PINN is predicting trivial solution for stiff ODE [D]

I am learning physics informed neural networks. Currently, I am solving a simple second ODE (damped harmonic oscillator). The equation is m*d2y/dt2 + mu*dy/dt + k*y = 0 (bcs: y(t=0) = 1, y'(t=0) = 0). I managed to draft a code. The code works for k values upto 50. However, when increased the value beyond 50, PINN is predicting trivial solution. I tried several things: reducing the learning rate, increasing the data points, reusing the weights trained using lower k values, and using a for loop to increase the k value in smaller steps (step size 20). However, none of them helped. Could you help me with this. Thanks in advance.