Post by serafis on Sept 26, 2023 4:06:36 GMT -5
Hi, I'm trying to repair a Yamaha RX-V675 that won't power on. Service manual is at www.manualslib.com/manual/1233924/Yamaha-Rx-V675.html
The problem seems to be with the 5.6V rail from the switch mode power supply. It measures just over 5.5V but isn't stable, dropping to as low as 3.2V apparently randomly. Sometimes the unit will briefly turn on and, on one occasion, I was able to get to the diagnostics which showed "PS-PRT3-131L" which means protect mode because the 5.6V line is low.
The power supply looks like a fairly standard switch mode circuit, with the 5.6V line coming from the secondary of the switching transformer via a dual common-cathode schottky diode and a number of electrolytic capacitors. All of these test OK as far as I can tell. With the supply disconnected from the rest of the receiver, the 5.6V rail is stable at just over 5.5V, but as soon as it is connected to the rest of the receiver it becomes unstable.
The power supply board shows signs of overheating around R3737, R3738 and R3739 near the primary of the switching transformer. Not sure what would be causing that.
If I piggy-back my bench supply, set to 5.6V, across the 5.6V rail, the unit powers on fine and appears to work normally (although I haven't tested everything in this mode yet). The bench supply shows a current draw of 0.19A when in standby and around 1.4A when powered on. So it appears that the receiver's power supply isn't delivering the required current and that is why it won't power on.
I'm a bit stumped as to what to check next so any help gratefully received.
The problem seems to be with the 5.6V rail from the switch mode power supply. It measures just over 5.5V but isn't stable, dropping to as low as 3.2V apparently randomly. Sometimes the unit will briefly turn on and, on one occasion, I was able to get to the diagnostics which showed "PS-PRT3-131L" which means protect mode because the 5.6V line is low.
The power supply looks like a fairly standard switch mode circuit, with the 5.6V line coming from the secondary of the switching transformer via a dual common-cathode schottky diode and a number of electrolytic capacitors. All of these test OK as far as I can tell. With the supply disconnected from the rest of the receiver, the 5.6V rail is stable at just over 5.5V, but as soon as it is connected to the rest of the receiver it becomes unstable.
The power supply board shows signs of overheating around R3737, R3738 and R3739 near the primary of the switching transformer. Not sure what would be causing that.
If I piggy-back my bench supply, set to 5.6V, across the 5.6V rail, the unit powers on fine and appears to work normally (although I haven't tested everything in this mode yet). The bench supply shows a current draw of 0.19A when in standby and around 1.4A when powered on. So it appears that the receiver's power supply isn't delivering the required current and that is why it won't power on.
I'm a bit stumped as to what to check next so any help gratefully received.
