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replacement Boss DB-90 jack

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  • replacement Boss DB-90 jack

    I have been doing some volunteer repair work for my local high school's music department. The music director is great but finances are always tight for school music departments. The latest is a Boss DB-90 Dr. Beat met. The symptom is that the internal speaker seems to not work but the root cause is the 1/4" line out jack has been torqued and the switch which normally enables the speaker when a cable is not plugged in is damaged. I've been totally striking out finding a source for a replacement. The jack appears to be from the Kunming HTJ-064-04A line. Here is a link to the mechanical drawing from Kunming:

    The particular version on the DB-90 is one where terminals 1-5 are present (ground, tip, ring, and two for a switch and the switch is normally closed and in both states is isolated from the other 3 terminals) and terminals 7-8 are not. The jack does say Kunming on it and my calipers seem to say that the part in hand matches the drawing. The Kunming web site does not list a North American distributor (I'm in the Southeastern US).

    Anyone have any ideas on where to get a replacement? I tried the Boss web site but it wants me to register the DB-90 and I have none of the required info (not even the serial number, I'm assuming that fell off in the rain or heat at one point as this unit gets used both in the classroom and outside in the summer in the heat for marching band).

    In case anyone else runs across this the audio amp output goes onto the jack board and through a series combination of 2 normally closed switches. One is for the 1/4" line out and the other for the 1/8" headphone out. Then the signal comes back and heads towards the speaker (maybe through the other half of the audio amp, I quit tracing when I found the bad jack). So the idea is plugging into either of those two connectors will mute the internal speaker.

    Rant: What is with these !@#$ plastic connectors!!! I also just repaired a rather expensive Yamaha synth with damaged plastic connectors. Ebay yielded parts for that.

    Thanks so much in advance for any help.

  • #2
    Plastic connectors are insulated from the chassis. Even ones with metal mounting bushings still have plastic bodies.

    You could call Roland in California and ask if they can supply the part. Tell them Boss DB-90, not the Kunming stuff. Call them on the phone, don't rely on web sites.

    Looking at the board, are all those contacts in use? Sometimes they use the same jack for all functions even though not all need all the contacts. For example, the phones jack probably wants most of them, but the start stop jack might only need tip and sleeve. If the start/stop jack has all the contacts, you might be able to steal it for the phones. and use a simple Jalco jack in place of it for the start.

    Hard to see in this picture, but I suspect this jack works:
    Yamaha Parts ΒΌ inch RDJ 06 MC02 Series Phone Jack LX801220 | eBay

    I have a couple of those new in stock, I also have a few used pulls that ought to work. If we can see a photo of the circuit board solder side, or better photos of your jack...
    Education is what you're left with after you have forgotten what you have learned.


    • #3
      Yes, all the contacts are in use. The signal is mono but then connects to each of tip and ring via a series resistor. The two switch terminals are isolated from the rest and are used for enabling the internal speaker.

      Unfortunately the other jacks on the board are different and don't have the switch portion but that is a good thought.

      Here is the top of the board. I'm pointing at the jack which is bad.
      Click image for larger version

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      And here is the bottom of the board. The jack has been removed and is sitting just to the left of where it was. The terminal at the north is ground, the two at the south are tip and ring and the two in the middle offset to the right are the two switch terminals (closed when nothing is plugged in)
      Click image for larger version

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      And finally this is the bottom of the jack itself.
      Click image for larger version

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      The PDF I linked to in my original post has the exact dimensions. I verified with calipers that the part in hand has the same dimensions as the part in that Kunming drawing.

      I'll give Roland a call and see if I can get anywhere.

      On that Yamaha jack, is there a mechanical drawing somewhere so I could compare it?



      • #4
        I didn't doubt your drawing, but I wanted to see the jack, I find it more informative than the drawing. I am sure there exists drawings of the part Yamaha uses, but have no idea where they would be. Yamaha wouldn;t publish them, no need. Your jack is a common enough type, and appears to be a standard 7- or 9-pin with a couple snipped off.

        There are a number of jacks with same shape and footprint that do not look identical, but are the same electrically.
        Education is what you're left with after you have forgotten what you have learned.


        • #5
          I think that the jack is YKB21-5005 sold by Jalco but still it is very difficult to be purchased. See the catalogue. I've seen YKB21-5006 but I'm afraid it's different.



          EDIT: that's funny. I just found it in a shop in Poland:

          But it looks like there are several versions of the jack. You can check it here:

          It seems that you need version 3C, or 3E with removed two pins.

          E-mail to Jalco:
          Last edited by MarkusBass; 07-04-2016, 12:15 PM.