Hi Guys, the unit has always sound on radio, but only sound from tape if i use a external power supply batteries are fine - around 1.6 V Even with power supply i only have 2V on the 3V Testpoint Q805 i got 0.55V not 2.8V with external 2V poer supply i have 2V could it be Q805 is defective ? Many thanks for your time
Since only head preamp and Dolby amp are operating on 2.8V, it makes sense the radio works without this voltage rail. Would rather suspect C901 (inside the sidecar) than Q805. This capacitor is needed for the DC-DC to properly start.
Thanks for your help. I ordered the 1500uF already today. when I connect a battery directly to the 2 DC pins on Unit side without battery case - my try to test if the C901 is defective - but same result I measured the cap - it was around 1.9 mF is the cap needed or should it work if i connected the battery ? i understood the cap as a buffer ?
I mistaken this model with another one. C901 is not needed (it's there for filtering mains hum of AC adapter), as there is another capacitor at the input (C312). Start by measuring voltages on the schematic. Do you get battery voltage at input of DC-DC (emitter of Q802) ? Do you get the 1.25V at base of Q805 ?
