MG966R servo - back and forth movement when PWM pulse width is 1500 microsecond

Just putting together a robot arm, and was setting all the servo motors to 90 degree positions (using an UNO board)..... mostly ok, except for 1 MG966R. The other three were fine. This odd-one-out did repetitive oscillatory motions.... maybe 5 degree forward then 5 degree back ...then forward then back etc.... continuously at a relatively quick rate.

I got capacitors for avoiding noise/glitch issues. Anybody else seen this kind of out of control issue?

I'm suspecting failed control circuity inside the MG966R plastic housing. Seems to be one of those luck of the draw things.

It's ok, as I happened to have a couple of spare servo of another brand.

Anyway, I opened up the MG966R and see a couple of 8 pin chips inside.... the green circuit board doesn't want to come out. Tempted to just brute force it (and probably rip whatever is connected to it on the other side heheheh). Anybody know if the board is supposed to just pop out for typical hobby servomotors? First time I opened one up heheh.

Update! I eventually figured out how to disassemble the servo (and even temporarily lost a gear pin after a gear dropped on the floor… but found the pin again hours later).

I found the problem. A bad solder joint meant either bad or no connection to one of the input (output) lines. The original soldering was poorly done - hence the cracking when the people at the factory were installing the board.

See the cracked joint in the photo.

The servo motor works fine now after a re-solder. Nice!!