06-14-2020, 04:21 PM
Hi,
I studied the new schematic and first of all I learned that this radio is a dual band : broadcast and SW and the other position of the band selector is to enable the external Pad stations.
Starting from the end The radio now is working pretty well on Broadcast, but not at all on SW. I changed the two capacitors number 5 and 10. I had some trouble because on the schematic the number 10 is 50pF and installed there was 100pF and the number 5 on schematic is 5pF but installed and 80pF. Is it possible an error on the schematic for the 5pF ?
The radio seems to be repaired many years ago with old component, but newer than the other. The radio finally worked on broadcast changing them with two mica capacitors of 50pF each.
But I have a lot of doubts about the voltages and a question : why the radio started to work on Broadcast when I changed capacitors on the SW Aerial Transformer? At least this is what I understood with my limited competences looking at the schematic
Starting from the Voltages these are my readings from B- (the electrolytic negative Pin) for each measure:
35Z3GY PIN 7 132.9 VDC
50L6GT Pin 4 99.7 VDC Pin 3 87.6 VDC
7C6 PIN 2 62.9 VDC ( The schematics says 28vdc)
7B7 PIN 3 60 VDC PIN 2 98.7
7B7 PIN 3 60 VDC PIN 2 98.7
XXD PIN 3 Starts at 71 VDC and stabilize at 56 VDC Pin 6 83 VDC
I also verified again the two 10K resistors 22 and 26 with the DMM and they are ok. The voltage and is 99.8 VDC between the two and became 56 VDC after the resistor 22 . I also tried just to see what happens to change the resistor 22 with an 8K and a 2.2K ohm . The voltage on pin 3 increase. I installed again the original 10K resistor checking again the resistance and the voltage.
Next week will arrive the 22 uF Electrolytic and a new 4.7M ohm 2W resistor I used temporary a 0.7W. I will try to verify again the voltages
I didn't discovered why the voltage is so high on the 7C6 ( 63V Vs. 28V) any idea?
What do you suggest to start troubleshoot the SW band?
Thanks
Camillo
I studied the new schematic and first of all I learned that this radio is a dual band : broadcast and SW and the other position of the band selector is to enable the external Pad stations.
Starting from the end The radio now is working pretty well on Broadcast, but not at all on SW. I changed the two capacitors number 5 and 10. I had some trouble because on the schematic the number 10 is 50pF and installed there was 100pF and the number 5 on schematic is 5pF but installed and 80pF. Is it possible an error on the schematic for the 5pF ?
The radio seems to be repaired many years ago with old component, but newer than the other. The radio finally worked on broadcast changing them with two mica capacitors of 50pF each.
But I have a lot of doubts about the voltages and a question : why the radio started to work on Broadcast when I changed capacitors on the SW Aerial Transformer? At least this is what I understood with my limited competences looking at the schematic
Starting from the Voltages these are my readings from B- (the electrolytic negative Pin) for each measure:
35Z3GY PIN 7 132.9 VDC
50L6GT Pin 4 99.7 VDC Pin 3 87.6 VDC
7C6 PIN 2 62.9 VDC ( The schematics says 28vdc)
7B7 PIN 3 60 VDC PIN 2 98.7
7B7 PIN 3 60 VDC PIN 2 98.7
XXD PIN 3 Starts at 71 VDC and stabilize at 56 VDC Pin 6 83 VDC
I also verified again the two 10K resistors 22 and 26 with the DMM and they are ok. The voltage and is 99.8 VDC between the two and became 56 VDC after the resistor 22 . I also tried just to see what happens to change the resistor 22 with an 8K and a 2.2K ohm . The voltage on pin 3 increase. I installed again the original 10K resistor checking again the resistance and the voltage.
Next week will arrive the 22 uF Electrolytic and a new 4.7M ohm 2W resistor I used temporary a 0.7W. I will try to verify again the voltages
I didn't discovered why the voltage is so high on the 7C6 ( 63V Vs. 28V) any idea?
What do you suggest to start troubleshoot the SW band?
Thanks
Camillo
