What causes noisy "bitcrush" decays in earlier digital synths?

Hello. I would like to know what is a common cause for early digital synths (like Roland D-50, Yamaha SY-22, etc.) to exhibit a bitcrushing noise sound as the sounds decay. I imagine they all do it to some extent, but I’ve played some units where it becomes annoyingly loud. I’ve read about things like DAC and muting transistors in the past. What’s usually going on and can anything be done in bad cases? Thanks.

The D-50 reverb definitely has a very low bit depth sound, even the D-50 VSTi captures that faithfully. It’s fairly audible on the reverb tail of some patches. Maybe you could provide a reference recording of your unit (preferably of a preset patch for easy cross-checking) to check if the noise is really louder than it should be?

Thanks for your reply. I’m not just talking about the D-50. I don’t have a sample readily available, but I’ve heard this kind of effect on things like the Yamaha SY-22, Roland D-50, Roland JD-990, and I’m sure others. The sound gets quiet, almost nothing, then starts crackling like a bitcrusher was applied to it, so it gets a bit louder right as it fades. On the JD-990, there is a trimmer to calibrate the DAC, but this uncalibrated sound is what I will hear on other digital synths as I mention above. So I am wondering if these synths have DAC problems or other circuits going bad.