No announcement yet.

Fender Rumble 150 no sound into power amp section

  • Filter
  • Time
  • Show
Clear All
new posts

  • Fender Rumble 150 no sound into power amp section

    I picked up a Rumble 150 Bass Amp for $20, guy said he got it for free and doesn't work.
    It was obvious that it had been dropped, the cabinet was cracked on the sides where the main speaker box transitions to the am chassis top area.
    After taking it apart I found that a mouse had been inside and chewed some wires all the way through pilot LED wires and through the insulation of the main 100 wires.
    After repairing the wires I fired it up and the power LED turned on, so did the fan, so did the overdrive LED when the button was pushed.
    But no sound through it to speaker.
    I suspected the main power amp section, but when plugging in the headphones it made some slight crackling.
    It did have a VERY small distorted signal through the headphone output.
    I hooked up a CD player t the Aux inputs and more detectable distorted signal through headphones.
    After looking at the schematic, I see that it has a dedicated (separately manufactured by Ice Power Denmark) power amp section that also delivers the DC power.
    It also has a disable function that is activated by the headphone jack.
    So the first attempt as diagnosing the issue was to disconnect the preamp section by clipping the W8 connection.
    After doing that the aux input to headphone portion was now very loud but also very distorted with line level.
    Plugging in a guitar into the aux was also loud and distorted but I could turn it down to non-distorted sound.
    But still no sound through the power amp after disconnecting headphones.
    I checked the Ice Power amp alone and it works fine as the power section (good thing since it is micro small circuit board components)
    So the issue is within the Fender boards somewhere.

    I figured this would be the best place to ask if for help.
    Solid state are not a big draw but you guys are way better than I at amp problem diagnoses.
    (Attached is a picture of the second half of the Fender section before it goes in the 50ASX2 power amp.)

  • #2
    There must've been some non-visible break in the trace on the board.
    This board has a dark shellac over the traces, very difficult to see the traces - just the thickness changes.
    It actually looks pristine. I reflowed some of those tiny solder joints without any changes.
    But after checking around, the +15.5 vdc wasn't getting past the first U7 transistor.
    I simply added a small jumper wire to supply the missing power and everything is working fine now.
    Not worth any further investigation - the trace/path was broken somehow.