Jx-3p sounds slightly off until it warms up

Hello synth nerds! Two voices (3 and 6) my JX-3p have a low pitched buzzing to them when I first power it on, and it takes about 10 to 20 minutes for it to fade away. I’m trying to refurbish this unit and recently replaced a few NAND chips on three channels (3,4,5) to get them working, but I assume this is not the cause. I’m wondering if anyone can give me some advice on where to search next. Could this sort of issue be caused by old capacitors or resistors warming up on channels 3 and 6? Or perhaps the oscillator chips? I’ve never heard of DCO synths needing time to settle.

Any advice appreciated.


Upon further investigation I think I’ve changed my diagnosis. What actually appears to be happening is that each voice has a low pitched drone when using the OSC 1 saw wave. The volume of this drone differs depending on the voice. When I first turn the Synth on, voice one and two are the worst, but once I play voice four it becomes the worst and voice 1 and 2 become normal. It’s seems like something is going wrong with the master clock? I imagine I’m going to have to get my hands on an oscilloscope to work this out, but if anybody could tell me if it’s worth checking capacitors that would be useful.