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-   -   Is this burned board repairable (http://www.diyaudio.com/forums/solid-state/4693-burned-board-repairable.html)

phishead8 21st July 2002 02:36 AM

Is this burned board repairable
 
2 Attachment(s)
A buddy of mine handed me his broken BGW 750C and asked if I could take a look at it. Always curious, but with little experience, I lugged it home and opened it up. Below is a picture of what I found. The right channel is intact and I can figure out most of the pieces using symmetry. Nothing looks more complicated than resistors and transistors and diodes. My question, however, is whether or not the traces of the PCB will hold up under such heat. Any suggestions? I suppose that I could P2P over the broken traces.
I guess another question is if I should suspect another part of the amplifier as the cause.
The transformer is extremely large and the whole unit weighs no less than 60 lbs. I'd gut it and build him another, but an approaching move prevents it.
Thanks for any help.
-Dan

JoeBob 21st July 2002 02:45 AM

It looks pretty fried. I've had traces die from less. I'd go p2p if it's simple enough. As for other problems, probe and check. A multimeter and a scope should be all you need.

jleaman 21st July 2002 06:18 AM

OUCH that looks bad .. if you can get a copy of the pcb ooff the othere channel if there is one then id strip it ( but draw out all the component places and posisions) and make a fresh new copy

Apogee 21st July 2002 05:23 PM

I'd make sure to check the outputs and the load resistors (the white square ones). Most likely, on the outputs that cooked, the load resistors might have also changed value due to the heat... You might consider replacing each when replacing its corresponding blown output transistor... Make sure you check EVERYTHING or you will just end up with another catastrophic failure... The amp is old enough at this point that even the caps are suspect...

That board didn't fry like this for the fun of it... What happened to it to make it die like this?

Before you return it to your friend you might ask if he's tested each of his speaker drivers with an ohm meter... My guess is he blew a driver and the amp was then driving a direct short. This caused it to blow one or more outputs which took out part of the driver stage with it...

It actually doesn't look that bad to me. The black is just smoke... Clean everything up and then see what you've got... If traces are actually gone then point to point what's missing.... I have a hunch that it's actually not that bad and is very salvageable...

You might also contact BGW and simply inquire about buying a new board... They are still in business... Go here:

http://www.bgw.com/

That amp was actually pretty good. Keep in mind it was designed for pro audio applications and therefore is not an audiophile amp... That having been said, they were very reliable and would be worth fixing for either PA use or a good bass amp with lots of zots...

Good luck,

Apogee 21st July 2002 06:00 PM

I was just exploring the BGW site a bit further... If you go to the tech support page, they list the modules and prices on the page...

http://www.bgw.com/tech/

Would be a quick way to bring the amp back depending on your budget...

I would still call and see if you could just buy a new board from them if you feel it's really necessary... I still think that I'd just repair the existing board though - I don't think it will take long...

phishead8 21st July 2002 07:15 PM

Thanks to everyone for your help. Actually the amplifier is part of a deal. He gave me two broken amps and a broken EQ. All he wants in return is one fixed amplifier (either one). The other amp is a Harman Kardon and the problem is not near as severe. I plan on fixing the BGW and returning it to him. Then the Harman Kardon is mine. Pretty sweet deal if you ask me. The EQ is probably going to have to be gutted, but that is not a problem. I can use the chassis for my own EQ.

As for how he broke it, I have no idea. His roommate told him that the amp started smelling like burnt plastic so he turned it off. My buddy just threw it in his closet and let the dust collect.

Apogee, I should've looked at BGW's website before. Thanks for the nudge. It seems that the whole module is replacable, I just hope that the price is reasonable. When I got to thinking about it though, I realized that actual replacable parts are harder and harder to find. Even if it costs more than I'd like, I may buy it to support their cause. I'll let you know how things turn out.

Thanks again,
Dan

promitheus 22nd July 2002 12:05 AM

It looks pretty burned to me.
I cant see how bad it is maybe its only smoked from one part burning.
You need to clean it on both sides with a good spray for PCB.
If the tracks are not so bad you can scrape the isolation off and rewire the thing again using the other channel.
If many parts are burned maybe its just to much work.

djsynthesize 26th July 2004 06:21 PM

BGW output module
 
The new output modules are available from RS sound, INC and their price is $268.00 each.

BGW went bankrupt last October and got bought out by a company called Amplifier Technologies. From what I understand, they are going to keep the production of the actual BGW amps, but they are going to call them The "new" BGW.

I have fixed boards like almost as bad as those in the past. I agree with Apogee. Check it out a little more, remember these amp are built like Tanks. You would be suprised how easy they are to work on.

Original Burnedfingers 27th July 2004 02:35 AM

Clean the board with some flux cleaner and a wire brush. I would guess the damage isn't as bad as it looks now. Fixable? Yes

djk 27th July 2004 06:52 AM

See that little teardrop tantalum next to the 3.9K resistor?

Used to be a pair where the crater is too.

The cap shorted, flamed out, and the resistor got caught too.

Replace everything, don't use tantalums.

I had to watch a saftey film at work a while back. They got one heck of a fireball out of a tantalum, they beat it out with a shop rag!


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