I would like to post my experiences regarding typical problems with tape speed variations. I have fixed about 200 walkmans from Sony, Panasonic and Aiwa. However, I collect and repair only full-metal body autoreverse models made cca. after 1989. But most of my observations are valid for any model.
Many people think that these problems are related mostly to wrong belt used, but my experiences are little different. So here is my knowledge listed in the lowest to the highest probability order.
1. Some mechanical deformations in cassette compartment.
Mostly after walkman fell down to ground 🙁 It is also very probable at cheap plastic models, where plastic door is self-deforming after 20-30 years.
2. Dry capstan bearings
It will affect W&F a little, but it is not as audible as on cassette deck (as basic W&F of cassette deck is much lower). Lubrication is necessary every 20 years (even if walkman is not used). Use oil used to lubricate watches. I use oil with density “2” used to repair men’s watches.
3. Dirty or dry moving parts of walkman
Every dirty or dry moving part will result in increased resistance and therefore negatively affects W&F. If walkman is in good condition and it has no battery leakage traces, then it should not be a problem.
4. Dirty capstan, pinch rollers and head
Well, nothing to say 🙂
5. Wrong motor
Quite often this is the case. The gap between the rotor and the stator is very small, sometimes they scrub each other (some Sony models). Generally, the motor quality is very high (I think they’re made to work forever), so it is enough to disassemble and re-lube them.
6. Dirty capstan or motor wheel after belt change
Be very careful when replacing old belt with the new one. Especially if the old one is turned into goo. You have to clean the belt path very very carefully and check for any remains of the old belt. I use benzi-alcohol for this purpose.
7. Worn belt
If the belt is too loose, then the walkman will not operate correctly (you will not be able to change the functions). When the belt rubber self-destruction process starts, it will take only short time (several weeks or months) until it melts, so it’s quite unlikely that you experience problem with W&F because of worn belt. You will rather see it as “walkman not working at all”.
8. Wrong belt size
For many people, this is the most probable cause of W&F.
Belt of the correct size is necessary for the lowest W&F, but even if you use different one, on non-DD models it is hardly audible. I tried experiment with 54×0.8 mm belt instead of 68×0.6 – and it works great on Panasonic and most Sony models! If you experience wrong behavior after the belt change, check also for another reasons, like dry motor bearing. Most walkmans use belts of 0.5 to 0.6 mm thickness. These belts are not made any more and are very hard to get. I had to order production for myself. If you need any, just contact me.
If you want to use thicker belt, it is possible, but not recommended. Just be careful – some capstan wheels have the groove width of 0.7 mm, so please, use 0.6 mm or 0.8 mm, but avoid using 0.7 mm belt (the gap width cannot be the same as the belt itself).
Also, if you use thicker belt, the capstan bearings and motor will wear sooner.
9. Wrong belt quality
Check for the belt width uniformity and other defects. They’re quite often the cause of problems
10. Wrong pinch roller
Not only belt rubber destroys itself after 15-20 years, but the same chemical process starts at pinch roller as well. The rubber either hardens or softens. Both have negative effect to the W&F and usually it is very audible. Some earlier Sony models use pinch roller that is only very little wider than the tape itself, so the pinch roller is not able to hold tape on capstan. As the rubber hardens or soften, the resistance between pinch roller and capstan decreases.
If you listen to tape and W&F is audible more with some tapes and less with another, then it is very probably the pinch roller problem. Also, if it is more audible on one cassette side than on the another one, or, it is more audible at the end of the tape than at the beginning, it is very probable pinch roller issue (not necessarily true for models with two separate belts for each capstan, like later Panasonic RQ-SX series)
11. The winner is – polished capstan
Yes, if the walkman is used quite often, the capstan surface is not rough enough (it is roughened at production) and it is not able to hold tape on pinch roller. The symptoms are the same as in the previous case.
The help is quite easy. Dip the contact part to the saturated solution of FeCl3 (you can buy it at any shop with electronic components) for about 5 seconds, wash it and the surface is roughened again. Dip only the tape-to-capstan contact part. Never dip the part that is in contact with capstan bearing.
If you have any other experiences, please let us know 🙂
EDIT: I get lot of questions regarding suitable oil. Do not use sewing machine oil, as it dries quickly. Use quality watch oil, like the one listed on eBay ID: 220964943928. It costs 2 Dollars only including shipping 🙂