Announcement

Collapse
No announcement yet.

Marshall JVM fuse

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

  • Marshall JVM fuse

    My friends JVM head is acting up. Its blowing the 10 amp fuse inside , FS4 . It is in the heater circuit . Im seeing 75vdc at fs4 and fs3 with no tubes in the amp. but then with my my current limiter hooked up to the power , its still showing a short somewhere.

    Looks like theres a bunch of stuff connected to the CT of this winding so im going to start looking there , Maybe one of those resistors or caps is shorting to ground? R81.82,82 ....C42 , 46, 47 , 49, 53

    I will try to attach the scem...
    Attached Files

  • #2
    I believe there is a mod to jump the 10amp filament fuses thereby eliminating them...glen

    Comment


    • #3
      are you serious ?

      Comment


      • #4
        I pulled the board today and tested everything i could see in that circuit. I had to re-flow A TON of joints in there....wow.

        other than that im not finding the cause ....

        i havent powered it back up yet though..

        Comment


        • #5
          did you ever find a cure valvehead?

          I also have a blow F4, and was wondering if you ever found the problem.?

          Comment


          • #6
            never did. The fuse never blew again .

            Comment


            • #7
              Yes,
              The mod is to jump the heater supply fuses FS3 & 4. They just blow inadvertantly.

              My take is they are slo blow variety around 10A fuses (as I recall) that just get too hot anyway (being coils as SB fuses are) & then the fuse clips are too whimpy & end up with low resistance connections with the fuses which further creates heat. They really should be of the pigtail variety.

              On top of that it seems in my experience filament just draw too much current at start up & tend to blow the fuses eventhough they're slo blow.

              They want you to remove the clips & hard wire them. I just wrap the jumpers around the clips & solder them as they are no longer going to get hot with an adequate guage wire.

              the bulletin came out 8-8-2007. I'm sure it's on the schemo page on the korg site...only accessible if you're authorized.

              Just found it...Find attached. glen
              Attached Files

              Comment

              Working...
              X