Hi,
I don’t know what a blinking amber light indicates but usually with electronics a good starting point is to measure the various power supply rails in the device to make sure that they’re all supplying the correct voltage.
Next is to visually examine the circuit board for any obvious component damage such as burnt out or heat stressed components and faulty capacitors, (leaking or domed).
Presumably the processor has tried to be reset by performing the reset procedure just in case this is what the blinking light might indicate?
Here’s how to do this:
''To reset the AVR's processor:''
1. Press the front-panel Standby/On switch for more than three seconds to turn the AVR off (the Power Indicator will turn amber).
2. Press and hold the front-panel Surround Modes button for at least 5 seconds until the RESET message appears on the front-panel Message Display
Here’s the [https://www.manualslib.com/manual/1618710/Harman-Kardon-Avr-151-230c.html#manual|service manual] for the receiver, It has schematics which should help although it appears that it is basically the CPU that does everything, but it is better than nothing.
Hopefully a start.