Today, somebody donated an Akay AA-MBL radio/amplifier to me. Not operational, on investigation two blown 15 amp fuses, by the look of it, in the power amplifier. Fuses replaced by 2X 6 amp , and to my surprise, everything started working.
"Something" caused a momentary high current drain that popped the fuses, which sacrificed their existance to save the equipment. What this "something" was is not always obvious. It could have been due to cranking up the volume and clipping the amp for an extended period. It could have been due to brief high line voltage. It could have been due to kicking the power cord, causing an intermittent connection at the wall socket or cable socket on the amp. It could be due to thermal fatigue.
To answer the question you're /really/ asking, but didn't ask... It's quite possible for fuses to blow without there actually being anything permanently "wrong" with the amplifier. The probability that this amp is defective in a way that will cause it to explode or burst into flames is small.
Where in the circuit are the fuses? If they are line fuses, it is pretty hard to develop enough current through the power transformer [?] to blow 15A fuses. If there is an outlet for a phonograph after the fuses, it could have been a short plugged into that. I did have one set that the 'line' capacitor failed and it was blasted to oblivon so the set worked fine with a new fuse. The only clue that the cap had been there was a bit of blackening near the tie strip and two short leads with nice copper balls on the ends. Someone must have taken the bottom off and removed all the bits of plastic and paper since there were none present.
Driving a low-impedance speaker at high volumes can cause this. (I had it happen once.)
LET ME REPEAT, because no one seems to be paying attention. A fuse (or fuses) can pop for no /obvious/ reason. It doesn't mean the amplifier is defective, or that the fuses are likely to blow again. This sort of thing happens every day, and is nothing to worry about. *
If it /keeps/ happening, /then/ you have to find out why. Otherwise, don't worry about it.
The last time this happened to me was about nine months ago. I accidentally knocked the power cord out of an amplifier's AC socket. In putting it back, I didn't push the connector in quickly and firmly enough, and the amplifier "chattered" on and off. The inductive kickback generated enough current to blow the AC fuse. This was completely normal, one of the reasons electronic equipment is fused.
I once serviced a ReVox open-reel tape deck that kept blowing its fuse. The fuse popped every three or four times the unit was turned on. I watched the fuse during turn-on, and saw it flex as it heated up from the inrush current. After a few flexes, it broke.
Though it appeared to be the correct fuse for this deck, I decided to replace it with a slow-blow fuse of slightly higher capacity (about a half ampere, IIRC). The customer was happy, and as far as I know, the deck didn't explode and his house didn't burn down.
My brother-in-law had a problem with his stereo when he moved into a 'new' house. The place has 8 built-in speakers and he has a state of the art surround sound power amp. But when he cranks the volume up, the amp shuts down (solid state protection, no fuses were harmed).
So I did a bit of poking around. First thing, the speaker jack plate on the wall had only two pairs of terminals. Left and right, we assumed. Bad news, as it was probably wired with 4 speakers in parallel to each side. Then I popped the wall plate off. All 8 speakers were wired to one terminal pair. The right power amp was driving 8 paralleled speakers. The left power amp drove nothing.
Fortunately, all of the speaker wiring came down behind the terminal plate. And his amp has (more than) eight outputs. So now they all get their own speaker.
Paul Hovnanian mailto:Paul@Hovnanian.com