Bass amplifier very loud hum....nothing plugged in, volume zero....

[CoolCat]

Just posting a DIY so maybe someone else will stumble across it and save a few bucks on a possible repair.

Bought a nice used solid state bass amp on craigslist lasted a month or so, went through practices and gigs., and then this week, an extreme loud buzz/hum. BUZZ/HUM Sound was very loud nothing plugged in and no volume.

Some articles mentioned swapping ac outlets, ac cords, then tapping on the head (which can be a caveman check for bad solder connections). When I gave the amphead a good punch the Hum disappeared.

Next was removing the amp from the combo/cab. plugging it in and as one poster mentioned, with a wood poker tap around and see if the loose component could be found. Other posters mentioned the Large Filter Caps next to the transformer are known for coming loose/cold solder joint/bad solder joint.
Poking with the wooden poker on the filter cap re-created the HUM/BUZZ.

Next was unplugging, disassembling and touching up the large filter cap solder joints locations. Problem fixed...

Time it took was about 45 minutes to 1hr.

Just thought I'd post to pass along the DIY repair notes for someone else.

Amp= Fender Bassman 400

 

[ranjam]

Normally, that happens to the cheap amplifiers that the board gets 'wave soldered' quickly at the factory. But I guess it can happen to the big names as well. Unless the Bassman 400 is made in China.

 

[CoolCat]

This is a Mexico built amp...and its wave soldered, I believe.

The root cause?
(the Bass player was jumping on & off the amp= broken solder joint? or/.. loading and vibration? )
It worked fine when I bought it for several weeks and one gig. IDK?
this one is 10yrs old -ish and came back to life.....

Anyway I was so glad others had posted the fix! the info got it repaired for free!!!

DIY .... rules....

 

[Beatrice three]

Ahoy,


I had this exact problem with my amp. Fender bass man 100 solid state. I took a look inside and sure enough the filter cap solder joints were messed up. So I soldered them back together, this was my first time soldering anything. I put it mostly back together and tested it now it just makes a low buzz and when I plug the bass in nothing happens.

I don't have much experience working in amps so any advice or help would be excellent.

 

[ecc83]

This is a common problem with any electronic equipment that uses heavy components just secured by solder.
In addition to just touching up the joints it is best to beef up the print with some 20guge solid wire (strip some coax telly downlead and tin it!) Then a blob of glue from a gun is a good move but not so much as to make further servicing a pain!

Some valve amps run heaters thru print tracks and these can get hot and "dry" at the holders and connectors. Run solid wire all the way along the track, scraping off the resist at intervals to tack it down. Some amps put fuses in the heater circuits. IMO this is daft and unnecessary and I would just short the fuse carrier but beware of local electrical legalities!

Beatrice three: Has a fuse blown? We will need photos.

Dave.

 

[Beatrice three]

Ecc83

Thanks for the reply!

The fuse looked fine, I can post some pics.

Another bit of info about my amp, I don't know what it means. But when I plugged it back in right after I resoldered the filter caps, it wasn't making sound so I tapped around the board a bit more and a spark happened which tripped the breaker in my room. I don't know if that means anything, the board didn't looked burnt up anywhere.

 

[ecc83]

Ecc83

Thanks for the reply!

The fuse looked fine, I can post some pics.

Another bit of info about my amp, I don't know what it means. But when I plugged it back in right after I resoldered the filter caps, it wasn't making sound so I tapped around the board a bit more and a spark happened which tripped the breaker in my room. I don't know if that means anything, the board didn't looked burnt up anywhere.

Get that amp to tech' PDQ! I don't kow where you are but people do not have circuit breakers in their rooms in the UK! (Well, ok, the bedroom/"studio" I am in is where the electrical service comes into the house but I would never expect the 40A breaker to trip nor the RCD)

To trip your circuit you must have a mains side fault in the amp and that is where the total noob stops and seeks professional help.

Dave.