(AI translated, original post from 2022.06.02)
Groundhog Day radio. Well, not quite, the original is the Panasonic RC-6025, but mine is a Sanyo Sterocast RM5320, probably manufactured in 1972 (it could also be under another brand, such as Siemens alpha). Definitely Japanese, as it says “made in Japan” everywhere, on the speaker it says Sanyo and similar.
Why do I know there are other brands? Because the first radio I bought was Siemens. But not only did it have a damaged motor (a plastic gear without teeth), it also got pretty badly damaged – the plastic of the 70s is very brittle.
The clock mechanism is completely fine, but the motor is not. By the way, each full hour has the “JAPAN” inscription.
(the black electrolytic is already mine – 3300µF really helped with the humming. Who sees the screw? :).
The radio hummed a lot because the main capacitor, also Sanyo, instead of 2200µF has maybe 20µF, and not always that. I replaced the capacitor and the radio died. And here’s this “old school” situation that’s scary. A whole mountain of parts, everything chaotically connected. So I took the radio from another one. The next day I started analyzing it and noticed that something is seriously grounding the power supply. I found a large resistor which theoretically formed a “buzzer” signal – as far as I understand, a 50Hz signal is taken from the transformer and passed to the speaker. I don’t know why it was shorting there, so I didn’t speculate too much and removed that resistor. And the radio works again… but I already reassembled everything from one case to another. I got annoyed. Because the insides of the other radio are somewhat fancier, there is some option to connect a “stereo decoder” (whatever that is).
The PCB technology is really interesting. The bottom side is standard copper traces. The PCB itself is made of getinax. But the top side is something terrible – the top traces are drawn with conductive paint (probably silver lacquer) and there are even “drawn” resistors. If you damage anything there, it’s a death sentence for the board. Then it’s probably easier to reconstruct the radio with a new PCB from scratch.
