tape speed slows down when increasing volume

Hello everyone i have a question about an Aiwa TPR-950. I just installed a new belt of correct size and width. The problem is whenever i raise volume when playing a tape, the speed dies down. I have an Aiwa 9 volt motor in the boombox that looks original and the speed dial is all the way up to the fastest level. Any idea what the cause is? Ive read some forums about the 950 and im sure i have the right belt. Wondering if the motor is going bad or a bad capacitor somewhere?

It is more likely the rubber idler tire and not the belt at all. You do not need to remove the back circuit board from the chassis like you did to replace the drive belt. However, you will need to take the entire chassis out of the case to get to the front of the mechanism where you can see the drive tire. You will need some rubber re conditioner (not alcohol) and some pointed cotton applicators (Swisspers) The best thing to do would be to replace the tire altogether.

good luck

Thanks for the answer, have you had this problem before with a 950 or another box?

This boombox is only a 9V system and the motor probably is a 9V motor so there isn't a big cushion for motor drive current. If you look at the schematic, the motor power circuit goes through many switches. If any of them have oxidation on the contacts, it's going to add resistance to the circuits. When you turn up the volume, the amplifiers will consume more power and a drop in voltage could cause the motor circuit to be affected. Of course, leaking filter capacitor could cause this too, as well as a weak power supply or dirty switches or contacts in the power supply circuit.

I agree with super, sounds like a power problem.
If you can read the voltage supplying the motor as you turn the volume up/down, that should confirm or deny it.