Home repair of power amp..............

EricH

I may have blown a cap in my Anthem MCA3. The wires on one channel were crossed for about 5 hrs. while I was at work and my speakers were breaking in. Hopefully it's just a fuse.I was wondering about fixing this thing myself instead of the $100/hr labor and cross/border shipping. If it is a cap or resistor, is this something that can be done at home with a call to Parts Express, a soldering iron, and a steady hand? I'm going to tear into it tonight.

bknauss

You probably blew something in the output stage, and that could mean either playing with big/easy parts to solder, or it could mean dealing with surface mount devices... surface mount devices can be a REAL pain, and can be impossible without a proper soldering iron and/or temp. removing other parts to gain access to the parts in question.

But hey, if it looks like an easy fix, you look set to go.

EricH

Thanks. Anything sounds better than shipping a 50 lb. amp to Canada.

bknauss

I definitely hear ya on that.
Was $100/hr the quote or an overstatement... I'm hoping it was an overstatement.

jarros

If you are going to try to fix it yourself, MAKE SURE you leave it unplugged for at least a day. The capacitors can stay charged for quite a long period of time. The last thing you want is a lethal shock while trying to fix your amp. Then the $100/hr labor charges won't look so bad...

It's good to have a anti-static wrist strap when working with open electronics like that. Attach it to the ground of your amp.

When you're looking for blown caps, they'll often be bulging at the top of the cap.

Other than that, good luck, and be careful!:D

DarqueKnight

Originally posted by jarros
If you are going to try to fix it yourself, MAKE SURE you leave it unplugged for at least a day.

Depending on the capacitor and the circuit design, capacitors can remain charged for far longer than one day.

The best practice is to drain off the charge through an appropriate resistor that is connected to ground. The amplifier's service manual should be obtained and consulted prior to doing any work.

jarros

Originally posted by DarqueKnight
Depending on the capacitor and the circuit design, capacitors can remain charged for far longer than one day.

Right. Most TV repair shops will leave the TV unplugged for a whole weekend (or more) because of this. I just wanted to make sure that EricH didn't go strait into trying to repair it without giving the caps some time to discharge a little.

nadams

A lot of TV places actually use capacitor dischargers to render the power circuits safe. Or just know where not to stick your screwdriver :P

EricH

Thanks for all the replies. I was away fron the computer this weekend, and had no idea that I was in danger while tearing that thing apart! That's definitley good advice that I won't forget.

It wound up being just a fuse. I was told by Anthem, and the circuit board said 15 amp FB, but it has 10 amp fuses in it. Also, 10 amp was all I could find in that size, and it says 125 volts on the side of the fuse, but the box states that it can be used in up to 250 volt applications. Is this just a matter of it being cheaper to manufacture one fuse and use it in two applications? This fuse and element looks identical to the one removed.

And yes, Anthem stated $100 US per hour labor rate. I think they didn't want me to fix it, so I'd just buy another amp.

danger boy

nice and i bet you're thrilled it was only a fuse. a couple bucks fix and you're ready to go again. congrats.

EricH

Yep, saved $400 on sending it in.