Yamaha CS-5 synthesizer fix

I’ve always been a fan of old Yamaha gear. They did put out some amazing stuff in the late seventies and early eighties, including the amazing SG-2000 electric guitar, the CS-80 polyphonic analog synthesizer, they pioneered FM synthesis with their DX line and made it popular with the DX-7. I’ve already mentioned their pedals in previous posts. I love them.

One item that I got in a trade and knew nothing about was the Yamaha CS-5 monophonic analog synthesizer.

Looking for more information about it on the web, I learned that Yamaha (which like most Japanese corporations – deal with several non related industries all at once), also put out a motorcycle with the very same model name!

Another object of desire with no less appeal..

Anyhow, this was quite different than the Roland SH-101 I was so used to at the time (and the only reference I owned at that point). Very basic monophonic, but unlike the SH-101 which has an amazing Low Pass filter, this thing has a variable filter with audio input and an LFO that goes well into AM territory. Combined with the CS-5 VCO, the LPF mode is thinner in comparison with the SH-101, but the BPF is great to have, and the HPF mode is excellent! Actually, that’s what I find this synth most effective for – piercing ears.

A few years ago the synth stopped working. Well, not exactly.. When switched on it would stick on one note and refuse to obey the keyboard. At first I thought this would be a relatively easy fix as I suspected the problem was a sticky key contact. Not so.. testing the keyboard proved that all the keys are fine.

Searching the web for a schematic or service manual didn’t help. Apart from a funny user manual there was no technical information to be found anywhere on the web. The closest thing I found was a service manual for the CS-15. It wasn’t until I discovered this post that I started suspecting the problem might actually be in the 4016 key assigner IC. The 4016 IC is very cheap and easily obtainable, so I took a chance and replaced it.


Now two things come to mind:

1. The synthesizer sounds good but is very limited!

2. I can see at least 10 spots where new knobs would fit in nicely!

Just thinking…


(I didn’t make a video demo of the CS-5 since there is A LOT on YouTube already. Here is one I chose because I like the dude’s shirt & background globe, plus he’s putting out some awesome stuff through that badly matched Fender guitar amp!)