Why are the power transistors running hot?

I've recently got a Roland cube 60 Keyboard amplifier.

Basically I've give it a little refurbish and got it working, but I can't find the schematic anywhere at all for the Keyboard version, only the bass or guitar amps.

It's an old one, not one of the new ones.

My power transistors are running hot, I'm just wondering does anyone have any advice or does anyone have a schematic for this thing?

Thanks guys


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There's not much difference between the various versions of the old Cube 60, and the power amplifier (which is what you're looking at) is most likely identical between them.

If your power transistors run hot, their bias setting is off. The bias on this amp is non-adjustable, you'll want to inspect D1, D2, D3, Q9, Q10 and associated components. With the amp idle, you'll want approx 3 - 5 mV across the power transistor emitter resistors, disconnect the speaker when you make this test.

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Thanks man, I'm gonna check the bias and then go about checking the components, I'll let you know what happens! Great advice.


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