my panasonic rx 5100 does not have any kind of hole on the motor for adjustment, and the tape is playing a bit slow...just enough that if i record a tape on it, then play it on another boombox, it sounds a bit like the chipmunks. I followed the advice of another discussion and followed the wires to the main pcb connection, but there are no pots near that point. does anyone have any experience with a similar model?

i have seen other models with the same setup with some with a fixed voltage where the motor has no adjustment.. i thing i had put in a motor that had a adjustment hole because thats was the only motor i had and it worked making sure working voltage is the same for motor..

From my experience,if the motor has no adjustment,there is ussually a speed adjustment pot near where the power for the motor is on the IC board. It should be styled like the trimmer pots near the tuner board.

I've oppenned about eigth Panasonics ...
In five of them, there isn't a speed regulator.
Niether in the motor or the main board.
That's because early motors used by Panasonic aren't electronic. The speed adjust is near impossible, since you need to open the motor, take the rotor appart and adjust a screw (or two depending on the model).
The rotor has a switch mounted. As it spins, the switch moves outter and opens the circuit.
If it spins slower the swtich closes and the motor is powered up again.
This kind of regulator keeps the motor turnning ON and OFF to achive a desired speed (an early PWM), instead of an electronic that keeps the motor always ON but at an specific voltage (internally generated and regulated trough the hole) to control speed.

This motor is from 1981, I replaced it bacause I couldn't get it adjusted. It doesn't have any electronics.

Dissasembly



Rotor, and the on/off switch. The switch is a spring, so turning the screw let a different spring force against it, and a different speed would be needed to open it.





I you have replaced the belt (is the mecha with the falt one ?) check the size.
If the speed has changed without changing other thing, perhaps you need to change the motor.

Any mabuchi/mitsumi 2400 RPM generic motor (that matches the voltage and rotation direction) WILL WORK OK. Panasonic is a friendly BOX to service. You will fix it without effort.