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Help with Handclap Issue (constant noise on output)

Posted: Jan 11th, '24, 21:35
by JimAudio
The handclap has always sounded a bit dark on my Nava without much attack. I fried one of the sequencer/trigger chips a while back which I've repaired, but the handclap now emits a constant noise after it's been on for a while. I'm assuming a VCA or transistor is not functioning properly, but I'm uncertain which one. The Roland schematics show 2 VCAs - Q37 & IC30 (the BA662/6110).

I'm hoping someone can help to diagnose the issue or offer any useful voltage references to compare with my unit!

The BA6110 has a constant -13V at the control input (pin 4) and constant noise at it's output. Above this, Q38 has -5V on one base and -4.8V on another (TM1 side). R235 above has -7V on the Q38 side and +0.8V on the IC26 side.

The envelope seems to be working correctly at the base of Q37 (+8V after D52, +2.8V after R233, +0.5V after R234).

My thought is BA6110 is working ok and maybe the control voltage coming into it is incorrect?

Any advice would be appreciated, thanks!

Reposting parts of the schematics below: ... aasax&dl=0 ... 978ka&dl=0 ... bbphw&dl=0