20-03-2017, 01:48 AM
Looks like R18 will be the AVG bias resistor at 1 Megohm. I feel now I have a basic grasp of the circuit and am ready to "shock the world" with dynamic, shock and awe repair work. (Joking)
It is clear by now the 10.7 Megahertz IF is being amplified by ECH81. It is passing through the FM IF cans and being converted through the ratio detector circuit to audio. R12 is being bypassed so has no voltage for AM so the ECH81 Triode oscillator is idle. So no 455 KHz IF.
Best and safest bets: Mechanical fault in pushbutton mech, actual break in circuit in between the sandwiched waveband board (tab soldered to the PCB). Or sheer dirt. My plan is to see if I can get a lense under there.
Other sensible options as suggested is to use the tracks for clues. I have already carefully checked for broken wires but no harm in further checks.
Also the capacitors.
When doing voltage tests on my boat I have to be very careful. I have no test bench nor clamps. I use one arm and try to be aware. For certain that output transformer can kick like a mule.
It is clear by now the 10.7 Megahertz IF is being amplified by ECH81. It is passing through the FM IF cans and being converted through the ratio detector circuit to audio. R12 is being bypassed so has no voltage for AM so the ECH81 Triode oscillator is idle. So no 455 KHz IF.
Best and safest bets: Mechanical fault in pushbutton mech, actual break in circuit in between the sandwiched waveband board (tab soldered to the PCB). Or sheer dirt. My plan is to see if I can get a lense under there.
Other sensible options as suggested is to use the tracks for clues. I have already carefully checked for broken wires but no harm in further checks.
Also the capacitors.
When doing voltage tests on my boat I have to be very careful. I have no test bench nor clamps. I use one arm and try to be aware. For certain that output transformer can kick like a mule.
