I built myself and audio amplifier circuit to play music from an old phone through to a speaker.This worked fine for a while, then the phone stopped playing to the amplifier. The sound was still coming from the phone speaker even when a stereo audio lead was plugged into the phone's socket. I tried 2 other leads but still the same result.
I then tried the same with another old phone , and the same thing happened. The phone will play music but not out through the audio leads.
I don't have a headphone set to plug in to the 2 different phones, as I only used bluetooth headphones.
I haven't tried pluging into a stereo system as I don't have one now but I could plug in my Alexa device??
The amplifier is a home built one , nothing serious at the moment , more just a try it and see, and is powered by a 9v DC power source from a benchtop power supply.
I haven't done much else, as neither phone goes mute? when a stereo audio lead is plugged in, but they did at first. That is what normally happens , doesn't it.