@dreye throwing stuff out is not an option. Let's investigate.You mentioned testing it with a 3V AC DC adapter. Is that what you have checked? What else have you looked at. Use this guide [guide|111640] to tear it down. Then take a couple of good pictures and post those with your Question. Lets see if we can identify any issues. Your Monotron will work with 3 V but it uses a boost circuit that brings the voltage to 5V. I would start with the boost circuit and check IC1 TPS61071
@dreye throwing stuff out is not an option. Let's investigate.You mentioned testing it with a 3V AC DC adapter. Is that what you have checked? What else have you looked at. Use this guide [guide|111640] to tear it down. Then take a couple of good pictures and post those with your Question. Lets see if we can identify any issues. Your Monotron will work with 3 V but it uses a boost circuit that brings the voltage to 5V. I would start with the boost circuit and check IC1 TPS61071
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