Announcement

Collapse
No announcement yet.

Seismic Audio Plate Amp no drive

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

  • Seismic Audio Plate Amp no drive

    Subwoofer section had blown outputs and drivers plus burned traces on the power supply board. I replaced and repaired everything, but subbed mje15032/33's for the driver/predrivers. The signal looks good until a load is hooked up and then it collapses and never attempts to draw any current. I've checked all my emmiter and base resistors, I have no DC offset, the opamp has been replaced, bias transistor replaced. I'm starting to think these mje's are just different enough to keep the amp from working. What am I missing?

    With scope attached at the amp output,
    No speaker load:
    Click image for larger version  Name:	20230425_112323.jpg Views:	4 Size:	4.96 MB ID:	981358
    With Speaker load:
    Click image for larger version  Name:	20230425_112352.jpg Views:	0 Size:	5.05 MB ID:	981360
    Attached Files
    Last edited by tdlunsfo; 04-25-2023, 04:35 PM.

  • #2
    Are the current limiters OK?
    Click image for larger version

Name:	Screenshot 2023-04-25 at 19.20.51.png
Views:	128
Size:	39.0 KB
ID:	981366 If they are short ciruit, quite likely from the described carnage, you will have no current to drive the output transistors.
    Support for Fender, Laney, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk
    If you can't fix it, I probably can.

    Comment


    • #3
      MJE15032/33 for 2SA940 and 2SC2073 ? They look close enough to me.
      Does the bias adjust pot change the voltage across emitter resistors of output devices?
      Originally posted by Enzo
      I have a sign in my shop that says, "Never think up reasons not to check something."


      Comment


      • #4
        Originally posted by Jon Snell View Post
        Are the current limiters OK?
        Click image for larger version

Name:	Screenshot 2023-04-25 at 19.20.51.png
Views:	128
Size:	39.0 KB
ID:	981366 If they are short ciruit, quite likely from the described carnage, you will have no current to drive the output transistors.
        Welp... this was it. Sure enough, they show shorted. I was positive I checked these and at one point I even desoldered the emitters just to rule them out. I removed them from circuit and voila... wattage.

        Comment


        • #5
          Don't forget to replace them ... or ... didn't they work?
          Whoops!
          Another not so good design that failed in a spectacular way

          Joking asside, pleased to help.
          Last edited by Jon Snell; 04-25-2023, 08:45 PM. Reason: Additional text.
          Support for Fender, Laney, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk
          If you can't fix it, I probably can.

          Comment


          • #6
            I replaced them and amp is back together. Sometimes a man just need another set of eyes to get his mind back in line. Much appreciated.

            Comment

            Working...
            X