Vintage SONY STR-6046A Amplifier. VGC. FM problem

Im selling really nice looking Vintage receiver made in Japan. All cleaned, new led lights all works pefect except FM radio. After turned ON, FM works perfect in Stereo, but for 10-15mins only. Then loosing signal. If you turn Off and wait few mins, singal will back. Im not able to fix it. Anyway, Amplifier works pefect and can be use with Turntable or any aux input. Prices of fully working are around €230-250. So I think my price is fair. Shipping no problem. Some specs: Tuning range: FM, MW Power output: 20 watts per channel into 8Ω (stereo) Frequency response: 30Hz to 40kHz Total harmonic distortion: 0.8% Input sensitivity: 2mV (mic), 2.5mV (MM), 250mV (line) Signal to noise ratio: 60dB (mic), 60dB (MM), 70dB (line) Output: 250mV (line), 30mV (DIN) Dimensions: 434 x 144 x 345mm Weight: 9kg Year: 1971