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SVT4 PRO Reassembly Issue

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  • #1

    SVT4 PRO Reassembly Issue

    Hey guys-

    I had a problem with my 4 PRO- no A channel, B channel cutting in and out. It's a problem I've had before (broken pcb pad at a diode) and successfully repaired with a jumper. I went in to it again and saw that the jumper/diode were moving a little, so maybe a possible intermittent short. I glued it down tight.

    I was putting it back together, and when I got to reconnecting the xformer, I realized I had written down some of the connection points incorrectly. I guess my eyes aren't what they used to be. Looking at the schematics, I don't see specific "J" terminals for the twisted pair of orange wires coming from the xformer to the power board. IIRC, they go to J26 and J24. Can anyone confirm this for me? I can furnish pics if necessary. Thanks.
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  • #2
    Look at this thread and post #3 - Ampeg SVT 4 Pro schematic needed

    Enzo posted the schematic in multiple parts. See if this matches your amp.
    It's not just an amp, it's an adventure!

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    • #3
      Orange wires?
      Education is what you're left with after you have forgotten what you have learned.

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      • #4
        TomCarlos- Yes, I have those schematics, but (unless I missed something) they show that the xformer connects to a header with terminals 1-7. My board has a power board with a number of numbered J terminals. This arrangement does not match the schematic layout.

        Enzo- The wires on my particular unit are orange. I realize that other amps may use different colors. In my amp, there is only 1 set of 2 twisted wires that connect to the power board.

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        • #5
          I think we are missing something between us. The 7-pin header upper right on the page does not connect to the transformer, that is the cable to the preamp. Look on same page upper left, the transformer and all the J connectors are there. Also, look at the layout drawing, the 7-pin (J33) is on the small power supply board lower right. The J posts are on the main board. A pair of wires going to J24/J26 makes no sense.

          My problem is not so much the orange as it is the two twisted. There is no two-wire secondary. However the AC for the main rails might be twisted without the center tap wire. That would be two wires, the center tap run separately. But that goes to J27 and J29 right near the rectifier bridge DB1. The center tap goes on J28 which is nestled in between the four main filter caps.

          There are only two secondaries. One I just described, the other is not free wires, but has a three pin molex and plugs onto the little power supply board.
          Education is what you're left with after you have forgotten what you have learned.

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          • #6
            Watch this video - AMPEG SVT4PRO REPAIR

            Does this look like your unit? There are spots where you can get an idea of where the orange wires go, especially around the 18:20 minute mark.
            It's not just an amp, it's an adventure!
            • Likes 2

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            • #7
              Enzo- Perfect! That's exactly what I was looking for. In my notes, I wrote them down as J26 and J27. I'll try it out in the morning.

              TomCarlos- Yes, that twisted orange pair is exactly what I was referring to.

              Thanks to both of you for the help.

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