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Thread: Roland KC-350 Woes. Low, distorted output.

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    Roland KC-350 Woes. Low, distorted output.

    Hey guys,

    I've got a Roland KC-350 that's got me stumped. It's output transistors shorted out, and with them took the horn, as well as fuses 4 and 5 (100mA mini), C26 and C27 (.068uf) and R41 (27 ohm). I replaced all known bad components, including the output transistors, but all i'm getting is a weak, distorted signal on both the horn and 12".

    It seems like maybe the outputs aren't biased properly. I'm getting B= 0.7 C= -52.9 E= 0.7 at Q17 2SA1962, and B= 0.7 C= 52.3 E= 1.3 at Q7 2SC5242. Anything jump out at anyone?

    Roland KC-350UC, 550UC (2003) Keyboard Amp Service Manual.pdf

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    Q17 has no bias and Q7 is reverse biased if your readings are correct. There's also likely some DC on the output, so I'd disconnect the speakers until you get it figured out and while you work on it. Check driver transistors and associated resistors including emitter resistors.

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