Hello guy's been a while since i was last on line, anyway i have a couple of weeks off work so decided to check the speed of my Aiwa hs-px101. To do this i have a Sony wm-d6c,dd-33 and also dd-9, but before doing this i thought i'd compare these to my Aiwa xk-7000( recently had new belts all round and speed seems correct compared to my cd players), i was surprised to find the d6c sounds faster than both the dd-33 and dd-9 but very close to the xk-7000. I tried listening to a variety of music over a period of days( sometimes when your tired your ears play tricks on you an what sounds now may not be later on), only to arrive to the same conclusion. Not sure if i should adjust the speed on my dd-9 and dd-33, i know the dd-9 has belts but the dd-33 should be spot should'nt it although it does suffer from the infamous clicking gear. Any thought's on what action i should take.

Speed in general (Non DD)

There is usually a variable resistance potentiometer type component either visible by the side of motors or built into motor casings that can be adjusted with an optician's screwdriver

a) You either try adjusting 'by ear' a familiar song or a guitar TONE (like the A tone) recorded on a stable piece of equipment

b) take a c30 (30 minutes tape) and time it ...one side should play 15 minutes

c) using an oscilloscope (ouch, yikes! Yes...I know )

Speed Issues D6C

Got this on the net :

If your WM-D6C has a serial number below 267201 (take out the battery block and you'll see the serial number sticker there) then the problem is electronic, not mechanical. It is likely due to the speed controller chip (labeled as IC601 on the circuit board), which is made by Sony and is type CX20084. This chip decides the voltage that is fed to the motor which is only about 2.4 volts, Should the chip be defective then the motor receives about twice this voltage and thus runs too fast. If you take the back off the recorder you will see the circuit board; it looks like a rectangle with a small square extra bit sticking out to the right. It is here that the IC601 resides. It is about the size of a small pinky finger nail and has 8 tiny legs down each side. Measure the voltage on pin 15 (put one voltmeter probe (+) on the second leg down on the right side (pin 15) and the other one (-) on the battery negative), it should read about 4.8 volts, which it feeds into the base of transistor (Q601) that in turn will then feed 2.4 volts to the motor (if everything is working OK). If the chip is damaged, then the voltage on pin 15 will be close to zero, and the transistor Q601 will not be "held back" and so will feed about 5 volts to the motor. CX20084 is (unfortunately) obsolete, someone in the UK sells them for about $50, but an excellent company in Hong Kong (utsource.net) sells them for $5 (plus $8 S&H). Taking out the old chip and putting in a new one is close to microsurgery, you will need a micro soldering iron (18Watt Antex), a good eye, a powerful magnifying glass and a steady hand, but it can be done - I've done it! There is a possible second reason that could cause the motor to run too fast. There is a pick up coil on the main flywheel called FG901. If this is damaged it will be open circuit and then the only use for your recorder is probably a paper weight. You can test this by going back to chip IC601 and locating pin 1 (top left pin; a small circle on the body of the chip is next to pin 1), Pin 1 is connected to the positive side of a capacitor,  C602 (0.47 microF), check the resistance from the negative side of C602 to the ground (take battery out, and use battery (-) as ground). You should get about 600 - 650 ohms reading. If you get nothing, sorry there is not much you can do about it as these pick up coils are definitely not available. Finally, chip 601 (CX20084) goes bad if you connect the batteries back to front

You can check out what Retrodos has done :

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Hi, Doc thanks for your reply but the speeds of my walkmans are only slightly to fast or to slow, they never fluctuate massively(no were near twice normal speeds). I have recently compared my Sony wm-d6c with too of my direct drive technics cassette decks, and it seems that possibly it's the dd-9 that is playing just a bit faster than the dd-33 and the wm-d6c(also have never used a main's psu with any of my walkman's). Also have 2 sony wm-7's and have noticed one side play's alittle quicker than the other is this normal or could the belt be at fault.

Belts can't increase/decrease the speed with 'consistency'...you'll notice a warble /wow & flutter when there are problems with the belt or the pinch roller causing uneven tape transport.

There are these minor inconsistencies between unit to unit because for all that you know all these tape players were finally adjusted by a technician in an assembly line? Or age could have introduced a slight difference in the parameters resulting in a slight change in motor speed. I always adjust the motor speed to suit the situation.
Players with two dedicated motors for forward and reverse may give you differing results based on which motor is active....similarly head azimuth/alignment changes may make the playback of one side seem sharper than the other unless you check out with SIDE A/same song both in forward and in reverse.

Most newer muitimeter measure frequency and you need a 3 khz test tape. If you make your own, use a trusted recorder.