Member

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    I'd love to but I don't have access to a good regulated power supply...sad I know but I'm the first person to ever work there with a clue about electronics at a component level...I'm workin on getting some more tools and test equipment however.
     
  5. TimMiller

    TimMiller Well-Known Member

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    I bought a really nice tekpower (regulated power supply made by tektronix) new on e-bay a while back for not a whole lot of money, i think around 200. It is programmable through the front panel and USB. It also will log everything such as varying loads in a chart on the computer which aids in troubleshooting random problems. It will output 0-36V and 0-3 amps, so it covers most gear.
     
  6. Chris15

    Chris15 CBMod CB Mods Premium Member

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    Err, Tim, most analog gear would need a split supply to run op amps, from the description you've just given, this supply would not seem terribly conducive to that... This would be a factor worth considering were anyone buying a power supply...
     
  7. TimMiller

    TimMiller Well-Known Member

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    I also have a BK Precision 1760 triple output Power supply. I didn't think about needing a split power supply but that is true. I have thought about one day just using several tekpower supplies instead of a triple output power supply. Power supply's also work well when testing fans to make sure they are running properly, as far as if they are drawing the rated amount of current or if they are putting an excessive load on the power supply.
     
  8. TimmyP1955

    TimmyP1955 Active Member

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    Common power supply problems would be bad solder joints on:

    The PCB mounted power transformer (if applicable).

    PCB mounted filter caps (applicable on most things).

    The power supply regulators.
     
  9. FMEng

    FMEng Well-Known Member Fight Leukemia

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    The most common electronic (non-mechanical) failure in older equipment is dried out electrolytic capacitors. It happens most often in power supply filter applications because heat is a big factor in the life span of electrolytics. The capacitors near hot transformers and heat sinks are most vulnerable.

    I suspect the source of your noise is a regulator oscillating because the bypass capacitors on the output leads are gone.

    The easiest and fastest thing to do is to replace all of the electrolytics in the power supply section.

    This is why keeping an empty space above and below warm running equipment, in your rack, is important.
     

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