Jupiter 6 - Arpeggio RATE pot not working


I have a Jupiter 6 that has an issue with rate knob. It doesnt change the speed of the arpeggio. The pot works with the wiper moving between 0V-5V, but no changes in clock speed. I dont have anything going into the Arp Clock jack. Any ideas what I should check?

Left hand panel board, connection to IC1 pin 7 from arp rate pot wiper. All the controls are multiplexed and will show up at IC2 pin 1. But you need a scope to see the waveform, as you move the controls the waveform will change.

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Thanks! I was able to trace that on the scope before, and I’m seeing changes to the waveform - it’s like a sample and hold waveform with a level that changes as you turn the Rate knob. So that’s working there but something after it is not working. I looked on the schematics and think I saw where the signal hits the CPU board. But not sure what to check from there on. I’m out of town for a couple days and can get back to it then…

What the…?

Why would someone change the internal clock to XTAL1 instead of XTAL2 as stated in the schematics? Thats Pin 18 and 19 on the 8053 (in this synths case a 89C51)? And the other red jumper you see is going to Pin 10 on the LS04 (IC20). Is there any reason for this?

Could this be the reason im not able to adjust the Arpeggio clock speed? It’s running at one speed and the RATE knob doesn’t change anything.


Just discovered this has the Europa mod installed! The main CPU chip did not specify. It was set to midi clock mode and that disables the Rate knob. Switched it to internal clock sync and it started working.

I was searching for pictures of the CPU board online to check about those traces and came across the manual which does this exact mod.