I have a question about my Sony SL-2000 Betamax VCR; that's the little
1982 portable that is the mate to the TT-2000. It's not clear to me
where the best place to ask this might be, so I'm going to start by
just asking here. Just in case, does anyone know if there is a Beta
VCR newsgroup?

My SL-2000 works just fine except in Rewind. While rewinding, the tape
gets loose and flops around until the RH reel slows down and then the
tape goes briefly tight speeding up the reel. This repeats over and
over again. It didn't do this when the deck was new, and I'm sure this
isn't good for the tapes.

Fast forward works just fine.

My impression is that there should be some very mild back tension on
the RH reel when rewinding, but I can't figure out how this should
happen.

I have the service manual, but no VCR servicing experience. I've had
the tape deck all apart and even disassembled the motor. There are no
tension bands in the design, nor are there any friction pads or
washers. My guess is that the braking must be done electrically, but I
don't understand the drive circuitry well enough to know which parts
would affect this.

The motor control is all done by a microprocessor, and the manual is
not clear on what the states of the different lines should be during
rewind. (I'm not clear on this; it's been years since I last looked at
it....)

I fixed a couple of cold solder joints in the matching camera a few
years ago, but those were all for leads which were obviously added by
hand after the machine soldered boards were produced. There's nothing
in this area of the board that looks like that might be the cause of
this problem.

I'd really like to fix this, but I need some advice to get me started
in the right direction.

Thanks for any advice you might have to offer.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

On Wed, 29 Dec 2004 19:28:14 -0600, Jim Adney
wrote:

I have a question about my Sony SL-2000 Betamax VCR; that's the little
1982 portable that is the mate to the TT-2000. It's not clear to me
where the best place to ask this might be, so I'm going to start by
just asking here. Just in case, does anyone know if there is a Beta
VCR newsgroup?

My SL-2000 works just fine except in Rewind. While rewinding, the tape
gets loose and flops around until the RH reel slows down and then the
tape goes briefly tight speeding up the reel. This repeats over and
over again. It didn't do this when the deck was new, and I'm sure this
isn't good for the tapes.



This is the right place for your question.

I have an SL-2500 which is the non-portable version of your VCR. It
also has the same problem you're describing. I think the problem is
caused by a worn upper head drum (the part that doesn't spin). The
extra friction seems to cause an oscillation in the servo system
that's supposed to keep the tape tension constant in rewind. I've
never bothered repairing it because I found another 2500 that was in
excellent condition to replace it with. I think the upper drum is
still available for not too much money (about $40). If you can see
wear marks where the tape passes over the drum, it wouldn't hurt to
replace it. These are excellent VCRs with no belts, tires, tension
bands, or other friction devices to wear out.
Andy Cuffe

These are excellent VCRs with no belts, tires, tension
bands, or other friction devices to wear out.

Well, except the upper drum that is!

(Tee-Hee)

Mark Z.



"Andy Cuffe" wrote in message
...
On Wed, 29 Dec 2004 19:28:14 -0600, Jim Adney
wrote:

I have a question about my Sony SL-2000 Betamax VCR; that's the little
1982 portable that is the mate to the TT-2000. It's not clear to me
where the best place to ask this might be, so I'm going to start by
just asking here. Just in case, does anyone know if there is a Beta
VCR newsgroup?

My SL-2000 works just fine except in Rewind. While rewinding, the tape
gets loose and flops around until the RH reel slows down and then the
tape goes briefly tight speeding up the reel. This repeats over and
over again. It didn't do this when the deck was new, and I'm sure this
isn't good for the tapes.



This is the right place for your question.

I have an SL-2500 which is the non-portable version of your VCR. It
also has the same problem you're describing. I think the problem is
caused by a worn upper head drum (the part that doesn't spin). The
extra friction seems to cause an oscillation in the servo system
that's supposed to keep the tape tension constant in rewind. I've
never bothered repairing it because I found another 2500 that was in
excellent condition to replace it with. I think the upper drum is
still available for not too much money (about $40). If you can see
wear marks where the tape passes over the drum, it wouldn't hurt to
replace it. These are excellent VCRs with no belts, tires, tension
bands, or other friction devices to wear out.
Andy Cuffe

Andy

I'm not familiar with particular deck but do have a fair bit
of Beta experience in general.

If this deck has a reel idler (Sony call it a pendulum), which
swings between the two reels, then I would suspect that it is
not pulling smoothly, causing the tape to speed and slow. Sony
idlers do not usually have friction surfaces to wear out, they
use a magnetic clutch which is fairly reliable. But what does
happen is the idler wears its way through the plastic mounting
it sits on. Sometimes the solution is as simple as adding a
washer under the idler to set it to the right height again.

For the other explanation suggested here, that the upper drum is
worn, there is an old trick which can extract more life from
these. The same applies to lower drums on VHS. You can gently
apply some longitudinal scratches into the stationary part of
the drum (ie along the length as the tape sees it) using
glasspaper. I know this sounds crude, but it does the same job
as the lines which are manufactured onto the head, it helps to
keep an air film between the drum and tape. As the drum wears
and is "polished" by the tape, these lines can fade away causing
the tape to stick to the head drum. The above is usually only
done as a last resort when the alternatives is to scrap the
machine, but can provide a complete cure to tape sticking problems.

Hope this helps,

Colin

Andy Cuffe wrote:

On Wed, 29 Dec 2004 19:28:14 -0600, Jim Adney
wrote:


I have a question about my Sony SL-2000 Betamax VCR; that's the little
1982 portable that is the mate to the TT-2000. It's not clear to me
where the best place to ask this might be, so I'm going to start by
just asking here. Just in case, does anyone know if there is a Beta
VCR newsgroup?

My SL-2000 works just fine except in Rewind. While rewinding, the tape
gets loose and flops around until the RH reel slows down and then the
tape goes briefly tight speeding up the reel. This repeats over and
over again. It didn't do this when the deck was new, and I'm sure this
isn't good for the tapes.




This is the right place for your question.

I have an SL-2500 which is the non-portable version of your VCR. It
also has the same problem you're describing. I think the problem is
caused by a worn upper head drum (the part that doesn't spin). The
extra friction seems to cause an oscillation in the servo system
that's supposed to keep the tape tension constant in rewind. I've
never bothered repairing it because I found another 2500 that was in
excellent condition to replace it with. I think the upper drum is
still available for not too much money (about $40). If you can see
wear marks where the tape passes over the drum, it wouldn't hurt to
replace it. These are excellent VCRs with no belts, tires, tension
bands, or other friction devices to wear out.
Andy Cuffe

On Wed, 29 Dec 2004 22:45:38 -0500 Andy Cuffe
wrote:

On Wed, 29 Dec 2004 19:28:14 -0600, Jim Adney
wrote:

I have a question about my Sony SL-2000 Betamax VCR; that's the little
1982 portable that is the mate to the TT-2000. It's not clear to me
where the best place to ask this might be, so I'm going to start by
just asking here. Just in case, does anyone know if there is a Beta
VCR newsgroup?

My SL-2000 works just fine except in Rewind. While rewinding, the tape
gets loose and flops around until the RH reel slows down and then the
tape goes briefly tight speeding up the reel. This repeats over and
over again. It didn't do this when the deck was new, and I'm sure this
isn't good for the tapes.

I have an SL-2500 which is the non-portable version of your VCR. It
also has the same problem you're describing. I think the problem is
caused by a worn upper head drum (the part that doesn't spin). The
extra friction seems to cause an oscillation in the servo system
that's supposed to keep the tape tension constant in rewind.

The fact that you have an SL-2500 which did the same thing is somewhat
reassuring. At least it suggests that this might be a well known
problem (at least to someone) and that there might be a known cause
and solution out there.

Forgive me, but I don't understand how extra friction in the upper
head drum could cause this symptom. [Doesn't the upper part spin? I
thought the lower part was stationary....]

The cyclic operation I see has a period of a little more than a
second. Surely any feedback servo would be much faster than this.

My assumption has always been that I'm not getting any back tension at
all. Since this is not in play mode, I was willing to guess that the
Rewind backtension was less important and that it was probably much
smaller, just to reduce wear on everything.

I keep thinking of the small AC motors we used to use at work. Braking
on those could be produced just by sending them some DC. If Sony did
that, then it MIGHT be that there is simply a resistor somewhere that
has gone open, setting the braking current to zero. For Rewind, and
FF, I'd expect just some small fixed amount of electronic braking. So
I'm thinking that the problem might be an open resistor, or a dead
transistor which switches it.

If I'm dead wrong here, tell me quickly. ;-)

Is there really a servo in play here in Rewind?

Rethinking this, I'm wondering if the feedback you're suggesting is
feedback to the LH reel motor, for drive speed. I had been assuming
that you meant feedback to the RH reel motor, for backtension.

One of the things I'd been toying with trying, was to see if the deck
will play while upside down. (Will it?) Then I could monitor that
board, which is on the bottom of the VCR, while it was doing various
operations. I figured that I could monitor the LH motor during FF just
to see what should be happening to the RH motor during Rewind,
assuming symmetry in the design. Is that reasonable? A comparison of
the voltages seen on each might help point out the problem.

The problem with this is that these are not just simple DC motors;
they are brushless (stepper?) motors, so I think it will take some
careful scope measurements to compare their inputs.

I'll check out the head drums anyway and see what they look like.

Thanks for the suggestions.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

On Fri, 31 Dec 2004 18:38:25 +0000 Colin McCormick
wrote:

If this deck has a reel idler (Sony call it a pendulum), which
swings between the two reels, then I would suspect that it is
not pulling smoothly, causing the tape to speed and slow. Sony
idlers do not usually have friction surfaces to wear out, they
use a magnetic clutch which is fairly reliable. But what does
happen is the idler wears its way through the plastic mounting
it sits on. Sometimes the solution is as simple as adding a
washer under the idler to set it to the right height again.

The SL-2000 has 2 separate reel motors. Each is some kind of stepper
with 2 drive lines and a common return, so 3 wires to each motor.
There are no friction surfaces or clutches, although there is a brake,
but I don't think it comes into play except when the tape comes to a
complete stop.

For the other explanation suggested here, that the upper drum is
worn, there is an old trick which can extract more life from
these. The same applies to lower drums on VHS. You can gently
apply some longitudinal scratches into the stationary part of
the drum (ie along the length as the tape sees it) using
glasspaper. I know this sounds crude, but it does the same job
as the lines which are manufactured onto the head, it helps to
keep an air film between the drum and tape. As the drum wears
and is "polished" by the tape, these lines can fade away causing
the tape to stick to the head drum. The above is usually only
done as a last resort when the alternatives is to scrap the
machine, but can provide a complete cure to tape sticking problems.

Sounds like you're describing "sticksion." Sounds plausable. I'll look
into that. You're the second person who seems to think that the upper
drum is stationary, so it sounds like it's time for me to get in there
again and refresh my memory.

OTOH, wouldn't such sticksion work in both directions? I get this
problem only in REW. FF works just fine.

I looked at the schematic last night and each motor has a common and
two winding inputs. The two winding inputs appear to be switched
between gnd and +12V depending on the mode. (Presumably, in one of
those states, it is actually switched by the motor controller IC.) The
mode for one motor depends on whether it is in FF or not, the mode for
the other depends on whether it is in REW or not. I think this is
where I need to look. It looks to me like this could be the source of
the electronic braking that my SL-2000 is lacking.

It might be as simple as one of those transistors being shorted (or
open) or it might be that the IC which controls them is bad, or a bad
component in between, or a bad solder joint, or....

Surely there is SOMEONE out there who has actually fixed this problem
before. Now's your time to speak up! ;-)

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

On Fri, 31 Dec 2004 22:07:58 -0600, Jim Adney wrote:
I keep thinking of the small AC motors we used to use at work. Braking
on those could be produced just by sending them some DC. If Sony did
that, then it MIGHT be that there is simply a resistor somewhere that
has gone open, setting the braking current to zero. For Rewind, and
FF, I'd expect just some small fixed amount of electronic braking. So
I'm thinking that the problem might be an open resistor, or a dead
transistor which switches it.

If so, it should be simple (if time consuming) to find the bad component
with a decent ($20 or so) cheap digital multimeter. You need one with
a "diode test" function to check the transistors.


--
| David Gersic |
| Doc's??? Oh, you mean the stuff we wipe up coffee with? |
| Email address is munged to avoid spammers. Remove the underscores. |

Jim Adney wrote:
into that. You're the second person who seems to think that the upper
drum is stationary, so it sounds like it's time for me to get in there
again and refresh my memory.

On betamax recorders, both the upper and lower drum are stationary. In
between is a small (adjustable, please do not tweak without proper
tools) gap, in which the head disc is placed.

---
Met vriendelijke groet,

Maarten Bakker.

The fact that you have an SL-2500 which did the same thing is somewhat
reassuring. At least it suggests that this might be a well known
problem (at least to someone) and that there might be a known cause
and solution out there.

The SL-2000, SL-2500, and SL-2700 essentially share the same platform, although
the SL-2000 is a portable top loader while the other two are relatively high
end front loaders, particularly the Hi-Fi SL-2700.

They all use a dual motor drive for the spools as opposed to a single motor
pendulum configuration.

Not many models used this configuration because of the expense.

Forgive me, but I don't understand how extra friction in the upper
head drum could cause this symptom. [Doesn't the upper part spin? I
thought the lower part was stationary....]

Both parts of the drum do not rotate. Only the inner head disc rotates. But,
grime buildup on the drum surfaces can cause excessive drag, which may cause
problems with the tape travel.

Another thing you can do is to check the condition of the threading mechanism
drive belt, which should be to the upper right of the drum. If the belt is
worn, replace it and see what happens.

Also check the condition of any and all braking materials on the spool drivers.

The problem with this is that these are not just simple DC motors;
they are brushless (stepper?) motors, so I think it will take some
careful scope measurements to compare their inputs.

They are servo controlled brushless motors with servo feedback provided by a
magnetic sensor. - Reinhart

On Sat, 1 Jan 2005 07:02:18 +0000 (UTC) David Gersic
wrote:

On Fri, 31 Dec 2004 22:07:58 -0600, Jim Adney wrote:
I keep thinking of the small AC motors we used to use at work. Braking
on those could be produced just by sending them some DC. If Sony did
that, then it MIGHT be that there is simply a resistor somewhere that
has gone open, setting the braking current to zero. For Rewind, and
FF, I'd expect just some small fixed amount of electronic braking. So
I'm thinking that the problem might be an open resistor, or a dead
transistor which switches it.

If so, it should be simple (if time consuming) to find the bad component
with a decent ($20 or so) cheap digital multimeter. You need one with
a "diode test" function to check the transistors.

Instruments are no problem. I've got a nice Fluke, several scopes, and
more. What i lack is time, and VCR experience, so I'm studying the
schematics and reading everyone's comments carefully. This sucker is a
real bear to take apart; there are more than a dozen PC boards in
there, all shoehorned in tight as a drum. To do any diagnosis, I may
have to solder in some tests leads, then reassemble and monitor my
leads while the VCR runs.

My thanks to each of you.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

If this deck has a reel idler (Sony call it a pendulum), which
swings between the two reels, then I would suspect that it is
not pulling smoothly, causing the tape to speed and slow.

This model uses two independent brushless motors for each of the spools. -
Reinhart

On 08 Jan 2005 19:33:33 GMT (LASERandDVDfan)
wrote:

This model uses two independent brushless motors for each of the spools. -

I think what you meant to type was that this model uses two
independent brushless motors, one for each spool. ;-)

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------