jeremyabel wrote: ↑
Thu Mar 23, 2017 8:15 pm
Could you provide a photo of the one on your machine? It sounds like the sort of thing I could make with some sheet acrylic and a laser cutter.
Sorry... we haven't had these machines since we converted our plant from analog to digital nearly ten years ago. But yes, you should be able to make it pretty easily. Imagine a roughly triangular piece of plastic, perhaps 3/16" or 1/4" thick, where the base of the triangle is about an inch and a half, and the other two sides are four or five inches. Round off the corners to perhaps 1/4" radius, and hollow out the base (that is, the short side) a bit so it's slightly concave. Drill a hole in one of the base corners just slightly larger than the diameter of the studs on the card, staying far enough from the edge so that you don't just break off the plastic. Come to think of it, you would probably have better success machining a piece of aluminum -- after all, you aren't going to be pulling cards when the machine powered on. At any rate, the exact design really isn't critical: all it's doing is grabbing the stud on the board, and using it to pry the card out, against the left side of the frame.
I've had experience using a GVG DPM-700 which is a similar machine in purpose at least, but that seems to be a bit more... well-designed than the A51! I noticed the wire-wrapping on the backplane, connecting the boards together, and the fun fact that I get to make my own cable for the keyboard because it's a DB15 to DB9 situation of all things. Although maybe mine isn't indicative of the later models, as it's serial number 66, which I imagine is pretty early?
Do you have an A51, or an A51+? The plus version is a refinement, and there were quite a lot of pre-plus version frames out there.
Is the A51+ a single-channel system despite having connectors for 2 channels? There's nothing in the startup status screen that indicates whether it has a 2nd channel, and I'm waiting on cable-making supplies so I can't hook the keyboard up yet.
Abekas designed system to be modular functional blocks. A single A51 chassis -- which is what you seem to have -- is a single-channel DVE. You can build it up to a four-channel DVE by adding more A51 chassis, plus a video combiner chassis and a control combiner chassis. The video combiner receives the output video and key video from each A51 chassis, and produces a combined output video and key signal that is the coordinated composite of what the different channels are doing. It keeps track of the order of layering, so that you can build three-dimensional objects that have sides appearing and disappearing appropriately as the object rotates. The control combiner pretty much simulates a keyboard from the point of view of each channel; the operator's keyboard plugs into the combiner, allowing one keyboard to provide unified control over as many channels as it acquires. (If you have a facility with several control rooms, you can plug several keyboards into the combiner, so that each room can use different channels at the same time.)
Another option was expanded input switching for each channel. Each chassis itself has two inputs, and if you squeeze the picture down a bit and spin it around, you can have it automatically show input A on the front side and input B on the back side. (This applies only to flat planes... if you want to do this with an effect like a page turn, it takes too channels.) The expanded switching option let you connect two DiTech dual-level switchers to the chassis, one switcher to the A input, the other to the B input. One level of the switchers handled input video, the other handled input key. With expanded switching, you could build an effect that would automatically cycle through different video feeds every time your object spun around.
As you might imagine, a system with lots of options wound up taking up a fair amount of space. We had a two-channel system with external switching, and between the two A51 channels, the two combiners, the four DiTech switchers, and three frames of Grass Valley distribution amplifiers (many of them with built-in equalized delay lines), the DVE alone took up a full rack.
Which reminds me: it's important that the A and B inputs feeding the DVE be matched in both horizontal and burst phase, and that they be locked to the same reference as the A51 channels themselves. The DVE's analog-to-digital converter locks to the incoming video in much the same way that a frame synchronizer does, but the problem arises if you have an effect that causes the chassis to switch from one input to another. If the two inputs don't have matched horizontal phase (or worse, vertical timing), the picture is apt to jump at the point of transition. If the two inputs have different burst phase, you will be treated to a fraction of a second of rainbow colors until the ADC's clock gets locked to the new source.
All of this sounds like it should be a nightmare, but the truth is that I really liked the system. About the only maintenance it needed over the years was occasional replacement of the NiCad batteries on one of the boards (if the batteries go bad, it will forget its programming when the power goes off... including settings like video levels and timing). We also had a keyboard voltage regulator die after a director gave it a Pepsi challenge.