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Possible blown fuse in Rumble 40

Kenny056

Kenny056

Dec 1, 2023
408
1,825
#1
I let a friend borrow my Rumble 40 for use with his keyboard. I've played keyboards through all sorts of bass amps without issue, so i wasnt at all concerned. Well in this case he played for about 10 seconds and then it went pop. Now when I try to power it on, the power light briefly comes on and then fades out.

Any ideas how to remedy this? Thanks!
 
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#4
Superficially, without knowing much about the amp, it sounds more serious than a fuse. Plumbing in a keyboard doesn't sound like a likely cause unless the keyboard has some kind of mega serious electrical fault. I think you need someone with significant experience and test equipment.
 
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#5
It's not an amp I used often. I upgraded to the 100 fairly quickly after purchasing it. That's why I let the keyboard player use it. I use my Rumble 100 for my church gig. I just wanted to have it available for my children, as they're getting to the age where they starting their own band.

I'll see if I can find a local repair shop that won't charge an arm and a leg for such an inexpensive amp.
 
#6
Kenny056 said:
It's not an amp I used often. I upgraded to the 100 fairly quickly after purchasing it. That's why I let the keyboard player use it. I use my Rumble 100 for my church gig. I just wanted to have it available for my children, as they're getting to the age where they starting their own band.

I'll see if I can find a local repair shop that won't charge an arm and a leg for such an inexpensive amp.
Click to expand...
Was there anything about the cable used that was suspect?
 
#9
Well this is disappointing

My oldest child is 6 and he has an engineering mind. He and I might just make this a project, since it's probably not worth the money to have someone service it. I just checked it out again and when you power it on the power light flashes on for a split second and it lets out that little pop that it did when it was working. It then goes dead.

I should add that this amp is very nearly new. I played it once at church and that's it. Between rehearsal and service, it probably has less than 90 minutes playing time on it.

It worked perfectly when the keyboard got plugged into it. That's why I assumed it was keyboard related. You all certainly no much more than I do about this sort of stuff.

Any suggestions for where to start as far as diagnosing the issue?
 
#13
The keyboard being plugged into it just happens to be a coincidence.
Kenny056 said:
Any suggestions for where to start as far as diagnosing the issue?
Click to expand...

How experienced are you with repairing electronics?

As much as I like the idea of a project with your kiddo, something with less lethal parts (like a fuzz pedal) might be better project.
 
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#14
Relsom said:
I don't know anything about the Rumble 40, but is there a chance the guy was distracted and accidentally plugged his keyboard into an ext. cab output on the amp?
Click to expand...

My LD150 bass combo was left at church one time and when I came to use it next time it wouldn’t work. When I took it in for repair the technician said the preamp had been burnt out possibly by someone inserting a powered signal through the input socket such as a lead from a speaker out socket from another amp.

I don’t think anything from the keyboard would cause anything like this though. I assume he used the headphone socket on the keyboard? I’m no expert but what if the headphone out volume control on the keyboard was set at max volume, could this have damaged the preamp?
 
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#16
Kenny056 said:
Any suggestions for where to start as far as diagnosing the issue?
Click to expand...

Not really.

Diagnosing an amp with the symptoms you describe will take electronic equipment that a good electronic tech will have and know how to use.

That’s really the bottom line. It’s a given that the keyboard you plugged in didn’t cause that kind of problem. From what you describe, it’s gonna be an internal component problem.
 
#18
It’s not impossible the keyboard caused the problem, especially if the keyboard
involved has its own preamp for plugging direct into a power amp. That could have been a signal too hot for the preamp in the Rumble. It will still need diagnosed by a tech with the test gear required and knowledge of how to use it.
 
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#20
Ken R said:
I would call their customer service line and give them the serial number.
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This.
I don't know about your skills, but modern electronics isn't really serviceable by amateurs like me. I can wire guitars, make cables, that sort of thing, and even make up circuits on veroboard or the like, but modern circuit boards are a different game entirely. I was given an amp with a not too dissimilar fault a few years ago, and although I made some progress in finding out roughly where the fault was it was evident to me that I didn't even have the skills to replace components on a modern circuit board. They are not like they were in the 70s!

Even if you open it up and find a black and smoking component you still have to find out whether that was the cause or just a symptom. Some will argue that you can replace whole boards, not components, and that's true if you can get the parts, but unless you've managed to test everything how do you know which board it is? Or even more than one - if its a PSU problem it could conceivably have fried components on several boards.

Assuming its not repairable a better project with your lad might be to turn it into an extension cabinet or a wedge monitor, something of the kind.
 
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