Synthesizers

I'll start by saying that I'm new to synthesizers and not really musically inclined...

I have a Behringer Neutron that I purchased second-hand and it seems like the oscillators flutter and go a little sharp/flat as they play. The fluttering happens pretty quickly so even during a short key press it sounds like the note is going into and out of tune repeatedly. It's not really rythmic, just kind of random fluttering that makes all of the notes sound kind of bad.

To rule out any of the other parts of the synth I grab the OSC1 (or OSC2, both behave poorly) output directly and play through an amp. I have the LFO rate dialed down, although I don't think that should have an impact given that I'm listening right at OSC1. The noise is dialed down, both attenuators are at minimum, but again, I don't think those should have an impact because they are being skipped since I'm listening at the OSC1 output directly. All of the different octave ranges have the same behaviour.

When I enter tune mode (by holding the corresponding OSC 'Range' button and watching the LEDs around the LFO shape knob) and adjust the OSC1 tuning knob I can never get just the center LED lit showing it's in tune. The closest I can get is the center mostly lit and the two adjacent LEDs flutter like the pitch does so you can even see what I'm hearing on the built-in tuner.

An additional indicator that something is wrong is that it takes anywhere from 7 to 15 minutes to go through it's calibration routine whenever it is powered on. In other words, it's sits with the LEDs around the LFO shape knob going back and forth and the octave LEDs ever-so-slowly advancing.

Does anyone have any experience troubleshooting something like this? I'm not really sure where to go from here.

Thanks,