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! ;-)

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Jim Adney
Madison, WI 53711 USA
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