Yamaha RX-V390

Discussion in 'The Projects Forum' started by FelixAUS, Feb 16, 2014.

  1. FelixAUS

    Thread Starter New Member

    Feb 16, 2014

    I have recently acquired an RX-V390 Receiver which will turn on fine however off again after ~3 seconds (even with nothing connected to the receiver).

    From what I have read about, Yamaha have some short circuit detection circuitry which allows for the main chip to detect shorts and shut the power relay off.

    My initial thought was it was probably a blown cap somewhere; however after inspection of them all they all look fine. I have disassembled and removed the input, tuner and surround (rear/centre) PCB's, so all that remains is the front control PCB (with the control IC), the power supply and the main power amplifier board. (See photos).

    My question is, where to from here? Does anyone know how this short detection works on these receivers? (or on others for that matter).

    I have noted the pins PROTEC and PWRLY on the IC, so I assume PROTEC isn't getting the required signal and is shutting down the power relay.

    I think if I can understand how this short protection circuit works then I may be able to narrow down which caps/transistors to replace or further inspect, as nothing is obviously damaged under visual inspection.

    Also, does anyone have any good references to checking caps/transistors/amps that may help me? (I have a multimeter and DSO)

    I know this write up is quite vague, however I'm at a bit of a loss as to where to continue with it so any help is appreciated! I can attach the service manual with the circuit layouts if anyone is interested?