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Univox U150R Reverb Problem - Need Help and/or Correct Schematic

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  • #1

    Univox U150R Reverb Problem - Need Help and/or Correct Schematic

    Need the U-150R, I have the U-150RX schematic (close) but the reverb section is just different enough to make it a challenge.

    This will probably be clear as mud, but I'll give it a try.

    Return side of the reverb circuit seems to be working, but the send side driver and output transistors don't appear to be conducting. I have audio up to the base of the driver, the driver collector connects directly to the output base. No signal on the collector of the driver (or the output trans).

    I've ordered a replacement driver transistor 2N2219A (cross for 2SC876) and will try it when it comes in, but out of circuit it tests fine - beta and leakage tested with Sencore Trans tester.

    I've replaced the driver (2SC536F) which crosses to a 2N2222, no change.

    Any thoughts (or the correct schematic) would be greatly appreciated.
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  • #2
    Univox U150R Reverb Problem - Need Help and/or Correct Schematic

    Attached is the U-150RX (wrong) schematic.
    Attached Files

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    • #3
      Even though the transistors test fine, what is happening in the circuit voltage wise? Are the supply voltages getting to the 2 transistors? Are the transistors biased on?

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      • #4
        Could someone take a look at the attached schematic, per the OP the send side of the reverb circuit isn't working and appears to be a bias issue with the transistors.

        If I had to guess, the problem is with the 2N2222, and I suspect the circuit was changed and hasn't worked since.

        Since I couldn't find the schematic for a Unicord (Univox) U-150R, I drew one and have attached it. Hopefully I got close with it.

        The two 33K resistors off the base of the 2N2222 are suspect in that they are 1watt resistors and glued to back of the circuit board, either a mod or a poorly done repair.

        Appreciate the help.
        Attached Files

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        • #5
          Pretty sure the 2N2222 base needs a path to a positive voltage source somewhere. The base resistors are for sure going to ground?
          Originally posted by Enzo
          I have a sign in my shop that says, "Never think up reasons not to check something."


          ​

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          • #6
            Yes, going to ground. I suspect the two 33k resistors in series off the base should be going to a positive source as well, setting up a voltage divider bias but this is how it came in.

            I'm also wondering if they are the correct value. As mentioned above, it looks like a very bad rework or mod job.

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