Need Ideas to Fix a Fender Rumble Amp

Discussion in 'Tech-Talk' started by Oldguitarguy, Sep 19, 2019.

  1. Oldguitarguy

    Oldguitarguy Squier-Meister

    308
    Mar 2, 2019
    Nj
    D1A92D7A-D3E9-4C04-BCFE-3CE736CBD1C7.jpeg I have this Fender Rumble 15 amp that now hisses louder and louder when I turn it on, even without any input plugged in. I tried Deoxing the pots with no improvement. Any ideas on the source of the problem and how to fix it?
     
    Kenneth Mountain likes this.
  2. drewcp

    drewcp Squier-holic

    Age:
    35
    Dec 14, 2018
    Saint Paul, MN
    If you plug an instrument into it, and set the instrument volume to zero, does it get better worse or stay the same?
     
  3. Oldguitarguy

    Oldguitarguy Squier-Meister

    308
    Mar 2, 2019
    Nj
    Stays the same.
     
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  4. mrriggs

    mrriggs Squier-Meister

    Age:
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    298
    Apr 27, 2018
    Vancouver, WA
    I'd start by checking the electrolytic capacitors. When electronics die, nine times out of ten its the electrolytic caps.

    Electrolytic capacitors look like tiny aluminum cans. As they age, their internal resistance goes up and they start running warmer. They can get hot enough to steam the electrolyte which will cause the can to swell or even burst open.

    The quickest check is to simply look at them. If the can is swelled, burst open, or leaking onto the circuit board then it needs to be replaced.

    An in-circuit ESR meter can measure the internal resistance and tell you which ones are bad, even if they don't show any external physical signs yet.

    Capacitors are super cheap and replacing them is not difficult. Get proficient at it and you'll be able to fix dang near anything.
     
  5. Oldguitarguy

    Oldguitarguy Squier-Meister

    308
    Mar 2, 2019
    Nj
    Thanks. Makes sense. Will check them. I also have a Fender FM212R that the seller told me will cut out after being played for a while and being pushed. I have not been able to replicate (good news). Do you think this issue could be caused by the same issue when it heats up?
     
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  6. Kenneth Mountain

    Kenneth Mountain Squier-Axpert

    the 212 sounds like a solder joint ?
     
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  7. kniah

    kniah Squier-Meister

    190
    Jan 30, 2019
    Waltham, MA
    I have a Rumble 25 of that same generation that would output distorted sound at any volume. Replacing all of the caps fixed the problem. Good place to start.

    Just be careful as the PCBs are fairly fragile. I had some traces pull off of the board when disconnecting some of the spade connectors (fixed with some structural epoxy but best to avoid in the first place).
     
  8. Oldguitarguy

    Oldguitarguy Squier-Meister

    308
    Mar 2, 2019
    Nj
    How do I identify the right caps to buy and do you have a suggested source?
     
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  9. Oldguitarguy

    Oldguitarguy Squier-Meister

    308
    Mar 2, 2019
    Nj
    Are they easy to find? Just look over the board and connectors and look for small cracks and then reheat with solder gun to re-fuse the solder?
     
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  10. Kenneth Mountain

    Kenneth Mountain Squier-Axpert

    Something near the source of the heat ? the schematics are available for all these amps - yes if you see something suspicious - carefully re-flow the solder
     
  11. kniah

    kniah Squier-Meister

    190
    Jan 30, 2019
    Waltham, MA
    I found a couple of threads on the Rumble 25 that mentioned a few likely suspects but I ended up replacing all of them. I pulled the PCB out and was able to see the cap values and voltage/temperature ratings and ordered equivalents from Digikey. I can post exactly what I ordered after I get home from work if that would be helpful. The Rumble 15 that you have probably uses similar components.
     
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  12. kniah

    kniah Squier-Meister

    190
    Jan 30, 2019
    Waltham, MA
    Here's a list of the replacement capacitors that I ordered for my Rumble 25. The only one I didn't replace was the 0.33uf. The caps highlighted in orange are the "usual suspects" that most commonly fail and cause issues. Total cost with shipping from Digikey was $14.41 for one amp's worth including a few spares. Hope this helps!

    [​IMG]

    [​IMG]

    [​IMG]
     
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  13. VMamp

    VMamp Squier-Meister

    Age:
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    112
    Jan 28, 2019
    United Kingdom
    I am retired now, though I still make Valve amps, and used to run a repair shop that did the repairs for the local music stores in my area. That type of fault really needs a a schematic diagram and an oscilloscope to verify which stage the noise is being generated in. You may well end up spending a lot of time replacing components only to find the fault remains. With a solid state amp it could equally be one of the Op-Amps, an experienced engineer with the equipment and experience in fault finding often works out to be a cheaper option.
     
  14. kniah

    kniah Squier-Meister

    190
    Jan 30, 2019
    Waltham, MA
    This is for sure the right approach. However, for these small practice amps I'm not sure it's economical to pay a tech to repair? I had enough confidence for my particular problem that it was a cap based on reading about other folks that had similar problems to give it a shot. I would have loved to do more diagnosis but had a hard time finding a schematic for these first generation Rumbles (did find one for a 3rd gen amp). I'm not sure if a cap issue is affecting this amp but if you find other people with similar symptoms who post remedies you can make a somewhat informed decision. Good luck!
     
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  15. Oldguitarguy

    Oldguitarguy Squier-Meister

    308
    Mar 2, 2019
    Nj
    761C313D-2203-4558-BF6B-095428005AF4.jpeg 97AD3E82-8FE5-473E-9769-368DDAC754EC.jpeg So I took out the board and could not find any bulging capacitors or problem solder joints by eye, so I deoxed all the pots and connections and it didn’t help. Here are pics of the board. Any further thoughts?
     
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  16. SubSailer671

    SubSailer671 Squier-Meister

    260
    Jul 4, 2019
    Ohio, United States
    It's hard to tell from a photo, but I don't see any cold, disturbed, or broken solder joints on the back side of the board. The front side photo doesn't indicate any capacitors swelling either. If it were on my bench, the next step would be to break out the oscilloscope and trace the signal path.
     
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  17. kniah

    kniah Squier-Meister

    190
    Jan 30, 2019
    Waltham, MA
    It looks like there are some scorch marks on the solder joints for what I think is the power amp (hopefully someone with more electrical knowledge than me can chime in here):

    [​IMG]

    I'm assuming there was a heatsink of some kind attached to this chip (judging by the orphan screw through it)? If you can read the P/N on that chip you can look up the datasheet for it and do some diagnosis with a simple multimeter (just have a steady hand and be careful not to short any of the leads with your meter).

    For what it's worth, none of the caps in my Rumble 25 showed any signs of bulging or leaking but replacing them did fix my problem (lots of distortion at any volume).
     
  18. SubSailer671

    SubSailer671 Squier-Meister

    260
    Jul 4, 2019
    Ohio, United States
    Those marks are normal for a heat generating device. It would take a close inspection (and maybe a multimeter) to determine if the solder joints are damaged or the pads lifted due to heat. From this photo it doesn't look like it to me.
     
  19. SubSailer671

    SubSailer671 Squier-Meister

    260
    Jul 4, 2019
    Ohio, United States
    Just for giggles have you tried plugging it in somewhere else? Maybe take it to a neighbor's house and try it there?
     
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  20. Oldguitarguy

    Oldguitarguy Squier-Meister

    308
    Mar 2, 2019
    Nj
    Yes. Different spots Around the house. Same Noise. Thanks.
     
    Kenneth Mountain likes this.
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