I acquired a Yamaha CRX-D430 mini HiFi to repair, fault being it won’t switch on.
Those sort of faults usually fall into a couple of categories. It’s either detected some sort of over current situation or over heating that has triggered the CPU into shutting the unit down.
This one didn’t do anything, not even a relay click.
Unfortunately this unit appears to be one of those that only has the service manual online (unless you pay for it). It’s also quite old.
If you don’t know what you’re doing don’t ever go poking around inside amplifiers with them plugged into the mains supply. If it’s plugged in, 240v ac (115v in the USA) is usually present somewhere in the unit even with it switched off. Also the main amplifier stage in powerful amplifiers often runs at voltages above 50v which can give you a shock.
Standby Circuit
Most equipment that has a standby mode has a small low power supply that’s always on and powers some simple electronics to drive a mains relay.
The relay is used to switch the mains to the amplifiers main power supply. On some units the amplifiers CPU might be put into an ultra low power mode and then powered from the standby supply. This enables it to monitor the units power switch so it can be switched back on again.
This unit wasn’t switching the mains relay on, so no power was getting to the main processor board so something was wrong with the standby board.
It had a blown diode.
Some photos of the unit are below.
The small board below below is the standby power supply with the mains relay at the bottom left.
The photo below shows the main transformer and CPU board. The power supply electronics is on a board under this one.
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