Yamaha Montage 8 Repair

We recently had the pleasure of getting in a Yamaha Montage 8. The customer had complained that the left channel was louder than the right channel. We asked how they were using the instrument and what connections they had from the keyboard to their speaker system. Before diving into a keyboard repair, you always want to check and make sure connections are properly made and that the amplifier/speaker system you are plugging into is operational and not defective. It is a good idea to always have a spare amplifier to plug into and spare cables to try out, just in-case something is not working as it should.

Next, you want to check all output settings on the keyboard. Sometimes you might need to even need backup all the data on your keyboard and set the instrument back to factory settings. Once you look at all settings, connections, amplifiers, etc., and you are still having issues, that is when you dive into the keyboard and see what is going on. The first place to look at is the headphone port. We know that the L/R outputs are not working correctly, so we tested out the headphone ports to see if the left channel was louder then the right channel. This was proven to be true. Next, we pulled out our scope and probed the operational amplifiers following the digital to analog converters (aka DACs).

Once the proper connections were made, it was time to look at these operational amplifiers. It was found that the issue was coming from the operational amplifier positioned directly downstream from the DAC. The sound of a keyboard is created by the controllers interaction with a DAC. The DAC takes digital pulses and converts them to analog waveforms. The DAC then sends the waveforms through a series of operational amplifier circuits. These circuits filter, sum, buffer, and control the gain of the analog waveforms. The circuit in question was the summing and low pass filtering of the operational amplifier directly after the DAC. Figure 1. shows a similar circuit to the one encountered on this job. Once the issue was found we ordered a new AJK board directly from Yamaha. Once installed the keyboard outputs started working correctly again. The right channel produced as much volume as the left channel.

Lambert's Music Solutions | Op Amp LPF and Summing Circuit | Birmingham, AL Music Repair Shop

Figure 1. Op Amp LPF and Summing Circuit

Yamaha products are always fun to work on and Yamaha is always good about get parts sent to you quickly. If you have a Montage 8 and would like to get it repaired, give us a shout. Just fill out the form below to see how we can help.