Although these terms sound a bit romantic ...reminiscent of wedding 'vows' and heart 'flutters' and sentimental tears ....these words often cause an audiophile immense misery and true tears of anguish ....poetic enough ?

Now seriously,

In your good old gramaphone Records you might notice discrepancies in the sound at regular i8ntervals...usually once per revolution because of an off center or worn out hole in the center of the record.

Similarly if the transport of magnetic tape across the playback head is not smooth/regular/even you hear the equivalent of an auditory wobble. Naturally now the situation is a bit more complex related to the capstan (related to belts & motor)/the pinch roller and to a certain extent 'idler tyres'

Normal accurate methods include the use of a test tape ( recorded on standardized equipment) like Sony's WS-48A (3 kHz, 0 dB) to verify if the unit being tested can reproduce the test tone with 'high fidelity' ... an almost exact/truthful reproduction. This output can either be tested using an oscilloscope or using 'oscilloscope software' and a PC as detailed in this excellent thread:

index.php?board_oid=193392314111653483&content_oid=288255372207748108

But what do common folks like you and me do....we got by 'ear' adjusting motor speed and choosing between belts (thickness and size variations can cause less/more tension resulting in wow flutter variations) flipping over/replacing idler tyres or carefully rejuvenating their surfaces with fine emery just as the case with pinch rollers that have gone all 'shiny' with not enough 'grip'. And not to forget ...fine tuning the alignment of the playback head by clockwise/anti clockwise adjustments of the 'screw' ...azimuth adjustments

But like deviations in heart sounds...murmurs...through a stethoscope...wow and flutter indicate an imbalance in the precision of the tape being transported....and this imbalance can cause  wear and tear consequences in the long run.

PROBLEMS :

As with the moving parts of an engine ....you need repeated servicing. Once adjusted these units WON'T stay adjusted indefinitely. When the belts start becoming slack or when the pinch rollers get a little too stiff & shiny with age & lack of maintenance the problem creeps back and the need for recalibration presents itself once again

If you have only 3 or 4 walkmans /Boomboxes / tape decks you are blessed, and all the more lucky if you use them in rotation. If you are like me, happy to shelve your collection and gaze at them from time to time 'lovingly' you'll have a nasty shock when one day you reach out to use one and it either doesn't work at all (as disuse has allowed the belts to deteriorate) or does with moans and groans .... Fate doesn't just hang by the thread it depends invariably on a piece of rubber

I was just going to make a flippant remark about not liking mist on my flutter but actually having read your informative post I now know something about wow and flutter which I knew nothing about before!

Ah, yes, the fine doc! Shows he's a doctor by trade
Going in with superb set of doctor's and dentist's "tricks" - stethoscope, fine tuned ears, dentist's tools and materials in skilled hands,...
I, being a techie, am patiently waiting for my WS-48B and P-4-A100 tapes to arrive.
Then, together with doc's belts, I plan to finally revive the few "patients" I have

Test tapes :
SONY P-4-A81 Azimuth Tape

P-4-L81 Level Set (333Hz, 0dB)
P-4-L82 Freq. Res. Test (333 Hz ,-10dB)
P-4-A82 Freq. Res. Test (10kHz, -10dB)
P-4-A81 Azimuth
SPC-4  Speed Test (1kHz, 0dB)
WS-48 Wow Test (3kHz,0dB)
CS-10  Rec Test (blank tapes for testing)
CS-20  Rec Test (blank tapes for testing)
CS-4-1 Rec Test

MC-112C Mirror Test tape

WS-48B available from Sony for approx $30:

https://www.servicesplus.sel.s...lts.aspx?stype=parts

lot of test tapes available on ebay/amazon

Examining the causes of the problem :

1. The Motor : Unlike motors in your toys a good walkman motor needs to be ideally 'brushless' . A unique design variations away from the typical cylindrical shape was with the flattened wm10 with stationary flattened out motor coils forming the 'stator' and a thin disc with it's central spindle (forming the capstan) forming the rotating part or rotor.

Essentially the preference would be a motor than can run fast and smooth without needing user maintenance.

Maintenance : You will almost never encounter a 'dirty' motor. So there'll be no actual need of 'cleaning' but you could place a teeny weeny drop of sewing machine oil ( or in my case dental handpiece lubricant ) at the exit point of the spindle (which usually has the bearings and in some instances forms the capstan)

2. Voltage supplied & its regulation. : The wm 10 and its siblings use a 1.5 Volt battery and this has been the same with quite a few of Sony's subsequent models. Aim : To decrease the space used in the housing for batteries (hence Gum Stick batteries subsequently) Problem ...not enough voltage to run a high speed motor  Solution : DC DC step up convertor to provide the required higher voltage.

Older walkmans just had a potentiometer that allows you to adjust a 'set' speed. This is useful soon after a belt change. By the time you need to change a belt there may be  wear and tear aspects in the sequence of moving parts and probable difference in belt thickness/rubber stiffness/tension in case it is an OEM one (or one of mine ) that might make you feel the walkman is playing at a different speed. If you are 'high tech' you may use a speed test cassette to adjust the motor speed...if not do it by 'ear'

Walkmans like the DD9 for example are 'quartz locked servo regulated' meaning that there is a quartz crystal (crystal oscillator) that emits a standard frequency that serves as a reference . In the DD9 there's a flashy little black/silver/black wheel that spins when the unit bis in playback and a 'photo interrupter' detects the frequency of this light dark alteration during spinning as the 'rotations per minute' or rpm and cross compares it with the ideal frequency standard of the quartz crystal. Be it high or low the 'servo' of feedback circuit either increases or decreases the speed 'live' then and there

The servo circuit can go cranky as seen in the D6C and its servo control IC.

Maintenance :

Apart from the potentiometer adjustment with a tiny screwdriver the remaining stuff like the DC DC convertor or Servo ICs involve a slightly deeper understanding of electronics & steadier hand for use with a soldering iron which we'll leave to the more experienced/proficient of us

3. Moving parts/linkages linked to the motor

You either have the regular belt driven drives and the Disc Drive (DD) type drives without belts.

Having a series of interlinked gearwheels allows for precise transfer of momentum from the motor to the cassette without wow & flutter issues. On the other hand belts are known to get loose and even deteriorate into a sticky gooey mass needing cleaning & replacement

Maintenance :

DD:

The only critical maintenance we need to discuss about the DD types (except the belt driven DD9) is the possibility of a cracked gear. Both options of repair (adding a tooth into the gap vs circumferential filing of the inner hub) have been already discussed on the board with almost equal success...but as a dentist I love adding in teeth

BELT Driven : Once a belt turns to glue you'll want to carefully clean ALL the residue using solvents like isopropyl alcohol or commercial solvents like 'Sticky Stuff Remover (thanks Minty) and GooGone (Thanks Nishant)

As with any solvent make sure you are not dripping the solvent on any other rubber/plastic parts . No point ending up with a hazy cassette window or a solvent-melt in fingerprint like a dinosaur fossil

I use earbuds, yes but also started using a length of solvent soaked twine  as this cleans the pulley grooves if you run the twine along the belt path and gently pull too and fro....much like flossing

Any residue left will give you a bump bump add on wow/wobble...CLEAN CLEAN & RE CLEAN

Don't get any solvent on the fresh belt or it'll be Belt Gone thanks to Goo Gone

The DD9 for example has added fine adjustments that can be made to the two motors and the position they sit in minimizing wobble/play that may result in wow & flutter. In addition to belts the DD9 also has 'idler tyres' and these may require replacement as well

4. Tape transport : The Capstan, Pinch Roller, Tape track & Head Azimuth

The capstan spins and the pinch roller as the name suggests is so close to the spinning capstan that it rotates as well and grabs the tape by pinching it....once you supply it with a continuous length/feed it can transport the tape across. If the spools aren't turning at a proper speed but the pinch roller is doing its job you'll end up with a beautiful Japanese Fan fold length of tape UNLESS the autostop mechanism kicks in...then you'll just see a tiny loop of tape out of the cassette.

Maintenance :

Clean the capstan & pinch roller with an earbud dampened with 99% isopropyl alcohol.

DO NOT USE ACETONE/NAIL POLISH REMOVER

If the pinch roller is all shiny and stiff ( tape slips)...use extrafine emery held against the pinch roller to strip off the top layer exposing a fresh layer that can 'grip tape'. You can try commercial 'rubber rejuvenators' like Techspray (1612-2SQ) or drum/roller cleaners for printers (thanks Retrodos)

Align the head using a Mirror Cassette if you need to and fine tune the azimuth (left/right rotation of the 'head screw' till the music sounds sharp/in Autoreverse units test both sides & adjust) by ear or by the professional methods discussed.

5. Cassettes :

Last but not least all this care is in the assumption that you have a few decent enough cassettes.

Type I : a polyester film with a layer of gamma ferric(Iron) oxide as the 'recording medium'

Type II :A polyester film coated with Chromium dioxide or Cobalt absorbed Iron oxide

Type III : Ferri Chrome : a mix of one & two

Type IV : Pure metal particles (not oxides) 'Finavinx'

Audiophiles swear by metal cassettes like TDK MA-R, TDK MA-XG,Sony Super Metal Master &  Maxell Metal Vertex. Essentially what you want is  a recording medium that can record a wide freqeuncy range housed in a durable low friction housing.

Maintenance :KEY WORD 'Coatings' ...If you don't use your cassettes regularly you might have problems with 'fungus'/mildew where you'll have to painstaking clean the tape by running it against a soft cloth pad.

Sometimes the felt pressure pad ends up with that tiny felt rectangle falling off...can be stuck back with a tiny drop of rubber solution adhesive/Superglue

Worst comes worst you'll have a batch suffering from 'Sticky Shed Syndrome' The glue/binder that holds the coating onto the polyester film deteriorates.

Cut tape can be spliced, Chewed up tape will have to be ignored...I don't really think you should try 'ironing the wrinkles out' 'Some wrinkles in the elderly lend a regal air' should be the attitude of reluctant acceptance

6: Conversion

That previous post was the last...this is the 'least' ..ignore it ...just the nag nag tiny voice of modern reason that says Go Digital Bro! If you have tapes you love archive them sort of stuff

Just for the sake of completing a writeup without sounding blasphemous on my beloved site dedicated to analogue worship ...here's something interesting

Celemony Software's 'CAPSTAN' ....Wow & Flutter removing tool

DocP Thanks again for an Interesting read

This info is priceless.....I've never thought about flossing to remove the gummy residue. DocP especially around the hard to reach areas (ie the concave belt guide on a wheel)

So simple yet so effective!!! 

I have replaced a few belts where there was no belt left, just black tar.

I often wonder what would cause this, do you have any ideas?   

Just the breakdown of petroleum based rubber compounds I'm afraid. The chemical composition deteriorates and becomes goo.

DocP's advice is as good as it gets!

Are replacement pinch rollers available in Europe? I need rubber rollers for WM-36 and WM-190.

many thanks, Rich