Cassette tape riding up capstan
u1061771156
part was inoperative, soon traced to a broken belt. However replacing
the belt has shown up another fault: the tape rides up the capstan
and eventually goes over the top and ends up behind it. Cleaning the
tape path didn't help.
The pinch rollers were, predictably, hard and glazed and miserable.
The obvious cause! However having replaced them with nice new ones
it's made no (or at least very little) improvement. On some test tapes
it only lasts a second or two before the tape flips up.
It's an auto-reverse dual capstan unit, and both directions are
prone to this riding up, one direction however being much worse than
the other. Pressing the Fast-Forward button (which lifts the pinch
roller away from the capstan) slightly - reducing the force on the
roller - will also make it flip immediately, on either capstan.
There's a slight (barely noticeable) wobble on the capstan bearings
but could that really be enough to cause such a serious problem? By
eye there's no obvious misalignment of anything. Slight wear on the
head. No sign of anything having been forced during its life. In
general it looks a well engineered unit, of the type where the
capstans and motor and spindle drive are on a "tray" that slides up
under the tape, as the tape is pushed in horizontally open-side first
into its slot.
I'm mystified at present, and looking for suggestions.
Best Regards,
Mike.
WEBPA
Riding is often caused by the pinch roller's axis being slanted with respect to
the capstan's axis. Not just in and out, but laterally. Worn capstan bearings
will do this. If you can't replace the bearings, try a full disassembly, then
carefully "stake" with a center-punch around the shaft hole. Works sometimes,
fails more often, but it's all you've got.
Paul Weber
Albuquerque, NM
we...@aol.com
webpa
Jerry G.
to a bad pinch roller, or dirty capston shaft.
If the above are in proper order, then there are the mechanical
problems to look for. The capston bearings or shaft itself can have
some wear. Or, the capston bearings can be warn out casing it to be
a bit tilted.
Also check for any uneven pressure of the pinch roller against the
capston shaft. If the roller pressure is stronger at the bottom for
example, the tape will ride up.
I had a similar problem in a tape machine. It ended up being that the
machine was dropped by the customer. The chasis was bent just a
little bit out of tollerance...
--
Jerry Greenberg
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u1061771156 <u1061...@csi.com> wrote in message
news:slrn81mkgt.7...@csi.com...
User1
out to be the felt on tensioner came unglued.
Steve Herns
Usually this effect is caused by not enough torque being given by
the Take-up reel. Examine both Take-up reels, look for a common piece
of the Mechanism related to both reels.
Could be a Idler assy thats worn out and not gripping the reels,
or a piece of debris caught somewhere causing the reels to drag.
As long as the Pinch roller assy has little or no up/down play
if you pull on it, and the Capstan isnt basicly falling through
its hole...then aim 4 the reels.
U >I'm working on a car radio cassette (Blaupunkt NY SQR05). The cassette
U >part was inoperative, soon traced to a broken belt. However replacing
U >the belt has shown up another fault: the tape rides up the capstan
U >and eventually goes over the top and ends up behind it. Cleaning the
U >tape path didn't help.
U >The pinch rollers were, predictably, hard and glazed and miserable.
U >The obvious cause! However having replaced them with nice new ones
U >it's made no (or at least very little) improvement. On some test tapes
U >it only lasts a second or two before the tape flips up.
U >It's an auto-reverse dual capstan unit, and both directions are
U >prone to this riding up, one direction however being much worse than
U >the other. Pressing the Fast-Forward button (which lifts the pinch
U >roller away from the capstan) slightly - reducing the force on the
U >roller - will also make it flip immediately, on either capstan.
U >There's a slight (barely noticeable) wobble on the capstan bearings
U >but could that really be enough to cause such a serious problem? By
U >eye there's no obvious misalignment of anything. Slight wear on the
U >head. No sign of anything having been forced during its life. In
U >general it looks a well engineered unit, of the type where the
U >capstans and motor and spindle drive are on a "tray" that slides up
U >under the tape, as the tape is pushed in horizontally open-side first
U >into its slot.
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u1061771156
>Hi Mike,
> Usually this effect is caused by not enough torque being given by
> the Take-up reel. Examine both Take-up reels, look for a common piece
> of the Mechanism related to both reels.
>
> Could be a Idler assy thats worn out and not gripping the reels,
> or a piece of debris caught somewhere causing the reels to drag.
>
> As long as the Pinch roller assy has little or no up/down play
> if you pull on it, and the Capstan isnt basicly falling through
> its hole...then aim 4 the reels.
Thanks for the suggestions, Steve and the other posters.
I think something in the FAQ said that too _much_ reel torque
could cause this problem. The torque when I run it with no tape
in, feels reasonable, though I don't know what the spec is
(or have much way to measure it). My past experience of reel
to reel decks has been that a capstan is quite happy to feed tape
smoothly onto the floor (or into the works) with next to no take-up
tension if a reel gets stuck. ;-)
It's hard to fiddle with the reels whilst it's going, as it has a
photo sensor on the idler and switches direction if that stops for
even a fraction of a second.
Incidentally, I don't understand how the take-up reel torque is
generated on this deck. Traditionally I've found a felt washer between
two disks, or something like that, to drive the take-up reel. This
deck has a gear type idler between the reels, with a little belt
leading from the idler to the top of a disk, and a lower disk is
driven by the main drive belt. But when I took the disk thingy apart,
no felt washer or adjustment in there. It looks like this (in cross
section): _
___: :___
> : : < <-- output belt to idler here
_ | : : | _
| H MMMM: :MMMM H |
| H |___: :___| H |
>|_____: :_____|< <-- input belt from motor here
|_______: :_______|
____________:_:_____________ (shaft it fixed to chassis)
The part marked MMMMM is a magnet (not sure how many poles or where).
The part marked HH is thin hoop of metal, looks brownish like mildly
oxidised steel or oxidised copper perhaps. The thing is capable of
transmitting static torque, so is clearly not operating on an eddy
current principle, and it is entirely smooth in operation, not
"notchy" like a motor with poles. Does this operate by saturating
the magnetic material at H and hence inducing attracting poles that
dislike moving around the ring, or something like that? It's devious,
however it works, and as there seems nothing in it either to go wrong
or be adjusted I consider it a big improvement over a felt disk
system. Seems like everyone ought to use this, unless it's
expensive or patented I guess. Nothing for me to adjust to experiment
with, sadly. ;-)
I can't feel play in the pinch roller mechanism at all, and the rollers
are an exact fit vertically in their holders (actually they were 0.2
mm too high initially, I shaved a fraction off the plastic hub so they
fitted nicely.) Freely running as far as I can tell. I swapped them
over but the worse capstan side remained worse.
I'm tempted to make up a cassette with a short loop in it, and see
how well it works with zero take-up torque, as an experiment.
I'd be particularly interested in knowing how much tilt on the capstan
is necessary to cause the tape to move. By eye it looks fine. I tried
turning the capstan bearing (it's a phosphor bronze? bearing sort of
rivetted in, and turned around with a pair of pliers without too much
effort) by 180 degrees in the hope that the worn side would no longer
be under pressure, but this didn't seem to change it. Also, which
direction of tilt would make the tape ride upwards? If I knew which
way to shift the bearing, I might be more willing to try (but I
don't like that idea much, really.)
Still puzzled,
Mike.
JackH35785
assume you realize the head contact pressure is cause by the fact one capstan
flywheel is slightly smaller than the other. Now, it is very important when
replacing these two neoprene belts is that they are not twisted. They must be
oriented to be running perfectly flat. You are correct when you discovered that
the holdback tension is cuased by the felt washers. These can actally be
carefully washed with soap, rinsed, patted to dry.
Jack
Steve Herns
U >Thanks for the suggestions, Steve and the other posters.
U >I think something in the FAQ said that too _much_ reel torque
U >could cause this problem. The torque when I run it with no tape
U >in, feels reasonable, though I don't know what the spec is
U >(or have much way to measure it). My past experience of reel
U >to reel decks has been that a capstan is quite happy to feed tape
U >smoothly onto the floor (or into the works) with next to no take-up
U >tension if a reel gets stuck. ;-)
Yep, same with Cassette players too.
My diagnosis here is basicly that there is *SOME* torque, but just
shy of enough to keep up with the Capstan speed.
That condition will cause a 'Walking' effect, gradually making the tape
ride up or down...depending on how the design of the capstan is.
U >It's hard to fiddle with the reels whilst it's going, as it has a
U >photo sensor on the idler and switches direction if that stops for
U >even a fraction of a second.
I've worked on this model b4. =)
U >Incidentally, I don't understand how the take-up reel torque is
U >generated on this deck. Traditionally I've found a felt washer between
U >two disks, or something like that, to drive the take-up reel. This
U >deck has a gear type idler between the reels, with a little belt
U >leading from the idler to the top of a disk, and a lower disk is
U >driven by the main drive belt. But when I took the disk thingy apart,
U >no felt washer or adjustment in there. It looks like this (in cross
U >section): _
U > ___: :___
U > > : : < <-- output belt to idler here
U > _ | : : | _
U > | H MMMM: :MMMM H |
U > | H |___: :___| H |
U >. >|_____: :_____|< <-- input belt from motor here
U > |_______: :_______|
U > ____________:_:_____________ (shaft it fixed to chassis)
U >The part marked MMMMM is a magnet (not sure how many poles or where).
U >The part marked HH is thin hoop of metal, looks brownish like mildly
U >oxidised steel or oxidised copper perhaps. The thing is capable of
U >transmitting static torque, so is clearly not operating on an eddy
U >current principle, and it is entirely smooth in operation, not
U >"notchy" like a motor with poles. Does this operate by saturating
U >the magnetic material at H and hence inducing attracting poles that
U >dislike moving around the ring, or something like that? It's devious,
U >however it works, and as there seems nothing in it either to go wrong
U >or be adjusted I consider it a big improvement over a felt disk
U >system. Seems like everyone ought to use this, unless it's
U >expensive or patented I guess. Nothing for me to adjust to experiment
U >with, sadly. ;-)
That magnet is usually there to cut the field of a Hall effect device
or other type of inducer. While it spins, it turns on/off the inducer
which sends a signal, usually to an IC ...letting it know if the IDLER
assy has stopped moving. ( usually for FF or REW Auto Stop)
This is a better/more reliable design than the felt clutch you describe
which is also more popular.
U >I can't feel play in the pinch roller mechanism at all, and the rollers
U >are an exact fit vertically in their holders (actually they were 0.2
U >mm too high initially, I shaved a fraction off the plastic hub so they
U >fitted nicely.) Freely running as far as I can tell. I swapped them
U >over but the worse capstan side remained worse.
I dont suspect the problem to lie in the Capstans at all.
U >I'm tempted to make up a cassette with a short loop in it, and see
U >how well it works with zero take-up torque, as an experiment.
May be informative. (where's the TRICORDER when you need it?)
U >I'd be particularly interested in knowing how much tilt on the capstan
U >is necessary to cause the tape to move. By eye it looks fine. I tried
U >turning the capstan bearing (it's a phosphor bronze? bearing sort of
U >rivetted in, and turned around with a pair of pliers without too much
U >effort) by 180 degrees in the hope that the worn side would no longer
U >be under pressure, but this didn't seem to change it. Also, which
U >direction of tilt would make the tape ride upwards? If I knew which
U >way to shift the bearing, I might be more willing to try (but I
U >don't like that idea much, really.)
I lean away from the Capstan myself....I'm assuming you cleaned the
Pinch rollers and removed any oxide brown film on the capstan shaft
(created by tapes) by using alcohol/laquer thinner or scotchbrite.
Since you say the problem is only on one side, that really points to the
take up reel for that side & or the Idler assy you described in the PIC.
With no power applied and no tape, feel the torque of both reels by
hand and see if one feels significantly tighter.
If not...it may be too slight to feel by hand, so, take off the snap
rings and disassemble one reel at a time and inspect & clean the parts,
lube the reel shaft(s) with light oil & check the end play when re
assembled. Look for exessive play up/down.
If this still gives you the same problem, move to the IDLER assy.
Check the Gear and see if its kinda hard to spin. Lube it if you're
not sure.
Usually the Idler will not be the trouble in a case like this, cause
if it works on one side good, it will work on the other.
IMO, look carefully when inspecting the reels...you may find some kind
of binding there.
Good Luck,
Steve
u1061771156
Thanks for the feedback.
Whilst this has dual capstans, it uses one when playing one side and
the other when playing the other side. I think you're referring to a
mechanism where both capstans and pinch rollers contact the tape at
the same time to regulate tape tension independent of the reels,
that's not the way mine works. As I tried to explain in my previous
post, there are NO felt washers anywhere in the mechanism. (OK, there
are two to retain oil on the outside of the capstan bearings, but I
don't count them.) Hence sadly nothing there to wash and rinse. ;-)
The belts (square, running on their corners) are definitely not
twisted. The replacement main belt isn't quite identical to the
original but I really can't see that being important, though I did
get a comment that maybe it could be (by email). I'm using a generic
belt from Maplins, just a shade wider. I can believe that the belt
could be important on a deck as you describe, where the drive power
to both capstans must be balanced to tension the tape properly.
Where could one get original Blaupunkt belts in the UK (and that sells
to non-trade people like me?)
Regards,
Mike.
u1061771156
>Hi Mike,
>
>U >Thanks for the suggestions, Steve and the other posters.
>
>U >I think something in the FAQ said that too _much_ reel torque
>U >could cause this problem. The torque when I run it with no tape
>U >in, feels reasonable, though I don't know what the spec is
>U >(or have much way to measure it). My past experience of reel
>U >to reel decks has been that a capstan is quite happy to feed tape
>U >smoothly onto the floor (or into the works) with next to no take-up
>U >tension if a reel gets stuck. ;-)
>
> Yep, same with Cassette players too.
> My diagnosis here is basicly that there is *SOME* torque, but just
> shy of enough to keep up with the Capstan speed.
> That condition will cause a 'Walking' effect, gradually making the tape
> ride up or down...depending on how the design of the capstan is.
My gut feel is still that the torque is too high rather than too
low, if that were the problem at all. The tape certainly doesn't look
as if it is becoming slack at all, more that it's too tight at its top
edge going past the capstan. See experiment below.
>U >Incidentally, I don't understand how the take-up reel torque is
>U >generated on this deck. Traditionally I've found a felt washer between
>U >two disks, or something like that, to drive the take-up reel. This
>U >deck has a gear type idler between the reels, with a little belt
>U >leading from the idler to the top of a disk, and a lower disk is
>U >driven by the main drive belt. But when I took the disk thingy apart,
>U >no felt washer or adjustment in there. It looks like this (in cross
>U >section): _
>U > ___: :___
>U > > : : < <-- output belt to idler here
>U > _ | : : | _
>U > | H MMMM: :MMMM H |
>U > | H |___: :___| H |
>U > >|_____: :_____|< <-- input belt from motor here
>U > |_______: :_______|
>U > ____________:_:_____________ (shaft it fixed to chassis)
>
>U >The part marked MMMMM is a magnet (not sure how many poles or where).
>U >The part marked HH is thin hoop of metal, looks brownish like mildly
>U >oxidised steel or oxidised copper perhaps. The thing is capable of
>U >transmitting static torque, so is clearly not operating on an eddy
>U >current principle, and it is entirely smooth in operation, not
>U >"notchy" like a motor with poles. Does this operate by saturating
>U >the magnetic material at H and hence inducing attracting poles that
>U >dislike moving around the ring, or something like that? It's devious,
>U >however it works, and as there seems nothing in it either to go wrong
>U >or be adjusted I consider it a big improvement over a felt disk
>U >system. Seems like everyone ought to use this, unless it's
>U >expensive or patented I guess. Nothing for me to adjust to experiment
>U >with, sadly. ;-)
>
> That magnet is usually there to cut the field of a Hall effect device
> or other type of inducer. While it spins, it turns on/off the inducer
> which sends a signal, usually to an IC ...letting it know if the IDLER
> assy has stopped moving. ( usually for FF or REW Auto Stop)
>
> This is a better/more reliable design than the felt clutch you describe
> which is also more popular.
The thing that sets the take-up torque, drawn above, is not electronic.
It is purely mechanical/magnetic. It has nothing to do with sensing when
the idler stops either, there is a separate electro-optical scheme for
that with led/photodiode and shiny segments on the bottom of one of the
gears in the idler train. I still don't properly understand how the
magnet thing sets a precise torque, but it does and it apparently not
adjustable in any way...
>U >I'm tempted to make up a cassette with a short loop in it, and see
>U >how well it works with zero take-up torque, as an experiment.
>
> May be informative. (where's the TRICORDER when you need it?)
OK, I did an experiment. I arranged for tape to come out of a cassette,
through a gap in the radio to the deck, along past the head, through the
capstan/pinch roller and then out again down onto the floor. So almost
no take-up tension apart from the weight of the tape to the floor.
After a couple of goes at getting it started, I find that it runs quite
happily in this mode, no tendency to ride up the capstan. (Tape does
rest against the _upper_ side of the little guide near the head, rather
than the lower one, but not pushing up much really.) Music playback
isn't perfect, but then there's no pad to press it against the head.
I notice that if I pull gently on the outcoming end, then if I pull it
slightly downward then the tape rapidly goes up the capstan. If I pull
it slightly upward then the tape runs down the capstan.
This does imply to me that the capstan/pinch roller are fairly happy
in themselves, though I suppose the angle could still be wrong and
only show up when the tape is being pulled by the reel.
> I lean away from the Capstan myself....I'm assuming you cleaned the
>Pinch rollers and removed any oxide brown film on the capstan shaft
>(created by tapes) by using alcohol/laquer thinner or scotchbrite.
The capstans, head, etc are spotless, cleaned with Electrolube tape
head cleaner (isopropanol I think) same time that I originally
replaced the pinch rollers.
> Since you say the problem is only on one side, that really points to the
> take up reel for that side & or the Idler assy you described in the PIC.
>
> With no power applied and no tape, feel the torque of both reels by
> hand and see if one feels significantly tighter.
Feels pretty equal to me. I think further investigation of the reel
on that side is required, though, maybe the reel height isn't quite
right (too low implied by the experiment) and I haven't yet dismantled
the reel hubs so there's more to investigate there. ;-)
> If not...it may be too slight to feel by hand, so, take off the snap
> rings and disassemble one reel at a time and inspect & clean the parts,
> lube the reel shaft(s) with light oil & check the end play when re
> assembled. Look for exessive play up/down.
The reel drive hubs that penetrate the cassette are spring loaded up,
so play oughtn't to be an issue. But maybe they are binding somehow
(there's old grease inside the up/down mechanism for the hubs...)
> IMO, look carefully when inspecting the reels...you may find some kind
> of binding there.
Will try here next!
> Good Luck,
Thanks!!
Mike.
P.S. Thanks to the others who've replied by posting and/or email too!
JackH35785
Projector Recorder Belt Corporation
Div. of Atex Corporation
10731 Gulfdale, San Antonio, Texas 78216
http://www.atexelectronics.com/PRB.htm
Regards,
Jack
Steve Herns
U >My gut feel is still that the torque is too high rather than too
U >low, if that were the problem at all. The tape certainly doesn't look
U >as if it is becoming slack at all, more that it's too tight at its top
U >edge going past the capstan. See experiment below.
I assume you've tried other Tapes, ranging from small (T-30) to Large
(T120)??
Also, look at the Tapes when you put them in. See if one side looks
raised higher up than the other side thats pulling good.
U >The thing that sets the take-up torque, drawn above, is not electronic.
U >It is purely mechanical/magnetic. It has nothing to do with sensing when
U >the idler stops either, there is a separate electro-optical scheme for
U >that with led/photodiode and shiny segments on the bottom of one of the
U >gears in the idler train. I still don't properly understand how the
U >magnet thing sets a precise torque, but it does and it apparently not
U >adjustable in any way...
Heh.
Guess its different than what I thought. I do seem to remember
working on something similar to what you describe.
If it controls Take-up torque, then it may be a suspect too.
But I still have my doubts there...theory being if it works spinning one
way, it should be ok going the other.
U >I notice that if I pull gently on the outcoming end, then if I pull it
U >slightly downward then the tape rapidly goes up the capstan. If I pull
U >it slightly upward then the tape runs down the capstan.
Also, I dont know if you checked the head alignment. Usually there's
a slotted screw to adjust the head slightly. Sometimes the Heads have
a built in U-shaped guidepost the tape travels through...that could be
socked up/down too much, causing the tape to ride up. Have seen it
happed lots of times.
U >> IMO, look carefully when inspecting the reels...you may find some kind
U >> of binding there.
U >Will try here next!
Either That, or check the Head alignment with the u-guide if it has one.
When this causes it, its tuff , cause by then usually a lot of time
has been put into something a slotted jewlers screwdriver can fix in
1/2 second. :^/