Chapter 10: Tape recorders and tapes


Many home microcomputers use casette tapes as a primary medium of storing programs. You may find them in different conditions. Sometimes you may need to record own tapes. This chapter will be about them. The procedures of recovering data from tapes and recording the data back to it on a modern PC varies from microcomputer to microcomputer, so here will be the general information about these media.

Tape recorders are mechanical instruments which should be restored like all other mechanical devices. Clean mechanical part with brush and check transmission belts because they usually are the failing parts. Remember to carefully check gears. Plastic ones may have parts broken off. In some tape recorders like Polish MK 433 or MK 450 polymer used in gears may oxidize. Such oxidized polymer is fragile and gear looses ith teeth. This problem sometimes happens in some Atari tape recorders too. Unfortunately there is no easy method of fixing it, gears can only be replaced. 3D printing of such small components is possible, but their hardness is not satissfying in most cases.
Check bearings. By rotating the motor check do all functions work properly and smoothly. If some bearing works hard, consider cleaning it or adding some lubrication, not too much. Do not apply lubrication on plastic parts, it usually won't provide better spinning.
Parts which have contact with tape are prone to two kinds of pollution. First one is pollution by tape remains or dirt, and this can be removed using alcohol or sometimes even pure window cleaning liquid on a soft piece of cloth. Just clean front parts of heads, metal bars between them and all bolts. Clean the shaft to which the rubber roller comes while playing. Clean the roller too. It is usually very dirty, so do it many times to make is as dark as possible. Avoid using sandpaper as it will make the roller surface not flat, this will make the tape not wind uniformly and may even make the recorder destroy tapes.


In old tape recorders transmission belts can fail. Here you can see new and old, stretched belts.

The second pollution is magnetic residue on heads and metal parts which have direct contact with tape. To demagnetize it you can use special demagnetization coil or transformer-based soledring iron (only transformer based, heater-based don't work). Turn the iron on about 2 meters far from the recorder, come near, and by circular moves move the heater few centimeters from heads (press play on a recorder to slide heads into tape deck) slightly blowing to reduce temperature. After minute or two with the soldering iron still on (DO NOT TURN IT OFF!) by the same circular moves go about 2 meters away and then turn it off. This "ritual" is needed because by turning the electromagnet on and off near heads you may leave heads magnetized some way. When you turn it off few meters away, you won't leave any magnetic trace.
If the erasing head (the first one which meets tape while playing, usually pushed only when "record" key is pressed) has no wires connected to it, do not demagnetize it because in some cheaper recorders erasing head is a permanent magnet and magnetization of this particular component is needed.

For no way this procedure should be used in high-grade Hi-fi recorders. Some heads in them should never be demagnetized this way.

Now you can check the recorder with tape. Test playing and recording. First, leave it on "play" for about 2-3 seconds, stop and remove tape checking is it wound properly and doesn't go into recorder. The same thing with rewind, forward, recording. 

Now about tapes. There are different types of cassettes:
 - Ferro (Iron Oxide), Type I cassettes have brown tape color. They may wear off quickly. They react terribly on environmental conditions. If you have a ferro tape which has been flooded or kept in humid environment, recover its contents and then clean head/roller of your player because in humidity oxide layer may peel off on head. They are also prone to friction wear - the layer may wear out by friction of head.
 - Chromium Oxide (Type II) tapes are draker, black tapes. They don't react so badly on environment. They are less prone to stretching or friction, and can be recorded on most typical recorders.
 - Type III is FeCr tapes, they are quite rare and are not widely used.
 - Metal (Type IV) tapes are in all colours of rainbow. I've even seen greenish ones. They need a special tape recorder providing more power in recording - then metal particles can be magnetized, and they are magnetized stronger than ferric or chromium tapes. They are usually not used in our applications.
To distinguish cassette types look at write protection brackets. If there are no additional holes - it's Iron tape. If there are small holes right near write protection brackets, pointing to the inside of cassette, this is a Chromium one. Metal cassettes have additional two holes near the center of the cassette.
In our microcomputer world, we usually never meet metal tapes. Most recordings are made on Chromium or Ferro tapes.


On the top, Iron oxide tape. Lower - Chromium tape, Two lowest tapes are metal-based.    Source: Wikipedia

There are also 3 phenomena which may prevent you from getting out the data from the tape:
1. Tape is magnetized, this is the idea of recording. It is always wound somewhere. In storage one layer may slightly magnetize the other one which is on it or below it. This makes the sound quality worse. To minimize this problem always record a tape on your soud card using the highest possible level below overload.
2. Tape is made of elastic polymer. By stretching it all time during playback or rewinding, it becomes a bit longer. This makes the recording longer. 3 or 4 seconds per 60 minute tape is not significant for your ear, but matters for the computer. And you can't do much for it because making the digital recording speed up in a computer usually makes few bits of data to be stripped off. The only thing you can do is with the detection algorithm in software which analyses the sound. For example, in Tape64 software which analyses recordings from Commodore 64 it is possible to virtually speed the recording up and down by relatively modifying time coefficients for expecting different signal changes.
3. And the thing you probably won't do anything with: Partial demagnetizations. Just for 1/10 of second or even shorter the recording level goes down, then agin up. Tape in this place lost its magnetic properties. Data recorded here is unfortunately gone. If there is some recording in a significant level, it may be possible to amplify these places by hand (using time-dependent amplify function of your wave editor and then specifying the curve), but if the minimal level is smaller than ca. one third of the normal one data is usually lost.
Sometimes similar behaviour is caused by physical deformation of tape. Rewind it, then try to record it again. In my restoration sometimes I had to play the tape 3 or 4 times to get everything off it.

Now a very general information about playing the data to a microcomputer: If you have a software which allows to export microcomputer programs to WAV files, you can record them on tape to play in microcomputer, use a tape adapter like these made for old car players connected to sound card (photo on the left) or, in some cases, connect sound card's output to microcomputer's tape input. One of common mistakes in this approach is not taking into account that the sound card may invert the signal level. The proper option is usually in a program or can be applied in wave editor. Remember to set the volume to a proper level, because most microcomputers are picky about it. Any electrical incompatibilities in sound card's output and computer's input result in more problems with volume which has to be set exactly to the working level. The same thing is for recording programs from the microcomputer to a PC's sound card.


 

Chapter 9: Monitors and displays
Table of contents

Chapter 11: Floppy disk drives


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