Motorola Service Monitor R2600 R2660

[IFMATOS]

I just bought an Used Motorola Service Monitor R2660.  It works fine but the level of Spectrum Analyzer and Modulation Scope is too high.  With or without signal I can only see the botton of the wave foot.. DVM meausre OK, receiver, frequency OK, Sound, Generator. Can anyone give an idea of a probable cause ?  Thank you