I’m continuing to work on this Grunow 589 radio, and it’s being difficult. If you’re just joining in, take a look at the previous entries to see what you’ve missed and catch up – not to mention, there are some interesting photos.
Part 1: Identification and Task List
Part 2: Intake Checks
Part 3: Capacitor Replacement
Part 4: Resistors and Controls
Part 5: First Power-Up
Part 6: Socket Replacement and First Alignment
Part 6.5: Diagnosing an RF Intermittent
Part 7: Conclusion
I’m attempting to diagnose an intermittent in the RF stages of this radio. I’ve not yet tracked it down, but I thought a photo of my workbench with all of the really interesting test equipment would be worth posting:
Left to right, EICO 324 signal generator, Victor frequency counter, HP 200CD test oscillator (not used in this step but will be later), generic digital multimeter, and my EICO 460 oscilloscope.
I’ve attached the oscilloscope to the volume control to watch the waveform. Since the volume control is after the detector, the scope is measuring the output of the RF stage which is helpful for seeing what’s going wrong.
Update on 6/24: It turns out the problem was caused by a brittle wire that broke under its insulation. The break wasn’t visible, but was located when touching a certain wire changed the set’s behavior. After repairing the break, the problem appears to have been resolved.