[ Jim Quashnock wrote in 160711 MMDigest --

> I am having a difficult time getting the Theme Zero Setting
> soft enough.

Jim, I'll take a shot at this -- refer to the attached drawing.
I can think of three possible problems; there may be others, of
course, but these seem to be the most likely to me.

1. The knife valve connecting link has become dislodged from its
attachment point on the movable board.  With a fingernail you should
be able to feel that the hook of the link is correctly seated in the
groove of the wooden block.  If it isn't, it should be a relatively
easy task to remove the movable board fabric cover, and re-seat the
link, then replace the cover, making sure the external metal strap
is in place at a right angle to the groove to keep the link seated.

2. If the link is okay, next check the tightness of the lock screw
(#8 on the diagram) on the shaft.  I usually replace this screw with
a socket head (hex) screw as it allows me to apply torque-only forces
to the screw when tightening it.  Since you said higher vacuum level is
still present when trying to set the zero level, this is a less likely
cause.

3. There's a chance that the "dog" (#2 on the diagram) that moves the
knife valve as the shaft rotates is mis-positioned on the shaft too
close to the sliding portion in such a way that it "cocks" the valve
(#5) away from the block with the port (#4).  This can also be
diagnosed by removing the fabric cover and inspecting the area to
insure there is parallel contact between the two surfaces and the
phosphor-bronze leaf spring (#3) is correctly seated.

I see no reason to disassemble the box for these three possible causes.
Good luck!

John Grant

 [ http://www.mmdigest.com/Attachments/16/07/12/160712_071255_Duo-Art%20Knife%20Valve%20Assembly%20(Annotated).jpg