As per title, I have a Cyrus smartpower that makes 'thump' when powering on or off heard through both speakers. This is occurs when the mains cable is plugged in, and the main switch at the back is turned on or off. There is a much quieter click when the front switch is pressed on, but not when off, which I can live with.
I have the service manual that shows the circcuit diagram but have to admit it is beyone me to where to start looking. I am planning to replace the electrolytic capacitors although none of them look bad (bulged or split). Examination of the board shows no damage e.g. burnt or discoloured resistors, components or pcb.
In the manual there is this - hence why I am looking to replace the capacitors.
Any help/advice appreciated.
I have the service manual that shows the circcuit diagram but have to admit it is beyone me to where to start looking. I am planning to replace the electrolytic capacitors although none of them look bad (bulged or split). Examination of the board shows no damage e.g. burnt or discoloured resistors, components or pcb.
In the manual there is this - hence why I am looking to replace the capacitors.
Any help/advice appreciated.
This thump, or pop, is often caused by massive inrush of current through the amplifier at startup. Could be caused by faulty caps at the power supply, or possibly that the amplifier was intended to operate at 110-115 VAC input, rather than today's 120-125 VAC here stateside. In either case identifying and replacing the power supply filter caps with proper ratings, may be your answer. Alternatively, your fix could be as simple as adding a properly rated thermistor to the hot line at the power switch, creating a light voltage drop and soft-start feature to keep the immediate power-on current low.
I've studied the circuit diagram a bit more and think I found the part that is the 'slow start' for the amplifier.
I am guessing this is done by the 2 transistor circuit in top left corner that turns on the constant current sources, outlined in blue, via CSS (in red) - is that correct?. Need to get the scope out to see what is going on.
I am guessing this is done by the 2 transistor circuit in top left corner that turns on the constant current sources, outlined in blue, via CSS (in red) - is that correct?. Need to get the scope out to see what is going on.