Tek 577 Step/OffSet Ampl Switch (cam switch) Strange behavior

[rodd]

Hi folks,
I am working on the step amplifier of this instrument and I found a very strange behavior of this switch (S404).
This is one of those cam switches used in many Tek instruments
The voltage set part of the switch is showing a resistance much different from the one expected ( using diag 4 as reference).
I removed the aluminum cover of this switch and inspected the gold fingers.
All fingers are there and move as the switch is rotated.
I  have sprayed Deoxit gold on the contacts (fingers)  and gently slided a sheet of paper when each finger was closed in an attempt to remove any dirt.
Then I measured the resistance between pin 6 of U360 (signal input) and pin 3 of U380 (signal output of the resistor divider) and compared with the expected value.
Note ( measurements taken with U380 pulled out)
The differences vary between 30% and 1/4 of the expected value.
I could not think of an explanation to such behavior.
Here are the values I have measured as well as the expected values:
Knob Volt reading(V)     measured resistance     expected value
         2                                           1.367                      1.505
         1                                           2.517                      3.01
       .5                                            4.317                      6.02
       .2                                            7.61                       15.05
       .1                                           10.18                       30.1
       .05                                         12.26                        60.2

I am attaching the reference diagram for reference
The measurements in question are related to the Voltage Set Resistors, on the top left part of the diagram.
Any ideas?

[m k]

So expected div 10 from .05 to .5 and 2 sets and then div 2 inside a set.

Parallel 15 all the time is pretty close but no idea how it can happen.

[rodd]

Thank you for your reply, m.k.

You figured it out!!!!
There is a circuit in parallel with the voltage set resistors that I have overlooked.
Please see the attached schematics.
The total series resistance of this circuit is R364+R393+R391+R396 = 6.2k+2k+1K+7.5k = 16.2k

Roger