No power to DJ Mixer - Possible blown SMD fuse?

Discussion in 'General Electronics Chat' started by mynamesalex, Dec 22, 2013.

  1. mynamesalex

    Thread Starter Member

    Oct 4, 2012
    53
    1
    Hey Guys!

    I need some help locating a problem within a DJ mixer. I recently posted in this forum regarding a problem with the same type of DJ mixer and was actually able to resolve the problem completely. I'm hoping for good luck again! The problem is different than the last but hopefully you guys can lead me in the correct direction of solving it. Generally, the mixer itself will not power up and does not turn on (no lights). The individual PCB's inside the mixer seem to be receiving power as I tested some voltage points and I'm receiving positive readings. I have the full service manual which includes schematics and will post that below. I will also link to my old thread regarding the same mixer if that will be of any help (there are pictures and such of the boards there). I will also be testing the SMD fuses on the boards just to make sure none of them are open and to ensure there are no shorts. I'll post the readings here once I'm done. Thanks guys!


    Service Manual/Schematics: http://www44.zippyshare.com/v/50017572/file.html
    Old Thread: http://forum.allaboutcircuits.com/showthread.php?t=87064

    EDIT: Might have found a problem. Can someone clarify? There are 11 or so SMD fuses within the mixer that if blow may cause this problem. If you reference page 101 on the schematic, you can see IC43 which I believe is a blown fuse. Now when I measure it, I get one side of the fuse with a value of ~3.3V and the other side with a zero value. Is this normal for a fuse or does this mean it's blown? When measuring all other SMD fuses I get readings on both sides and never a zero. Also, right above this fuse there is a measuring point that should be 3.3V but I'm also getting a zero reading there as well as some more measuring points directly above this. Referencing the schematic again on page 101, the measuring points I discussed are specifically to the direct left of R367 (V3R3 where I get a 0.00V reading), to the left of R255 (V+33 where I get a 0.01V reading), above C114 (V2R5 where I get 0.0V) and to the right of this at V1R2 where I also get 0.0V. These are obviously not the correct readings. Anyone care to comment on this? Thanks again guys.
     
    Last edited: Dec 22, 2013
  2. trader007

    Active Member

    Feb 27, 2010
    222
    19
    to check fuses, all you have to do is run an ohm meter across the two leads. 0 ohms means good fuse. open/no reading means bad fuse.
     
  3. mynamesalex

    Thread Starter Member

    Oct 4, 2012
    53
    1
    I believe the IC43 fuse mentioned earlier is open. After testing with a meter, I'm getting a positive value across this fuse while all others have values of zero (closed fuses).
     
  4. sheldons

    Well-Known Member

    Oct 26, 2011
    616
    101
    replace with a 1 ohm fusible and see if your unit works or the fusible burns....check first the resistance after the fuse isnt a low s/c reading-if it is you need to play my favourite game-hunt the short
     
  5. mynamesalex

    Thread Starter Member

    Oct 4, 2012
    53
    1
    Thanks for the replies, guys. Couple questions. I'm still fairly new at this but I learn quickly. 1) What is a fusible and would I solder it over the fuse or in place of the fuse? 2) Is there anyway to bypass the fuse temporarily with a resistor and where on the board would I solder it if so? 3) What are the rules for your favorite game of find the short? It sounds like a pretty fun game. Haha thanks again.
     
  6. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    It is a reson why fuses are placed in the first hand. And second a reson why they blow up. So now you should not replace them with a short. In your case it may be some problems in the power supply unit(bad caps like dried out ones). Causing the fuse to blow. Sometimes power spikes will also blow a fuse, it could be that you are lucky.
     
  7. mynamesalex

    Thread Starter Member

    Oct 4, 2012
    53
    1
    The only reason I would short the fuse is to see if the unit would power up. Any way for me to test anything else currently?
     
  8. sheldons

    Well-Known Member

    Oct 26, 2011
    616
    101
    remove the fuse-check for a lo resistance reading on the power rail the fuse feeds-if you have a short you need to disconnect things on that rail untill you find the failed part -a fusible resistor is a safety component that is designed to go open circuit if a high fault current is passed through it-is also a quick way to remove the fuse,solder a 1 ohm fusible in its place and see what happens-if the resistor fails it will at least prove the fault is hopefully localised to a specific part of the circuit-in which case you will have to play hunt the short on that power rail until you find the failure
     
  9. mynamesalex

    Thread Starter Member

    Oct 4, 2012
    53
    1
    Thanks for the info. How do I check for low resistance and find the power rail that the fuse is feeding within the schematic?
     
  10. sheldons

    Well-Known Member

    Oct 26, 2011
    616
    101
    without the schematic its a lot of work but it can be done-what you need to do is set you meter to read resistance-when i do this i use my old avo 8 and you need to trace all connections on the pcb track directly after your fuse-if you find a short to ground after your failed fuse it helps to desolder one side of various components-wire links etc that are electrically connected to that pcb track-eventually you will find the short and simple component checks should reveal the cause-take your time as you do this.
    playing hunt the short seems to be my favourite pastime of late as ive had a couple of lcd power supply failures which when ive gone through checking point to point lifting one side of links and various other components the failures were not even on the power supply panels themselves,so a lot of patience is required when doing this.ive been in the trade for a good 25 years now and find faults i come across seem to follow a set pattern sometimes .
     
  11. mynamesalex

    Thread Starter Member

    Oct 4, 2012
    53
    1
    Hm awesome I'll try to look into this. Keep in mind I posted the schematic in the first post.
     
  12. sheldons

    Well-Known Member

    Oct 26, 2011
    616
    101
    yes iv just downloaded it......
     
  13. mynamesalex

    Thread Starter Member

    Oct 4, 2012
    53
    1
    If you want to take a look at the fuse/fuse feed in question take a look at page 101. You can see IC43 which I believe is the blown fuse. The measuring points which the fuse seems to feed are specifically on the schematic to the direct left of R367 (V3R3 where I get a 0.00V reading), to the left of R255 (V+33 where I get a 0.01V reading), above C114 (V2R5 where I get 0.0V) and to the right of this at V1R2 where I also get 0.0V.
     
  14. sheldons

    Well-Known Member

    Oct 26, 2011
    616
    101
    resistance is what you need-you need to see if you have a sc on that supply line......if you have you need to disconnect things to localize the fault
     
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