Fader Testing Procedures

Fader Testing Procedures

Several software tools are available to assist with exercising and evaluating faders.  Consult the Diagnostics section of the Flying Faders manual for more details and complete syntax:

TEST MOvefaders +/-xxx  [range of faders to test] initiates a move of faders to the dB value of plus or minus xx.x dB.

TEST Faders [range of faders to test] runs a sequence starting with random moves of all faders, followed by a ‘teeter totter’ anchored at the fader position NUMFAD/2, followed by a quick flip of each fader in sequence over the full range of faders twice, then random mix-like moves with the lights sequencing up and down along with each fader.

TEST SPeed GRaph [range of faders to test] executes full speed flips of the fader in each direction and graphs the result, showing the slopes and any overshoot.  The display also shows the overshoot, undershoot, and times required for the fader to be close to the final value and very close to the final value in each direction.  Excessive overshoot can be caused by a loose drive cord or excessive lubrication causing hydroplaning of the slider fingers at high speed.  A range of faders can also be graphed one at a time.

TEST SLIP is used to test for string slippage on the motor capstan.  The test begins with Fader #1 moving slowly from bottom to top of the fader to generate a software table of dB to position  conversions.  (The computer normally doesn’t know the physical position of the fader slider since the hardware ROMs interpret all dB values sent to the hardware to determine the appropriate position of the fader, depending upon fader taper and panel markings.)

Next, all faders are moved to the center of the fader stroke.  This test reverses the normal logic of the touch sense circuits, which normally turn off the motor whenever a fader is touched.  For this test, touching a fader knob activates that channel’s servo to hold the fader at the middle position.  Pushing the fader knob up and down provides a test for any loose drive cords.  If you can hear a motor begin to spin at high speed when you try to force the fader in one direction or the other, the cord is slipping.  Test each fader.

TEST Friction 1 [range of faders to test] is used to evaluate the ‘slipperiness’ of each fader in each direction at 20 points across the stroke of the fader.  The test may begin with the generation of a software table as described above if no prior test has already built the table.  If the table already exists from a prior test, the fader will be positioned at the bottom.  A short burst of power is applied to the motor and the amount of coasting is measured.  The farther the fader moves, the better the ‘slipperiness’, indicating good lubrication and low friction.  The test displays a table of the 20 values for the ‘up’ (/) direction and the 20 ‘down’ (\\) values.  Larger values are better.  The values for the downward stroke are typically larger than the upward stroke because of the direction and geometry of the slider contact fingers.  The values near the end are typically smaller due to the patented cord-tightening feature of the Flying Faders design.

Since there are several variations of fader construction, there are no hard and fast performance limits for the above tests.  The data presented by these tests is best used for comparisons with a set of reference data taken when the faders have been freshly serviced.  This will show any degradation before it becomes a serious problem.

A handy tool for testing faders is shown below.  This power supply can move the fader slowly along the track to check for smoothness, or it can be used to slam the slider against the end stop to check for drive cord slippage.

Fader Tester Schematic

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