RB-991 keeps blowing main fuse

[kingwilliam]

Hi all...

The problem: My RB-991 blew its main 12-amp fuse the other day (the fuse you can easily change from the back). I tried 10-amp fuses, but blew three in a row. No other components or speakers were hooked up to the amp. I unplugged the amp from the wall before swapping fuses.

There was no delay... put the fuse in, plug in the amp, turn on the power and "poof." The fuses were blackened on the inside.

History: Amp hasn't been used for a couple of years. It had an easy life before that. it worked fine for about half an hour, then the fuses started blowing.

Next step: Try a 12-amp fuse. (I could only easily find a 10-amp fuse... Trying a specialty store tomorrow). I didn't think the 10 vs. 12-amp difference would matter, but maybe it will. It'll be a slight inconvenience to drive across town to get a 12-amp fuse.

Help!... what could be going on? The store I bought it from isn't doing retail anymore, so can't help me.

thanks in advance.
b

[Glen B]

STOP !!! Do not try any more fuses. The fact that the main fuse is blackened means it is interrupting a substantial amount of current, such as you would get from a dead short. This suggests a possible major fault within the amp, maybe in the power supply.

The amp has internal fuses protecting the positive and negative output stage power supply rails which would have opened if there was problem such as one or more blown output transistors. Then you would not be getting repeated blown main fuses.

Repeatedly installing fresh fuses and applying power to the amp without first finding and fixing the problem, may result in further, more costly damage. Get the amp looked at by a reputable technician.

[kingwilliam]

Thanks, Glen.. Wish I had listened to your advice.

I found 12-amp fuses, and couldn't reist trying one.

I put in the fuse, plugged it in, hit the power button and "poof, poof", big sparks and smoke from both sides of the amp.

What's happened my amp?! Is it dead?

If I can get a free repair estimate, I guess it's worth checking into...
*sigh*
b

[Glen B]

Only a thorough evaluation will tell you how extensive the damage is. If the power transformer is still good and the damage is restricted to only the other power supply components, you may not do too badly. If you can pop the cover, take a picture of the insides and post it, I'm curious to see what kind of damage you have.