Anyone have a suggestion what would cause this?

Model?

But if that isn't the cause it is your motor acting up and you can adjust your motor speed by adjusting your motor's potentiometer. That's why retrodos was asking you which model(walkman ) you were referring to.

For now :

http://www.vintage-electronics.cc/cassetterepair.pdf

Is it a Sony D6C by any chance?

My Sony ZX-7 does this from time to time.

This mini boomer's tape transport is one of Sony's DD type, so maybe it's having a similar problem.

Advice I got a while ago involved replacing components & electronics knowledge that is beyond me.

Its a techsonic j1. It plays super fast -   as in hi speed dubbing fast.   i thought there might be a short in the hi speed engage button but i am also open to suggestions.  thanks in advance!

Have you opened your's up yet a checked out the Hi-speed dubbing switch, whether it's stuck or broken?

i did open it up and it was obvious someone had before me since over 2/3 of the back screws were missing.   The hi speed dubbing switch engages and does make the tape speed up slightly.    I also tested it with batteries to make sure it wasn't some weird voltage issue.   It says 120/220 volts on the back label but there isn't a switch for it  anywhere to be found.

Without having the inside backside of this model in front of me: as i dont have this model...

Have you traced from where the A/C current enter's to the box the wires to the transformer and seen how many tap's are on the the transformer 'outgoing' as this will allow you to find the switch for the 110/220 if this model has this feature regardless of what the back lable says, as some model's of some brand's of boombox's used the same chassis and parts but maybe omitted some parts true to the orginal manufacture of which your's may Not have ( as yours may be a off brand manufacture - I dont know ) 'world-voltage' as it may say on the back but not any switch provided in your particular model.

    You need to check your voltage's from the wall power depending upon your country?

Here in the USA it is about 117 Volts You should follow this voltage in your unit untill it get to the transformer, and then check the output voltage ( should be about 17 vac )  before it get's to the diode set or the fullwave bridge.  after the diode bridge it should be 12 or 15 dc volts again depending upon how many batteries this take's, then follow this voltage to the rail's in the mainboards and ensure that it is the same to most of the place's 'it' should go...