Quote:
Originally Posted by bob91343
The problem is either in the V4 circuit or the FM detector. Check those germanium diodes, the OA-70s. Replace with something like 1N270 or other germanium if they aren't good. Also the detector transformer might have a problem, like misalignment or even a bad internal capacitor.
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Your advice is much appreciated, thank you for following the thread - will do exactly that tonight. Is it common for Ge diodes to fail? I will check them with a digital multi meter, diode test function, is that an adequate test for small signal diodes? I could also use the EICO 667 to check them, I suppose.
I acquired a B&K 415 sweep marker generator some time ago, but have never used it. Am thinking towards setting it up and checking the IF bandpass and ratio detector S curve (youtube has some awesome videos by current and former VK members), but having never done that type of work before and not knowing the condition of the B&K I want to approach it with caution - definitely don't want to make things worse!
Just so you know who you are talking to, I would say my skill level is moderate, I am an electrical engineer, but focus on power systems and not electronics professionally. From a hobby perspective I have done a lot of work with building and repairing tube and solid state audio and guitar amplifiers, and have been poking around with old televisions for a while. I've also aligned and restored antique AM radios, but IF and RF work at higher frequencies (such as an FM radio) is kind of new ground for me, so I really do appreciate the guidance from experienced people. I do plan to replace all the electrolytic capacitors in this radio, but would like to make it work first, and then do preventive maintenance, so I don't end up introducing a new problem which makes the existing one even harder to find.
As for the neon indicator, it must just be bad, it lights up and then goes off, but the voltage does not fall below 100 at the socket base in any case. The lamp is the size of a 47, but with a screw base rather than a bayonet.