Hi Again Dennis,
Some photos and some hints:-
The screws at the end-plate (behind each changer-finger) are used to open notes and lowered notes. I think these are the screws you are referring to, so I'll explain as clearly as I can what they do.
In the photo below, you are looking straight down on the E9th changer. The string ball-ends are the brass fittings on the steel-pins on each changer-finger. The leftmost string is the lowest note (B) and is string 10, the rightmost string is the high F# (string 1).
At the bottom of the picture are the screws which stick out at the end-plate. These tune one of two possibilities; either they tune a string which is raised only, or they tune a string which is lowered only.
In the photo you can see the threaded end of each screw touching most of the changer-fingers, but not all of them. First, on my steel, string 7 has no lower or raise on it, so the changer-finger just rests against the end of the screw and the open note is tuned by the tuning-key, which is intuitive. Once it is tuned, it's tuned and it's not going anywhere. But most other strings are either raised or lowered, and that's where these screws can become involved.
Here's basically how pull-release on a Marlen works (and we are assuming that it was been correctly set up initially and was more or less in tune). Let's also be clear about terminology. "Tuning" means bringing notes to their required pitch. "Setting-Up" means the initial process of adjusting the mechanism so each pedal and lever has enough travel to allow each string to be correctly tuned. Before tuning a steel-guitar, it has to be correctly set-up. We are talking about "Tuning" now.
To raise a string, a pedal (or a lever) is activated. This motion is transferred to a bellcrank on a cross-shaft, which rotates slightly. Attached to the bellcrank is a rod (the "raise-rod") which runs from the bellcrank to one of the holes in the changer-finger, where it is secured by either a collar and set-screw, or a plastic hex-nut called a tuning-nut.
As the bellcrank pulls on one end of the raise-rod, the the other end of the raise-rod pulls the changer-finger away from the stop-screw which it was resting against, and therefore the pitch of the note rises.
This is really important:- "A raised note is tuned by the tuning-key at the keyhead-end of the guitar."
Once the raised note is correctly tuned, the raise is released and the open-note (i.e. un-raised note) is tuned by adjusting the screw at the end-plate, because now the changer-finger will be at rest against it. If you run the screw in slightly it increases the pitch, and if you back the screw off, the pitch decreases. You DO NOT tune the open-note on a string that has a raise only on it with the tuning-key! You tune it with the screws behind the changer.
So, setting up a string which is raised only is a matter of repeating both processes until the raise is tuned and the open-note is also correct. Pretty straightforward.
A note which is lowered only is also tuned by these screws at the end-plate, but now you have to find a way to hold the changer-finger away from the end of the screw for the open-note.
This is usually done by a rod attached to a spring under the keyhead end of the guitar, running through a hole in the changer-finger, just like a raise-rod. To apply tension, the end of the rod protruding through the hole in the changer-finger is threaded and has a plastic tuning-nut on it. Let's call this a "Tension-Rod". Below is a shot of the ends of the tension rods and the tension-rod springs on my Marlen D10's E9th neck.
A way to prevent the tension-rod rotating must be found (so the tuning-nut actually advances or retreats along the thread and thus increases or decreases tension on the string via the changer-finger), and usually this mechanism is also used to achieve the lower by simply over-riding the tension set by the tuning-nut so the changer-finger moves backwards until it touches the end of the screw.
Running the screw in or out tunes the lowered note, which leads to the following observation:-
"A lowered note is tuned by the stop-screw at the end-plate of the guitar."
But you still have to tune the open-note. Once the lower is tuned, the open-note is fine-tuned with the plastic tuning-nut (not the tuning-key!) Each step is repeated until the lowered note is true and the open note is likewise true.
By the way, on earlier Marlens, there was no tuning-nut for lowers on the knee-levers (a stop-collar was used instead), but the amount of travel of the lever itself was adjusted under the guitar to tune the lowered-note. Depending on when it was made your guitar may use that method rather than a tuning-nut.
Once you get your steel upside-down and begin pushing on a pedal or a lever and seeing how the mechanisms actually work for raises and lowers, this will all fall into place.
Strings which are both raised and lowered (typically strings 4 and 8 on the E9th neck) require a little more complexity, usually involving a third tension-rod for tuning the open-note.
String 4 is the most complex, because it is usually raised by both a knee-lever (E to F) and a pedal (E to F# via pedal 3)as well as lowered by a knee-lever (E to E flat), but that is perhaps for another post at another time.
Here's one thing to keep in mind about pull-release in general:- this mechanism was designed for the relatively simple copedents of the 1970s. It handles any of them just fine, but trying to add splits and half-stops starts to get a bit more involved. Back in the 70s the standard E9th tuning was 3 pedals and 4 knee-levers...and that's all people like Lloyd Green, Hal Rugg and Weldon Myrick needed to play some of the greatest steel of the era which still sets a benchmark today.
