The
EDI Mark VII has a control box called a "Multi LINK" depending on the number of dimmers that you have in the rack, there can be one or two
circuit boards in the box. Each
circuit board can control a total of 60 dimmers. A fully loaded
Mark VII rack if using 20 amp and smaller dimmers would be 120 dimmers. If the flickering occurs on all 120 dimmers, then there has to be something wrong with the signal from the
console, or really dirty
power in the facility. If the flickering only occurs on the first or last 60 dimmers but not on both, then it is in the control portion of the
circuit board such as the input data transceiver or cpu. If it is on only 1/3 of the dimmers on the
circuit board, then it is the zero crossing detector
circuit for that
phase of
power.
The multilink boards were developed before
DMX had a really good
foot in the door. They were developed to handle AMX192,
CMX, early
DMX and a patchpanel that allowed 10 channels of 0 to 10 vdc analog. As a consequence, the transceiver chips are for RS 422.
DMX will operate on RS 422, but not as reliably as on RS 485. The transceiver chips for RS 422 can be damaged if
power is applied to the device dending the data before the receiving device, or in this case the multilink controller. When I arrived at our
theatre about 8 & 1/2 years ago, our
Mark VII was having to be repaired several times a year. I modified the input to the multilink boards to use the 75176 RS 485 data tranceiver chip. I also put a
relay that was normally open on the data
line. The
relay made contact for the data when
phase A ( the main
power for the multilink) was turned on. This in turn kept data off of the input Tranceiver until it was powered. I also installed
power surge protection on each of the three phases going into the multilink. In the last 8 years we have never had a failure. The
Mark VII is a good solid rack, but it was designed a little early in the
DMX cycle. I understand that getting service on the multilink boards is near impossible. In reviewing the schematics for those
circuit boards, everything is still available at a component
level, except possible the CPU and the ROM with the main software. The board is much more complex than it needs to be in order to support the different inputs and formats.
I don't know that this is information that will help you much, but it might help you to understand what to look at by establishing patterns to the troubles that you are having, and from there you can possibly narrow it down for servicing.
