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 user manual online (unless you pay for it). It’s also quite old.
Most equipment that has a standby mode has a small low power power supply that is always on and powers some simple electronics to drive a mains relay.
The relay is used to switch the mains supply to the amplifiers main power supply.
This unit wasn’t switching the relay on, so no power was getting to the main processor board so something was wrong with the standby board. It had three open circuit transistors and a blown diode!
Replacing the failed components didn’t fix it. Nothings ever that simple!
I hard wired the transistor circuit to force the main power supply relay on. Unfortunately it switched off the instant it switched on.
After investigation with a scope it looks like something on the processor board was pulling the standby voltage down to such an extent that the main relay wasn’t getting enough power to keep it switched on. Little tip, if a relay clicks on it could just as easily have clicked immediately off again!
I found a circuit diagram for a similar mini hi-fi made by Denon that uses the same processor and associated components. Parts of the circuit look identical, and from that I should be able to find the fault, which I think is the processor not running in low power standby mode.
Some photos of the unit are below.
The small board below is the standby power supply with the main relay at the bottom left.
Bypassing the standby relay so mains gets to the main transformer brought the unit to life, although it takes 10 seconds before anything is displayed on the front info panel, so it’s quite a slow machine, or there is another problem with it!
The photo shows the main transformer and CPU board. The power supply electronics is on a board under this one.
As I’m fixing it for myself it’s more of a challenge than anything else so I’m not too worried about the amount of time it takes, although it could easily end up in the spare parts box!
If anybody has a circuit diagram they want to chuck in my direction let know.
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