Announcement

Collapse
No announcement yet.

Soundcraft Spirit Power Station -- dead Right channel power output

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Soundcraft Spirit Power Station -- dead Right channel power output

    Everything works except the Right output. All fuses OK. +/-60v rails OK on both channels. All voltages at connector CN5 are OK (see schematic snip, pasted below). Thanks to my new thermal camera, I spotted resistor R110 (highlighted in red) is cooking at over 400F. This appears to be part of the 5v regulator.

    So, considering the solder side of the PCB is not accessible without further disassembly, what's my logical next step? Thanks!

    Click image for larger version

Name:	snip.jpg
Views:	93
Size:	307.4 KB
ID:	982823
    Attached Files
    --
    I build and repair guitar amps
    http://amps.monkeymatic.com

  • #2
    I mean, can a LM317 still output 5v while drawing way too much current? Or maybe that C23 cap is shorted? DC resistance across C23 shows ~7K.
    --
    I build and repair guitar amps
    http://amps.monkeymatic.com

    Comment


    • #3
      What is the resistance across C40? now measure the same C40 res with con5 unplugged. Does the highlighted res still get hot with con 5 unplugged?

      The input current on LM317T is determined by the load current and the current flowing from the adjustment pin (Iadj). The input current is equal to the sum of these two currents1. The load current depends on the output voltage and the resistance of the load. The adjustment pin current is typically 50A and can be neglected in most cases​. (BingChat)

      Im thinking since the 317 puts out the 5V its possible the load is drawing too much current.
      Last edited by clintronics; 05-23-2023, 03:54 AM.

      Comment


      • #4
        That is a 2W resistor, it's supposed to get hot. Are you getting 5V out of that regulator? What is the voltage across the 33R resistor in question? 7V across it would still only be 1.5Watts.
        Any power supply fault should cause an issue for both sides.

        Comment


        • #5
          Originally posted by g1 View Post
          ......Any power supply fault should cause an issue for both sides.
          ^^^^^^ That.
          If you insert signal directly into the power amp inputs, do you get anything? It could just be a bad switching jack.

          "Yeah, well, you know, that's just, like, your opinion, man."

          Comment


          • #6
            Originally posted by clintronics View Post
            What is the resistance across C40? now measure the same C40 res with con5 unplugged.
            760R with con5 plugged in, 894R with con5 unplugged.


            Originally posted by clintronics View Post
            Does the highlighted res still get hot with con 5 unplugged?
            No!

            Originally posted by g1 View Post
            That is a 2W resistor, it's supposed to get hot. Are you getting 5V out of that regulator?
            Yes, +5v supply is OK.


            Originally posted by g1 View Post
            What is the voltage across the 33R resistor in question? 7V across it would still only be 1.5Watts.
            With con5 unplugged, voltage drop across R110 is only 0.2v. But with con5 plugged in, voltage drop is 7.6v. So, no worries here?


            If no worries here, I'm back to my original issue, which is that the Right channel output is dead. As I mentioned at top, I measured the 60v rails, which look good. Where do I go from here?
            --
            I build and repair guitar amps
            http://amps.monkeymatic.com

            Comment


            • #7
              You must have 0volts DC on L201 to work.
              Have you got 0volts? If you have does relay 2 pull in?
              Support for Fender, Laney, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk
              If you can't fix it, I probably can.

              Comment


              • #8
                I have very near 0v (4mv, 8mv) on L201 and L1 (the big inductors just prior to relays and speaker outputs). On working Left channel, relay works correctly and makes good connection to speaker output when energized, but Right channel does not. Here is a snip of the relay turn-on circuit:

                Click image for larger version  Name:	Screenshot 2023-05-24 at 9.20.47 AM.png Views:	0 Size:	52.3 KB ID:	982888

                Both D23 and D19 measure as diodes with 0.17v drop when tested in diode mode with my DMM. Measuring voltage drop across D23 when circuit is energized shows 24vDC, and across D19 shows 25vDC.

                So, does this data eliminate everything but a faulty relay for Right channel? And if yes, how do I spec the relay? It's marked "Potter & Brumfield T90 series". 24v, I think, based on schematic and voltage across diodes. What amperage?

                Maybe this one? https://www.amazon.com/TE-CONNECTIVI...dp/B0195UZNEI/
                --
                I build and repair guitar amps
                http://amps.monkeymatic.com

                Comment


                • #9
                  Originally posted by xtian View Post
                  Both D23 and D19 measure as diodes with 0.17v drop when tested in diode mode with my DMM.
                  Measured out of circuit?

                  - Own Opinions Only -

                  Comment


                  • #10
                    Originally posted by Helmholtz View Post
                    Measured out of circuit?
                    No, in circuit and unpowered.
                    --
                    I build and repair guitar amps
                    http://amps.monkeymatic.com

                    Comment


                    • #11
                      Originally posted by xtian View Post

                      No, in circuit and unpowered.
                      In circuit you're essentially measuring the voltage drop across the DCR of the coils.
                      Forward voltage of a 1N4001 should be around 0.6V.
                      - Own Opinions Only -

                      Comment


                      • #12
                        What do you recommend?
                        --
                        I build and repair guitar amps
                        http://amps.monkeymatic.com

                        Comment


                        • #13
                          Oops--owner just pulled the plug on this repair.
                          --
                          I build and repair guitar amps
                          http://amps.monkeymatic.com

                          Comment


                          • #14
                            Originally posted by xtian View Post
                            What do you recommend?
                            Of course measuring the diodes out of circuit.
                            In circuit diode measurement only makes sense if the surrounding circuit resistance is larger than maybe 10k.
                            - Own Opinions Only -

                            Comment


                            • #15
                              Originally posted by xtian View Post
                              What do you recommend?
                              Using a scope, if you got one.

                              Comment

                              Working...
                              X