Akai AX80 – Every 8th voice dead
I have a problem with every 8th voice being dead on my Akai AX80. It varies what voices are dead. All the keys work. If I hold down one of the dead voices the rest of the keyboard is working just fine. It does not seem to be a pattern on what voices are dead. After a short pause in playing, a new set of every eight voice is dead.
• Akai AX80 V2 rev K (Tauntek)
To make sure it’s not one particular voice that’s dead try this:
Turn the keyboard on. Play 8 different keys and observe which voice didn’t sound. Then play 8 completely different keys elsewhere on the keyboard. Repeat the process always playing a different set of 8 keys than the last. Is there a pattern to it now or still random?
If I turn on the keyboard and play chromatically until I come to a dead voice (this initial note can be random) then every eight note chromatically from that initial dead note is also dead. So it follows a pattern. I also tested playing 8 random keys from that first dead voice. It is then the eight note that is dead. (It doesn’t have to follow chromatically)
The initial note being random is a confusing clue. This will probably take an oscilloscope to figure out. Good chance it’s something bad in the voice circuitry for one of the voices but the fact that the it’s random which note it starts with throws me off. Maybe the AX80 doesn’t always start with voice 1 as the first key played, but I’m not sure. With an oscilloscope you’d be able to check the inputs of each CEM3372 for an oscillation. Then confirm it passes to the output of each when a key is played. If the same CEM3372 is missing its input or output each time then it’s something in that voices’ circuit.
If you don’t have an oscilloscope I’d highly recommend taking this one to a tech, it’s going to take some pretty serious probing around to determine what exactly has failed.
Hi. Thanks for the input. I do hav an oscilloscope. I’ll try out your tips. Thanks.
Oh. I found out there is a pattern after all. When I power up the synth it is always the sixth note that is silent. And then it is every eight note after that.
Great, that’ll make it much easier to find. Probe the CEM3372 for voice 6, assuming the AX80 starts on voice 1 every time. Check the CEM3372 datasheet for the pin out. You should see oscillations at the channel inputs, pretty sure they’ll be there whether a key is pressed or not since the 3372 contains the VCA but I’m not totally sure on that for the AX80. You may have to tape or weigh 8 keys down while you probe.
If the 3372 has an oscillation at the input and nothing at the output then it’s probably bad. If the 3372s are socketed then you can switch them around to confirm. If the dead voice moves with the chip then that’s a bad 3372. If not then something else is bad in the voice circuit but it’s good to rule out the 3372. Comparing with a working voice is a helpful troubleshooting method to see how it should look.
Awesome! I’ll try to scope the CEM3372 for voice 6. Unfortunately they are not socketed. I’ll try first to resolder the pins just to be sure there is nothing wrong there.