Check the PA collector/drain voltage (should be ~24V). Check the T/R relay function. Verify that the radio is not locked due to high VSWR.
Blown fuse, faulty power switch, or shorted transient voltage suppressor (TVS) diode. Samyung Srg-150 Dn Service Manual
Samyung SRG-150DN - Связь и Радионавигация Check the PA collector/drain voltage (should be ~24V)