Yamaha RX-360 Backlight

In my gaming room I have "old faithful" which is a 30 year old Yamaha RX-360 Natural Sound Stereo Receiver. I use it for my CD Player, Turntable and gaming PC. I moved the amplifier a bit and the backlight for the display went off, I thought to myself that it was the end, a very sad moment. However, I did a little research and found out that it was probably just a tiny incandescant bulb that had failed, so I decided to replace it with one of the 5mm LEDs from the Arduino kit, which would require a bit of math and a modicom of soldering.

Taking the top of the case off showed the circuit board and the transformer, the voltage to the 4mm bulb was 14.4V and I did some research and the expected current required was 70mA. I removed the bulb and it was in bad shape, in fact the soldered contacts were deteriorated and broken. The bulb is shown here encased in a rubber grommit, but one contact was detached, and the second contact broke very quickly when I extracted the bulb.

I used a bread board to check out my LED fix, worked out a suitable resistor value using the magic formula of electrical loveliness and played about with a couple of resistors to obtain a suitable dimness. I am sure you will want to know the magic formula, and it went something like this : R = (V-Vf)/If and V being supply voltage 14.4V and forward voltage for the LED, Vf is 2.0V and then the forward current taken as 0.03 or 30mA. That gave me a value of 413 ohms for the resistor, but I decided to use a 1k resistor so the LED would be dimmer and perhaps last forever. It can be an exact science, but in this case, who dares wins.

It was then just a case of soldering the components to the power lines, using a little heat shrink and tape to keep things separate and safe. I was quite pleased that it was a tidy job and all that was left was to use the existing grommit and reinstall. I must admit that I am really quite crap at soldering, my hands shake, my eyesight is poor, even with reading glasses on, and I always feel the need to have at least one extra set of hands when doing something like this. You may notice that I did not put any tape, or heat shrink over the resistor, mainly as it may get a little hot under normal operation, I am sure there is another calculation to work the thermals out.

The resulting backlight is at a great level for my dark gaming room, and the entire process took about an hour, and I believe that this old brain learned a few new tricks in the process and I was suitably impressed with myself to want to show off again on the interweb here on the blog. The amplifier is reinstalled in my room and working fine. Happy days indeed and no money was spent.