Cleaning those damn switches in cassette decks??

[Doug Tymofichuk]

On Thu, 02 Sep 1999 12:19:53 +0900 The Dark force of dance 
<batzman at all-electric.com> wrote:
> 
> I'm guessing here that it is related to another curious 
> problem the cassette deck seems to have. I wouldn't have 
> thought this too critical but when I think about it, it 
> probably has great bearing on the case. The supply real has 
> very little, if any tension on it. Which means when you 
> fast forward and stop, the supply real keeps turning until 
> it looses momentum. This forces a small amount of tape to 
> bunch up inside the cassette. This slack has to be taken up 
> before it begins to pull the supply real around again.
>
This is normal for a lot of cassette decks, and so is 
likely not the problem. Very few cassette decks have actual 
*brakes* on the take up reel, however, when in play mode, 
the take up reel is driven to supply tension to the tape. 
The amount of tension is determined by a clutch assembly 
somewhere in the mechanism, and if this clutch is weak it 
*may* cause this problem. However, you are more likely to 
have a problem with the machine *eating* tapes if the 
clutch is weak. When in play mode, most cassette decks 
should have a take-up reel drive force of between 40 - 60 
gm-cm, measured with a special test tape or gauge. If you 
put the machine into play mode without a tape and with the 
door open, (you may have to defeat some interlocks to do 
this), there should be a significant drive to the take up 
reel, but you should also be able to stop it fairly easy 
with your fingers. If this tension is either too high or 
too low, it *may* cause this problem.

In my experience, this problem is typically caused by 
problems with the capstan/pinch roller assembly. 
Mind you, if the head itself is very far out of alignment, 
that could mess things up too. The first thing to check is 
cleanliness; any dirt on the capstan can be a problem, and 
sometimes there are fragments of broken tape jammed in the 
pinch roller from a previous problem. If everything is 
clean, then check that the pinch roller turns freely, and 
then check for slop in the capstan bushing itself. If you 
push sideways on the capstan in every direction and there 
is any significant movement, then it is worn and will not 
stay in correct alignment, causing the tape to slide up or 
down. A new bushing is about the only answer to this one. 
There are also special test cassettes with mirrors built in 
so that you can watch the tape as it travels across the 
head and see where the problem is (sometimes!), but you 
probably don't have one of those.
 
> Now if my guess is correct, this deck relies on their being 
> some tension in order for it to pull the tape tight and 
> guide it through the heads. With no tension on it, the tape 
> could have a propensity to wander. Especially with large 
> tapes such as C90s. The evidence seems to suggest this with 
> shorter tapes. C10s and even C30s having little trouble.
> 
You will always experience more alignment problems with 
longer tapes, as the actual tape is thinner (to fit on 
the same size of reel) and more difficult for the system to 
handle. As well, some brands are worse than others for this.
> 
> Here's fingers crossed I don't have tiny, exploding, 
> spring-loaded bits flying around the room.

Ever opened up one of those modern automatic point-&-shoot 
cameras? Ka-sproing!!!
 
Doug
----------------------
Doug Tymofichuk
dougt at cancerboard.ab.ca