(ENGLISH) Saba MI-215 one channel broken.

HI! Sorry, I will ask my question in English.
I have fun with Mi-215 during half year, but yesterday one channel (left) stay silent.
When I turn balance knob to left channel - I hear sound from right channel. If no signal, I hear warm tiny noise in broken left channel. If signal exist, only weak distortion from broken channel.
I open cover and inspect. I substitute POWER amps - no fun. I substitute drivers - no effect. I measure voltage from input to linear amp (10V on both channels).
I suspect that problem somewhere in MID-BASS-TREBLE circuit. But I cant find.
I have no oscillograph, only digital multimeter.
When I set to MONO sometimes sound good from both channels. Sometimes only right channel.
Any opinions?

I even disassemble it, clean and check with separate PSU. It work.

Look like TDA1029 on commutation board is dead. Is it spare available now?

Yes, it was TDA 1029 (Ic1538). Replacing this chip keep amp alive.
Also I replace relay with new. And found new power switch in local bargain.
Great!

HI again. Is it available replacement for volume knob? There are tricky potentiometr with upper contact pair and long thin shaft. Ebay search got no luck.

Another little cosmetic trouble. Lamp on volumemeter burn out. Which replacement I can use? BL1703 not available. Maybe LED?

12v 2W as signed on shema. Small lamp with pair of wire from it.