Question about Rotel RMB-1095 Power Amplifier
Im not sure how technical the kind assistance on this site is, but let me try. I should first mention that I do have electronics knowledge, but that is different to troubleshooting and repairing audio amplifiers particularly without a circuit diagram which is frustrating. My Rotel Amp has started distorting on just one channel with moderate listening volumes. At lower volumes there is no distortion. As the volumes increase so does the distortion, almost as if the Amp is clipping or the tweeter is faulty (but dont let this subjective info bias you !). The fault lies in the power amp, as with swapping the preamp to power amp cables the fault remains in the left channel. The same is true of swapping the speakers over, ie the fault remains in the left channel/speaker. Happily I can use the working Amp channel as a reference as a poor substitute for circuit diagram ! Assuming I can find my way around the board, my first port of call would be to check the power rails, although Im unclear how one channel can be fine and one not in this scenario. My next thought would be its a capacitor breaking down somewhere, which is going to be a little more tricky without a circuit diagram. Im wondering if any experienced wizards read this board and can help me out with some tips and experience, or failing that perhaps where to look for the same ? Terry.
I'd suspect that one of the two output transistors on that channel has gone bad. If you are unsure how to test or troubleshoot this, then you might try replace both the NPN and PNP outputs and catch the bad one that way. If your amp uses an output module then you would of course have to replace the module which would replace all the output transistors on both channels. Good luck. Another thing to look out for, is the emitter bias resistors. They are the large white ceramic ones near the outputs. Sometimes one of those will open up too. They will be of a very small resistance value like .5 ohms (point five ohms) or something in that general ballpark, and have a wattage value of typicaly 5 watts. So they are pretty big resistors. Be sure to check them all even if you do find a bad output transistor. They will often go out with the transistor. Good luck.
Posted on Jan 18, 2007
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