03-11-2023, 05:21 AM
+1 on Arron's comments, something is wrong with the oscillator tanlk circuit. The oscillator seems to be running at a much higher frequency than it should be. This is kind of a stumper. A few things to look for (IMHO, and I do mean humble)
Does either the oscillator coil or the main tuning cap look like it was replaced? Is the tuning cap Osc section the same size as the RF section? (The older ones were, the newer ones have smaller plate on the oscillator section
If you have a digital all band radio like a Sangian or a Grundig, use it to validate the signal generator.
If memory serves, the local oscillator should be at 465 KHz above the desired frequency. Calibrate the tuning dial (With cap fully meshed, set the pointer to 535KHz, with cap fully meshed, scale should read 1650 KHz (or whatever the highest broadcast frequency is). Tune the radio to a known station on the lower end of the scale. Use your digital radio to test for the frequency of the local oscillator. tuning the digital radio, it should squeal, then get quiet at 465 KHz above the frequency tuned on the Coronado. My guess is that you will find something to be way off.
More to the puzzle:
Nost adjustments to RF, IF and Local Osc allow only minor adjustment. For example, if the IF Frequency is 465 KHz, you shouldn't be able to adjust both primary and secondary of both IF Xformers to resonate at 200 Khz. If the oscillator is running at 1000KHz higher than it should, you should not be able to adjust RF resonance to correct for this much difference.
Does either the oscillator coil or the main tuning cap look like it was replaced? Is the tuning cap Osc section the same size as the RF section? (The older ones were, the newer ones have smaller plate on the oscillator section
If you have a digital all band radio like a Sangian or a Grundig, use it to validate the signal generator.
If memory serves, the local oscillator should be at 465 KHz above the desired frequency. Calibrate the tuning dial (With cap fully meshed, set the pointer to 535KHz, with cap fully meshed, scale should read 1650 KHz (or whatever the highest broadcast frequency is). Tune the radio to a known station on the lower end of the scale. Use your digital radio to test for the frequency of the local oscillator. tuning the digital radio, it should squeal, then get quiet at 465 KHz above the frequency tuned on the Coronado. My guess is that you will find something to be way off.
More to the puzzle:
Nost adjustments to RF, IF and Local Osc allow only minor adjustment. For example, if the IF Frequency is 465 KHz, you shouldn't be able to adjust both primary and secondary of both IF Xformers to resonate at 200 Khz. If the oscillator is running at 1000KHz higher than it should, you should not be able to adjust RF resonance to correct for this much difference.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
Best Regards,
MrFixr55
