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cassette deck repair tips

I enjoy repairing electronics. As there's a dearth of information online about compact cassette deck repairs, I thought it handy to put some tips out there for the passing home repair enthusiast.

new belts

This is one you'll find said anywhere, of course. Tape decks (as well as personal players, recorders, et cetera) are driven by neoprene rubber belts, and they degrade. It's a fact of their existence - they last a few decades and then soften, slacken and finally turn to goop. You can replace them by searching for the right belts online - eBay is a good place. When seeking belts, you must take three things into account: the length (given as the total circumference, that is to say their length if they were cut in one place and then laid along a ruler), the thickness, and the cross section shape (square or round, usually). It is important to get this right; if you're in luck, you'll find someone selling a belt set for your device - often, however, you'll have to hunt for the right stuff. It can get expensive, I'm sorry to say.

If you're looking for belts for smaller devices like personal stereos or memo recorders you could do worse than to buy an assorted handful of belts, also found on eBay and the like. These sets will contain various sizes, shapes and thicknesses, and there'll usually be one or two in there that fit your device. These sets are very cheap and handy to have lying around.

Putting the belts in can be fiddly, sometimes to the point of having to dissemble half the machine. There's no way around it, though. Try to find service manuals or tutorials on how to do it for your device. HiFi Engine is a good place to start looking (you can see if they have yours, but you'll need to register a free account if you want to download any manuals).

imbalanced audio

This can be difficult to repair, or quite easy. Imbalanced audio can mean two things: your tapes aren't being read correctly, or your machine isn't processing the signals correctly. Barring any difficult-to-replace parts being broken, which is quite rare, both issues are reparable.

play/record switch issues

If your audio returns sporadically back to normal when you fiddle with the play and record switches on the front of your machine, there's a good chance the play-record switches aren't making proper contact. On the main board inside your cassette deck, you'll find two long, spring-loaded switches, one for each channel.

I'm aware that the picture isn't great, but I cannot be bothered to open up the deck for a picture as it's rather a hassle. I'll get to it, I promise.

Get out your contact spray (the kind that leaves no residue) and, whilst depressing the play and record buttons now and then, get that good stuff all up in there. If you're in luck, this will restore contact and your deck will play properly again.

If not, here's a simple test to see whether the issue is somewhere in the circuitry or a matter of the tape head: find the wires that come straight from the head and desolder them from the board where they attach. Switch them (the left wire soldered onto the right terminal, the right wire onto the left.) If the sound issue remains the same, there's a problem with the circuitry. If the imbalance is now switched left-to-right, it's the tape head. Don't forget to switch the wires back!

tape head misalignment

The tape head is the part that the magnetic tape touches when it is played, and if it is misaligned so that it reads the tape asymmetrically, you'll get imbalanced audio. It'll also usually cause a shift in the dynamic range - that is to say, you'll hear the audio shift more to the bassy or (more rarely) the trebly side.

You may or may not be able to fix this. In older and more high quality devices, which were built to be serviced, you'll usually be able to take off the cassette bay door to access a screw that adjusts the positioning of the head:

The tape head is pointing up in this picture. The red arrow indicates the screw that is turned to adjust the head alignment. The yellow arrow indicates the record head, which can also be adjusted if necessary with the two screws on either side.

The process is simple; sit in front of the device with your headphones on, play a (properly balanced) tape and adjust the head until the audio is just right. Top tip: afterward, take a picture of the screw. The balance has shifted before, and it may again slowly slide, so this way you'll be able to see if it's caused by the screw turning. I've not had any such trouble, however.

If there is no way to adjust the head position, there isn't much you can do aside from actually modifying the device (by bending things, for instance) or the positioning of the cassette in the bay. You can screw around with spacers and bits of cardboard, but really, perhaps your machine is just a write-off at that point.

the pinch roller

The pinch roller is a rubber cylinder that grabs the tape and rolls it along the head. Its speed is fixed, so its diameter is important; too large and the tape will play too fast, too small and it will play too slow.

Fixing a cracked, gooey, sticky or otherwise broken pinch roller is no mean feat. First things first: if your pinch roller is still in working order, measure it. Find out exactly how thick and long it is so that if it should ever crap out, you'll know what to look for or work towards.

A sticky pinch roller is often an omen of what is to come, but the stickiness can usually be wiped off with a bit of cloth or some printer paper. This will technically make the roller a bit skinnier, slowing down your tape, but when we're talking fractions of millimetres, I think you'll be okay.

A gooey or cracked pinch roller needs to be replaced. You could conceivably build one out of electrical tape or restore the surface by sanding it down and adding a layer of liquid latex (very difficult to get flat and even, which is important).

But your best chance of good operation is getting a new pinch roller. Pinch rollers, alas, do not come in standard sizes, so you'll have to look for one that is made specially for your device... it's hard, I'm sorry. If you know exactly the size you need, you'll be able to do better, but still, you'll cry yourself to sleep.

demagnetising/degaussing

There's a lot of to-do about this. Getting a demagnetiser and demagnetising your tape heads is supposed to improve sound quality, as magnetisation is said to screw up the sensitivity of the head. Now, even the experts are divided on this. As I have no experience with it, I'll report back when I've found a demagnetiser to test on my deck.
If I should run into other problems (and solutions) I will document them here, but for now, that is all, friends.