D6450 datarecorder

In the D6540 after disassembling and putting the 3d wheels, the tape turns when you press "PLAY" and the rewind forward or backward, as well as the stop works, but the "Monitor" button although it is in the "ON" position does not hear the sound, I have tried it with tape that loads without problems in another cassette but I have not been able to load even the header. I have tried to adjust the azimuth but as I can't hear anything I don't think it will do much good.
The wires to the speaker seem to be fine.
Any ideas?

hello, I too have a philips nms1515 \ 00 recorder that works only the play and not the REW and not even FF. Are you sure it's due to broken gears? I tried to disassemble the recorder to check the gears, but it is not easy to get inside the front, at the moment I only see the two rear gears. there is no video for disassembly and repair ?? thank you

Thanks for the reply. I was able to disassemble the inner part and view the gears in question .. FF and Rew don't work! There is a white support with 2 pins that moves when I press FF and Rew, but having no gears it does not transmit any movement .. it seems the 2 gears are missing .. how do I upload the photo ?? Thanks

thanks, but an error comes out every time I try to upload a photo ..

It is 7 Mb, it doesn't seem too heavy ..