I recently watched this video    • Fixing the MHS-5200A   by devttys0 and decided to try it on my own 24MHz FeelTech FY3200S.

The problem is that at high frequencies (greater than around 15MHz) the final stage op-amps are unable to produce the requested Vpp so I decided to replace them. According to devttys0 this is because the original parts lack the required slew rate.

On investigating my own function generator, I discovered that these op-amps had fake part numbers on them so I was unable to determine what they originally where. I replaced them anyway with genuine TI THS3092 parts and the Vpp now remains correct all the way up to 24MHz.