Yamaha M-70 Repair And Restoration

This Yamaha M-70 Power Amplifier is in need of some service.

I have removed the top cover of this Yamaha M-70. The amplifier is constructed well.

I'll remove the faceplate for cleaning. After removing six screws you need to unsnap the power lamp from the faceplate. 

There are two LED's on the left channels power level indicator that are not working.

I will have to do some disassembly to work on the LED issue that this Yamaha M-70 power amplifier has.

 I will cover any areas where any accidental cosmetic damage could occur.

 There are several small plastic pins that must be removed. If you can't pull them out with your fingers a small screwdriver will help.

Once the pins are removed you are able to remove the protective cover from the LED assembly of this Yamaha M-70.

I'm getting closer to the LED's but there is more to remove. Any vintage stereo repair or restoration takes some disassembly.

After removing three lamps from the back I'm getting closer. Be very careful when you remove the lamps. They or the wires break easily. 

I can now get to and  remove the LED cover. This cover is fitted into the LED assembly and will come loose if you slowly move it side to side.  

I can now get access to the LED's and their associated circuitry to troubleshoot the LED issue with this Yamaha M-70 power amplifier.  

I'll use a signal generator so that I easily turn the LED's on and off.

The sixth and the ninth LED's from the bottom are not operating.

After troubleshooting the issue I found a defective IC. IC505 was the reason for the two LED's not working.

I was able to find a NOS Toshiba TA7612AP IC to get the meters working properly in this Yamaha M-70.

After replacing the defective IC each LED lights up as it should in this Yamaha M-70 power amplifier.

I have the faceplate back on and I'll do a little bench testing before I put the M-70 totally back together.

All is well on the test bench. This Yamaha M-70 repair and restoration is complete. It's time for some music!