Help needed in repair of a solid state bass amp circuit board

[tsunamijesus]

Hey all,
I am a novice electronics maintenance tech, worked as my university's tech supervisor, but I never had to do much for components swapping. I just bought a JMF Spectra HB160 for cheeaaap but upon plugging it in I was disappointed to find that it clearly has something wrong. After pulling the chassis I found this pretty obviously fried bugger.


I think it's the R14 because it is in series with the speaker jacks' positive lead. Curiously, there are two jacks, it isn't labelled which is the primary, and the second jack doesn't have a ground. So I am wondering if I plugged into the wrong jack? Also, it's labelled for 8ohm output, but I wasn't terribly reverent of that and plugged it into a PA main that I remember as being 8ohms but may have been 16. That wouldn't totally fry it would it?

I can't really read the board too well and the spot it burnt up looks like an important portion of the circuit. This component (presumably a resistor, but not confident) is the largest of these types of components, but it's too burnt to read the code.

Help? I'm sure this is incredibly basic for anyone who has ever done anything in this field but I have only built with the aid of layout schemes, and my repair skills seem to have atrophied from a state of earlier competence. Any help is greatly appreciated.

[isaac42]

First, yes, it's a resistor. It's probably labeled on the bottom of the circuit board. You're going to have to pull the board to replace it, anyway.

The real question is, why did it burn out? Placing a 16 ohm load on the amp would not have done it, and the output jacks are almost surely in parallel, so there wouldn't be a primary output jack. They'd be equivalent.

So, replace the resistor. Resistors are cheap, even half watt resistors, as this appears to be. You say you think it's R14. Sounds as though you have a schematic. That should make things easier. There's a possibility that the resistor was bad, or that a one time event caused it to burn out. If that's the case, then you'll be fine. More likely, in my mind, is that there is something else wrong that caused the resistor to blow, and it will blow again. Then you get into the real troubleshooting. Good luck.

[isaac42]

Oh, and a fine pint of nomenclature. In my training, this is called component replacement, not circuit board repair. Circuit board repair is fixing problems on the board itself, such as broken traces or lifted pads. I've even repaired an actual broken board.