It is a real pain when you have to look for a replacement drive belt for a stereo cassette player. The amazing thing is that you can find a belt for almost any Walkman from online shops, but the main problem is price. Many belts are obsolete, and in limited supply, and stockists tend to hike their prices to unrealistic amounts.
Unfortunately, for the stockists they cannot hold onto those belts forever. Rubber has a finite shelf life and eventually will degrade just by sitting on the shelf. Have you opened up an old tape recorder only to find that the belt had melted? That is what happens to rubber over time.
Electronics shops do not always mention all the details of a belt. One typically finds sketchy details. For example, many stockists will not mention the thickness of the belt. Sometimes you buy a small bag of assorted belts, none of which will be the correct thickness.
Sometimes there is no indication of the diameter or the circumference of the belt. Sometimes they mention the term 'girth' to mean circumference. Even worse, sometimes the values are in inches mixed with other values in millimetres. Therefore, if you are looking for a belt of a particular size, the first step is to collect its measurements in millimetres and inches. My calculator below can help with that. It will calculate the diameter given the circumference, and provide the values in millimetres and inches.
I needed a drive belt for my Sony WM-EX610 Walkman. This is a typical Walkman model with an auto reverse function. The internal mechanism utilises a dual capstan design that is common to most Sony WM-EX series models.
Walkmans are very forgiving when it comes to belt sizes. One can use a wide range of belt thicknesses providing it fits the pulleys and there is enough clearance. Sometimes a thicker belt is a desirable upgrade, as it will last a little bit longer.
If you look at the photograph above you will see the dual capstans. If the Walkman you have has the same arrangement, then chances the drive belt will be similar size. On occasion, I have even taken belts from Panasonic models with the same arrangement to Sony models and it worked fine.
Hunt for the elusive 0.8 mm thick belt
I measured the broken drive belt and found it to be 200 mm in length. This length is of course the circumference. If you divide this value by PI, which is 3.1415, you will get the diameter of the belt which is 64 mm. Using a micrometer tool, I measured the thickness of the belt to be 0.787 mm × 0. 787 mm, square cross section.
I had many belts that were 1.2 mm in thickness and I tried those, but unfortunately, it did not work. It seems to fit fine on the pulleys, but the problem comes with the clearance between the two pulleys, as shown in the photograph above.
On the Internet, encompassparts.com was the first stop and sure enough, they had the part number 3-220-035-01, unfortunately, they wanted £21.00, which was not economical. Therefore, the next step was to search for a cheaper alternative.
Whilst many online shops will have drive belts, they will be 1.2 mm in thickness. Specialist shops that stock 0.8 mm thick belts will tend to ask a lot for it because they know that those belts are in limited supply.
The alibaba.com site sells many drive belts in bulk but you have to search for “transmission belts” to get a listing for audio drive belts. Unfortunately, the sellers will not know their thickness either. They tend to show a photograph of a bag of assorted belts. Often there is no information about their diameters either.
eBay and Amazon also have drive belts however the majority of them are 1.2 mm in thickness and it is one of the first paces worth looking. If your cassette player can work with a thicker belt, then you are lucky.
The mcmelectronics.com site had a wide range of belts and MCM Part #: 42-235 seemed like a good choice that could work. Although slightly shorter than what I needed, it had a chance of working. After much head scratching, I managed to work out that this belt was 7.432 inch (188.77 mm) in circumference, which is 60.09 mm diameter. The belt thickness was 0.031 inch (0.7874 mm). The best part was that it cost $1.40, but the down side was they do not ship to UK. Hey, what is wrong with us Brits? Remind me to launch a letter of protest to President Obama. :-)
I just recently contacted an Australian electronics supplier who had a belt that had a chance of working. It was only $3.09; however, they wanted $28 for bank processing fees, and $18.20 postage fees! That is a crocodile done deal if you ask me! It just baffles me how firms can operate with such high costs. I decided to go walkabouts and never return there again… :-)
I have had many emails from people saying that they make their own belts. Apparently, you can buy a reel of 0.8 mm thick elastic thread on eBay for as little as 99 pence. Just cut it to size and superglue the ends and you have a belt! I have not tried it but might just have to one day.
The SCY7.8 belt has an inside circumference (ic) of 7.8 inch, and a square cross section (c/s) of 0.031 inch, which is exactly what I needed.
The PRB belt system, by Projector-Recorder Belt Corporation, uses cross section (c/s), which is the belt width, wall thickness, and inside circumference (ic), as its main parameters for all belts. With this system, it is possible to find a replacement for almost any belt size. For square cut belts one has to look for the prefix SC. The PRB belt system has a belt for almost any audio application.
I found many suppliers of this belt on Google, however they were all based in America. Therefore, if you are a Brit, then postage will be quite high.
1 mm Drive Belt Upgrade
After seeing the postage costs, I decided to go back to my drive belt collection to see if I had anything that might fit.
The 1.2 mm thick belt does not work at all so that was out of the question. However, I had a couple of 1 mm thick belts that were worth trying. The belts I had were slightly shorter but still within acceptable range. There was a 60 mm diameter one, and a 57 mm diameter one. Both are within range and work fine.
I managed to squeeze the belt between the pulley wheel and plastic pillar guide by slight stretching it. However, once in place, it all fitted fine as you can see!
With a 1 mm thick belt there is just enough clearance between the belt and the stepper motor surface.
As you can see the capstan pulleys are able to hold the thicker belt without any problems, and there is plenty of clearance.
The 1 mm thick belt appears to be an excellent upgrade! It works really well and they are as common as muck. I tested all the functions of the Walkman and it works fine. Once thing noticeable was how powerful the fast-forward and rewind functions became, which was excellent. I suppose the thicker belt is able to transfer more torque.
I contacted a Chinese seller on Alibaba and bought a bag of 50 belts that were 1 mm thick and 60 mm diameter. It cost a fiver including postage! This will keep me tied over for a few years. There is no point buying too many belts and hording them because soft rubber tends to deteriorate over time.
Measuring Diameter and Circumference
If you have a broken belt, just measure its total length, which will be the value C. This is the circumference.
If your belt is intact, then fold it neatly and measure its length L, then multiply that value by two to give the circumference, as shown by the formula below.
C = 2 × L
It is better to calculate the diameter of the belt once you have the circumference C. You will get a more accurate value than by measuring it. Simply divide the circumference value by PI, which is 3.1415, to give the diameter, as shown by the formula below.
Diameter = C / 3.1415
How to use: You have to input only the circumference value in millimetres, and the calculator will find all the other values for you. It provides the values in inches and millimetres for both circumference and diameter.
Standard Thickness of Belts
|Millimetre||Inch||Inch as fraction|
If the thickness is in inches, this conversion chart for the popular thicknesses might help for the conversion.
List of Generic Drive Belt Suppliers
- Farnell CPC Newark Electronics
- Part Number:3-325-387-01
If you know of anyone selling drive belts at a reasonable cost including postage then feel free to email me. I will be happy to add their name to the list. If you have a catalogue then I will be happy to include that as well.