That capacitor is part of the pitch control voltage circuit, which also includes the two 100k and one 470Ω resistors connected to pin 15, and the pitch control pot. The capacitor goes from the 470Ω to ground. If it’s not behaving as expected with the capacitor there it suggest there’s a problem either with the CV level or with bad or missing connections in the CV circuit. Measure the control voltages as described here, and if that looks okay, carefully check the components mentioned above and the connections between them. If those are all right, check also the components connecting to pins 1–3 and 12–14. It’s easy when breadboarding to get one of these connections wrong and the result is this kind of bad behavior… I should know, I’ve done it.
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