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Schematic for Fender Sidekick Keyboard 60?

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  • #16
    Nice amp, well made for a reasonable cost by some Japanese OEM supplier.
    1) make a lamp bulb limiter and use it,.

    2) replace that bridge witrh a generic one.
    200VPI, probably 4 to 6A.
    Browse Mouser's catalog and pick one.

    Also replace the ceramic 0.5 ohms.

    Then to transistors:
    It will be easier for you to measure the power and driver transistors because they are outside the PCB with their own mini PCB to hold the wires, so unsolder (with a good pump) each one in turn from it and measure it with the diode test function out of circuit.
    Label each miniPCB so you don't confuse them when replacing.

    Post results.

    I suspect outputs and drivers a lot, maybe Q4 and Q5 are next in the line; also Q5, the bias transistor.

    Measure outputs and drivers first, post results.
    Juan Manuel Fahey

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    • #17
      Originally posted by J M Fahey View Post
      Nice amp, well made for a reasonable cost by some Japanese OEM supplier.
      1) make a lamp bulb limiter and use it,.

      2) replace that bridge witrh a generic one.
      200VPI, probably 4 to 6A.
      Browse Mouser's catalog and pick one.

      Also replace the ceramic 0.5 ohms.
      Have the lamp supply in progress.

      I've replaced the rectifier with a 200v 4A model.

      I ordered new resistors, might take a week.

      The old 0.5 ohm ones measured 0.9 and 1.1 (hottest one, with the crack) respectively.
      The old 750 ohm resistors had one at spec (747) , but the other was way out (for a 5 percent) at 827 (the hotter one)

      Will test the transistors soon, starting with the one (circled in pictures) that was connected to the hottest ceramic resistor.

      Is it necessary to replace with the same 2SD1046E model, or can one use the 2SD1046D model? NTE36 is indicated for the 2SD1046E model. I can get the D variant on ebay for a decent price if the HFE isn't that critical.

      1A HFE for E model is 100 and 200, HFE for D model is 60 and 120...NTE36 spec says 60 -?- 200 (not defined like the others)

      Thanks for the process guide.

      Robert

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      • #18
        You cannot go wrong with this seller.
        3pcs 2SD1046E Original Pulls Sanyo Transistor D1046E | eBay

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        • #19
          Is it necessary to replace with the same 2SD1046E model, or can one use the 2SD1046D model?
          Personally I'd avoid EBay or unknown "pulls" (unless I had pulled them myself and was 100% certain).
          Go for a reputable seller like Mouser/Digikey/Farnell/etc.
          The "gain" letter is not that important, all of them will work; Japanese just have this (good) custom of measuring each transistor and separating them in Hfe groups (sometimes they apply a dash of paint) but try to get the originals, not replacements.

          In fact you can replace both driver/power pairs with TIP142/147, and that's what *I* would do, if I had it in my bench, because I have over 100 each within arm's reach .

          But first check whether outputs are dead or not.
          Juan Manuel Fahey

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          • #20
            TIP142/147 are great parts, but they are darlingtons, and I believe the originals are not.
            Education is what you're left with after you have forgotten what you have learned.

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            • #21
              Correct, the original *outputs* are not, but I said "driver/power pairs" , meaning I intend to replace each driver+power pair with a proper polarity Darlington pair.
              The top pair *is* already a Darlington so it's a direct replacement, just juggling a little the wires.
              The bottom pair is a Quasi complementary pair, which could be called "a fake darlington" .... it can be replaced by a true one any day , also juggling the wires.

              In fact, I'll need 3 less wires for each pair, follow them to see which ones stay.

              This replacement has only one (easy to solve) "problem": it will require one more "diode drop" in bias voltage, which in this particular case is easy, just add an extra diode, in series with the two already there, and in contact with the heatsink.

              The original BE resistors, R42/R45 (150r each) must be pulled from the PCB, the Darlingtons already have their own ones inside.

              See the "OLD" original and the "NEW" easier/cheaper/stronger solution.

              Click image for larger version

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              Juan Manuel Fahey

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              • #22
                Thanks for the suggestion of the TIP series...I will consider that. Here is the update.

                I've changed out the rectifier for a 200v 4A one.
                I've swapped out the 2 x0.5ohm 5W power resistors (ceramic) with 2 spot-on replacements.
                Replaced the 2 750 ohm ones (the new read 739 each)

                Fired it up using a light bulb power supply (4W)...and it came on, stayed on...limiter lights dimly lit.
                No sounds from speakers at all... so decomposed the cabinet, and found that all disconnected...probably when I pulled the amp, but maybe from the original owner doing same, don't know.

                5 inch speaker had something inside it rolling around, surely would resonate once powered, so drilled a small hole in the metal casing, and extracted that (piece of solder from inside), taped back up, 4 layers electrical. It works fine.

                Connected speakers back up per schematic, and powered on, limiter lights off this time, very quiet 60 cycle hum from main speaker. But nothing amplified sounding (the hum didn't sound amplified as they tend to do, with that brighter aspect to the hum when an amp is working). No scratching or static when turning up volume, and nothing when I plugged in a guitar.

                That indicate the output transistors are bad, or should I check something else, first?

                Thanks for the guidance.

                (I don't trust that ebay parts puller really...their feedbacks are kind of spotty, and their prices are high to me).

                Only thing I am unclear on with the TIP replacement is your mention of the diode in combination with 'in contact with the heatsink'...?

                You mean Diodes D11 and D12, correct? If I can figure out the wiring, and they will sound the same or better, I'm fine with swapping out with the more plentiful TIP142/147 option. I can pick up 2 pair for $10 shipped (activeparts)

                One of those had an F and T option I think though (TIP142) at the NTE reference (NTE270 and NTE271 cross ref for these)

                Robert

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                • #23
                  Personally I would replace the 2SD1046 with the NJW0281G. The minimum Hfe is a little lower, but I bet it would work fine anyway.
                  "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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                  • #24
                    I see that I already botched the procedure (no speakers) , sorry...

                    For the suspect power trans 2SD1046E which had the hottest power resistor scorching, B-C and B-E diode test provides about 533mv, uni-directional (Fluke MM), pulling the rest now.
                    rc

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                    • #25
                      Originally posted by Artly There View Post
                      I see that I already botched the procedure (no speakers) , sorry...

                      For the suspect power trans 2SD1046E which had the hottest power resistor scorching, B-C and B-E diode test provides about 533mv, uni-directional (Fluke MM), pulling the rest now.
                      rc
                      Turns out upon getting ready to remove the wires, that one of the power transistors had a broken/weak solder joint...a loose wire...green one (the 313E for Q5)

                      Soldered that, it all worked again, amp-y sounding.

                      Turned off, tested them all anyway, they all checked out at about 590mv (diode test) each way, though the other 1046 checked as 550, but correctly.None seemed shorted.

                      So tested with guitar...

                      All 3 inputs work, though #2 has a bad volume pot which cuts the channel in and out, and the only thing that seems to heat up abnormally at all, are the pair of 750 ohm resistors. They get hot. (less then boiling though, per the saliva test No ssszzz.

                      Is it possible that a prior owner just cranked this up to the point where things pulled too much juice through the rectifier and it melted it and that was all that was really wrong with it? (plus the green wire connect?)

                      Or maybe the speaker connects came loose and shorted down below?

                      Seems to work. Left it on a few minutes, nothing smoking, boiling or otherwise suspect.

                      Robert

                      Comment


                      • #26
                        Originally posted by mitch66 View Post


                        Yes... I was thinking exactly the same thing... something else caused them to burn.
                        When the OP mentioned 2 burnt resistors... I was thinking it might be a known defect
                        with a known solution. In my case it was R85, R86. they are fried Black.

                        Has anybody else seen this before with R85 R86 ?
                        Had the same exact issues. Replaced both resistors with better 10k's is there something that caused them to burn out? My amp wasnt grounded by the previous owner, which I think might have caused a problem. I switched out all the pots and jacks, but need to go back and see where the circuit is breaking cause now there's no audio output.

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