PCB Fried! Picture attached and need advice on parts...

Discussion in 'General Electronics Chat' started by Scott_David, Jun 17, 2010.

  1. Scott_David

    Thread Starter New Member

    Jun 17, 2010
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    Hello,

    This PCB is from a KORG KM-402 DJ Mixer. I am having issues with the sound output. One Left channel is dead. Now, you can see where the little transistors or resistors blew off to, I soldered them back in and tested the equip. No success.

    I want to replace these little parts and see what happens. I need resources for suppliers.. Thanks!! Sorry so short!


    http://img638.imageshack.us/i/dsc00875d.jpg/] # 297, 298 and 335.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    IC47 looks bubbly.

    If things blew off the board, they did so for a reason.

    You need to take better photos of the board, and you need to upload them to this site. Use the "Go Advanced" button at the bottom, and then "Manage Attachments" to upload them from your computer. I don't like to go to other sites.

    Photography tips: it's very difficult to take good photos of a circuit board. The best lighting that an amateur photographer can get is outside on a cloudy day in the open.

    If it's a clear day, then drape a clean white bed sheet over the top of you and your subject (use a chair or something to hold it off the ground) and get as close as you can to it with it still being in good focus.

    If your camera has a "macro" function, use it at the largest possible F-stop.

    Indoor flash photos are the worst. The image will be extremely harsh and contrasty, and it will be impossible to make out any significant details. This will only hamper those who wish to help you.

    Since it's dark where I am, you could start off by marking up your image as to which items you soldered back in, and noting whatever markings that are remaining on them, and the associated reference identifiers (like IC47 that I mentioned in my first sentence fragment).

    Always use reference identifiers along with the other numbers that you find on your ICs. This takes a little extra effort on your part, but will help a great deal to get you answers more quickly.
     
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  3. Scott_David

    Thread Starter New Member

    Jun 17, 2010
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    Thanks for the info. The lighting was pretty horrible but I just needed to show the absence of the components "297, 298" that blew off and "335" is turned upside down. Regarding "IC47" it looks like it had residue from an insulated covering that layed on the board...It doesn't look melted, etc but the only way is to test it.

    I circled areas that are missing the transistors/resistors. in the circled area you can see where the parts that flew off reconnected to a solder blob. They are square/rectangle black and red, depending on which side up they are.

    I did not take photos of soldering the parts back in though.

    Thanks for your advice! :D
     
  4. Scott_David

    Thread Starter New Member

    Jun 17, 2010
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    I found what I may need. Ordering the exact part and getting it shipped is another story. I google searched PCB R297 and I came up with th ebuild schematic for a similar mixer. Wiring schematic, circuit schematic, and part description and numbers. Unbelievable.

    Im going to try and contact the manufacturer or try to find a source for these resistors. :) I'll keep this post updated.
     
  5. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,733
    759
    looks to me that they are muting circuitry that got fried....

    and the IC's are preamps..or op amps

    What does the schema says?
     
  6. Scott_David

    Thread Starter New Member

    Jun 17, 2010
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    Here is a description and part numbers of the two that I soldered back on the board. I take it that these resistors are open circuit huh.
    R297-"Carbon Film Resistor(2.2k ohm, 1/6W, J, T-26)" PART # "412-3113-048"
    R298-"Carbon Film Resistor(2.2k ohm, 1/6W, J, T-26)" PART # "412-3113-048"
     
    Last edited: Jun 17, 2010
  7. Scott_David

    Thread Starter New Member

    Jun 17, 2010
    23
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    I can read wiring schematics for rovers and jags but I can't understand PCB schematics too well.

    It pretty much has a flow from one connector to another connector after it filters through a bunch of resistors and transistors and some other symbols I do not recognize.

    I found a few sources for supplying resistors. wish me luck!
     
  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    759
    Good luck then...break a leg.
     
  9. Scott_David

    Thread Starter New Member

    Jun 17, 2010
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  10. Scott_David

    Thread Starter New Member

    Jun 17, 2010
    23
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    Update:
    I installed 4 2.2ohm resistors on my pcb. Everything is working perfectly now.

    I had more than just blown resistors off the PCB. I use turn tables and my needle cartridges that attach to the tone arm were not making good contact. The 4 copper contacts are clean so I placed a small dab of di electric grease to the four contacts on the needle cartridges. My sound issue is resolved.

    As far as the blown resistors I am not sure what circuit/channel they are on. I would only be assuming where they go.

    I'm going to have a fun weekend playing with my new toys finally!! :)

    Have a fun weekend everyone.
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    Glad you got it working again. :)

    If you have copper or brass contacts that are corroded, dunking them in muriatic acid (available at pool supply stores) for about 20-30 seconds and then rinsing them with lots of clean water will remove the corrosion. Don't try this on insulated or stranded wire, as the acid will "wick" up underneath the insulation and eat the wire from the inside.

    That tip came from Kirby Palm's "Experience in a Book" on maintaining Jaguars; the book is oriented towards the XJ-S model, but well worth a read.
    If you google "Experience in a Book" (with quotes) you'll find the PDF.
     
  12. Scott_David

    Thread Starter New Member

    Jun 17, 2010
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    SgtWookie,

    Thanks for the tip. What a coincidence, I work on Jaguars and Rovers. :)

    I use to work on older Jags in San Diego like 80's and a few E-types but nothing to intense like engine rebuilds, etc...

    I will definitely check out that book for resources!

    As far as the contacts, the tone arm has the contacts sunk in a bore about 5-6mm in diameter and about 7-8 mm deep. They look immaculate but Ill use that acid on a Q-Tip and just dab the contacts.
     
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