# My bass amp quit today - any ideas?



## james on bass (Feb 4, 2006)

I have a MarkBass Little Mark II which I've owned since 2008. It has done hundreds and hundreds of gigs without issue. 

Today I was setting up for a short gig. Set-up, tuned up and plugged in - everything working fine. Set everything aside while the rest of the band set-up. 

When we're asked to play a few songs, I go grab my bass and notice my amp is off. Weird, the power switch is on. Check the plugs, check the wall socket. Change power cords, change extension cord, plug into the power conditioner for PA which is on the same wall socket. Still nothing.

Quickly plug my Sansamp direct to the PA to do the gig. 

Afterwards, I pull the fuse and it is burnt black. I change the fuse, plug the amp in to the power conditioner and it doesn't even turn on. Pull that fuse and it is also fried. 









Do you think the amp's power unit is shot? Is this a major fix? I brought it home and took the outer cover off and there was a lot of built up dust in there, but no evidence of something burning or shorting out. I'm gonna blow/vacuum everything out even better tomorrow and hopefully find a couple replacement fuses. 

I really hope this thing ain't shot. It's been bullet proof for hundreds of gigs. 

I don't have a multi-meter, and wouldn't know how to use one anyway. 

Does anyone have any thoughts?


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## Church-Audio (Sep 27, 2014)

james on bass said:


> I have a MarkBass Little Mark II which I've owned since 2008. It has done hundreds and hundreds of gigs without issue.
> 
> Today I was setting up for a short gig. Set-up, tuned up and plugged in - everything working fine. Set everything aside while the rest of the band set-up.
> 
> ...


These are very well built amps. Can I say the repair will be cheap it all depends on what's wrong with it. One thing is for sure output transistors in this amp must be matched.... Or the repair will not last if that's what you need to get it back up and running. In other words don't take it to billy bobs amp repair to get it fixed. I would send this amp to the mark bass distributor if they do in house repairs. I have fixed more than a few they are great amps.


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## ampaholic (Sep 19, 2006)

It could be any number of things causing the fuse to blow so you'll want to take it t a qualified tech for sure but if it's any consolation I suspect most techs would say this is an easier problem to troubleshoot than an amp that occasionally blows fuses.
I'll defer to those more knowledgeable but if the fuse blows violently I'd be looking for a direct short and I assume that after checking the obvious stuff isolating stages is the best way to troubleshoot the problem.


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## dtsaudio (Apr 15, 2009)

These amps use a switchmode power supply. Chances are that's where the problem lies. You will need to contact the distributor (or your authorized dealer) for service.
The Canadian distributor is Erickson. They can tell you where to have it repaired.
http://www.eriksonmusic.com/


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## nonreverb (Sep 19, 2006)

For the fuse to blow instantly, it's usually one of two things. Output transistors, (FETs probably in this case) or a major power supply issue. Since it's a switching power supply, it would most likely be something on the primary side of the switching transformer such as one of the main filter caps or the chopper FET.
As stated, if this is a class D amp and it probably is, matching the FETs is critical.


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## dtsaudio (Apr 15, 2009)

> if this is a class D amp and it probably is, matching the FETs is critical.


It's not really a class D amp, just the power supply is switching. The power amp section is pretty textbook. It uses mosfets for the output and you are right they need to be matched.
I have to wonder what caused the failure. According to james, the amp was sitting there idling. Even with a clogged fan it wouldn't have been generating much heat. AC line spike maybe.
Power supply problem is just a guess based on another line of amps that used switching supplies. The predominate failure with them was power supply.


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## nonreverb (Sep 19, 2006)

You are correct although the MKIII is apparently class D now


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## dtsaudio (Apr 15, 2009)

That would suck. I have no use for class D amps. Too fragile, but a great way for Markbass to make more money.
They seem to be pretty closed mouth about how their amps operate.


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## james on bass (Feb 4, 2006)

Thanks for the help guys. Like I said, the amp has been great for 6 years and hundreds and hundreds of gigs. The fan was still spinning though it has always run warm. I'd been thinking the past year or so that the fan looked pretty dusty. When I took the lid off there was quite a bit of dust and dirt in there which I've blown out. I keep good care of the amp, but it has seen lots of outdoor, dusty shows over the years. I have the feeling that the power was rather sketchy where we were on Saturday which may have been what did it in. Now that it is nice and clean, I'm going to try a fresh fuse tonight and clean power at home. After that, it's gonna have to go in for service. Pretty sure I can get through the next two shows with my DI and the sound-guy giving me a mix in the monitors.


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## greco (Jul 15, 2007)

I'll be interested to know if a cleaning and fresh fuse bring about success. 

Good Luck (meant with sincerity , not being fecicious)

Please let us know.

Cheers

Dave


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## james on bass (Feb 4, 2006)

greco said:


> I'll be interested to know if a cleaning and fresh fuse bring about success.
> 
> Good Luck (meant with sincerity , not being fecicious)
> 
> ...


Nope, no change. Oh well, worth a shot. At least the tech this goes to will have a clean amp to deal with.


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## greco (Jul 15, 2007)

Thanks....Too bad there was no change.

Cheers

Dave


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## woodnoize (Jun 18, 2009)

our MarkBass Little Mark II head met a similar demise. & it worked sooooo well for sooooo long! then stopped completely. we cleaned it etc & it returned to form for a few more months but after that, it would only turn on for a few songs & crap out. as our tech said, "they don't make them to last any more". the good times with it were great thou.


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