The page describes modifying the circuitry of a camera, the risk of doing this is all yours, do not attempt this if you're not proficient at electronics.
Do you still use one of the 1990s-vintage Panasonic WV-F15 cameras, and want the tally lights to work, but don't have the CCU attachments for it? This page details how you can do that.
As far as I can tell, the only way to activate the tally lights is when you have the WV-AD37 RCU adaptor on the back, and the attached RCU. The tally appears to be multiplexed with the serial control system, it's not a separate wire that you could put a signal into. Likewise, most of the control signals are time-multiplexed, it's not like the old CCU cables with one wire per function.
Looking at the 32 pin header at the back of the camera head (when there's no back on it), there are notes that say the second pin down on the left side is a combined tally and serial clock line, but there's nothing I've managed to do that would activate the tally light through it. Other notes just list that pin as a serial clock line (for the control signal multiplexing). Which leaves you with two alternative options to have working tally lamps:
Either, attach external lamps, and drive them independently of the camera. This is the easiest approach, though not the tidiest (more cabling), and lengthens the set up time if you take these cameras out on location shoots. Though doing this does offer advantages; the existing tally lamps on the WV-VF65BE aren't that great, you can put tallies on that are far better than the originals. The tiny LED next to the viewfinder screen can disappear into the cameraman's eye's blind spot, depending on where they're looking (I've been caught out by that a few times), so you keep on looking back and forth between screen and tally light, it gets hidden by the viewfinder hood when panning and tilting, and it isn't very visible under bright lighting. The front tally can only be easily seen from the front, which puts your floor manager, and the rest of your cast and crew, at a disadvantage. It has annoying turn-on and turn-off delays, which keeps your talent looking at the wrong camera, after you've switched away from it, and doesn't let them know which camera to turn to, for a moment or so (changing C11 on the viewfinder's power board, to a smaller value, can shorten this delay). And it's cumbersome to change the camera numbers that are placed inside the tally light housing.
Or, modify the interface between the camera head and the viewfinder, on the WV-Q39AE mounting bracket (amusingly mislabelled as “blacket” on our unit). It has circuitry that monitors a combined vertical pulse, zebra, and tally line from the camera head, and sends an isolated tally signal to the viewfinder. You can interupt its output to the viewfinder, and put your own tally input socket into this interface box.
What we did, was remove the genlock back-end from the camera, replace the custom 10-pin connector with a common CCJ 10-pin connector (as has been used on small video cameras since the 1960s), and connect its tally line to a socket newly added to the genlock back. Then we modified the viewfinder interface on the mounting bracket, adding a socket so we could patch it directly to the genlock back-end, and inserted a buffer circuitry between the new tally socket and the wiring leading to the viewfinder's tally input. The patch lead between the back-end and the interface only needs one wire, so simple banana connectors will suffice. And we've fitted a second red LED into the plastic frame under the screen, where it's easier to notice under various different filming conditions.
Modifying the viewfinder interface
Remove the interface box from the bracket, and locate the header for the socket leading to the viewfinder; snip the wire furthest away from the socket, half way through the length, and insulate the end coming from the circuit board header plug. This is the tally wire, you're going to make use of the wire leading to the viewfinder socket. If your mixer supplies 5 volts when the tally is on, and 0 volts when off, you could connect it directly to this wire. But, if your mixer works how most do, with either an open circuit collector output, or mechanical relay contacts output, which grounds the tally wire when on and leaves it open circuit when off, you'll need to build an interface.
A simple solution is a NPN transistor, four resistors, and a diode. String a couple of 3 kΩ resistors across the 9 volt regulator on the interface circuit board, to give you a 4.5 volt source to turn on your viewfinder's tally light. This 4.5 volt source will be fed to the tally input, with the collector of your transistor across it to pull it down to zero volts when the tally should be off. The emitter will be connected to ground, and the base to your vision mixer's tally output, via a 10 kΩ resistor (buffering), and the diode (isolation), with a 10 kΩ pull-up resistor to the 9 volt supply between the diode and the transistor (this keeps the tally lamp off until the mixer pulls the line down to ground). And that's the entire circuit, there's a diagram further down this page. There's enough room in the bracket to fit that all on a small circuitboard and place it inside (insulated, of course). For the transistor, I used a spare BD139 that I had in the parts box, it's extreme overkill for this circuit, but it's a common part, and very unlikely to get damaged by electrical noise created from your tally line being dragged across the floor, it's a tough transistor.
If your vision mixer tallies share a common ground with the video wiring, you may only need one wire to the interface (it's a very low current, and shouldn't cause any glitches). But if it's an isolated ground, then run a wire from the mixer's common to the interface's ground. I used ordinary shielded audio wire between the mixer and the interface to carry the tally and ground wires (this should stop electrical noise being a problem, and give some protecton against problems caused by static electricity from dragging a cable across the floor). And installed a small socket into the bracket to attach the wiring. I used a 3.5 mm stereo jack, wiring up the tip and ring, leaving the sleeve alone, so it's not electrically connected to the chassis. If you use a switched socket, you can arrange it so that when this socket is disconnected, the original tally wiring is used instead of your modifications.
Starting from the viewfinder socket end, the 6 pin header leading to it carries the following signals:
- +12 volt supply (red wire)
- Video signal (white wire)
- Shield for video signal (black insulation)
- Supply ground (black wire)
- Standby signal [+5V standby/0V operate] (yellow wire)
- Tally signal [+5V on/0V off] (orange wire)
NB: I don't know if your wiring will use the same colours as in our unit. Count the pins, and measure the signals.
This is the circuit diagram, it's about as simple as it could get, the parts were chosen out of my spares. You could use a smaller, and cheaper, transistor; its output only has to deal with low current (another transistor buffering circuit). The BD139 has the advantage of being quite robust, and it's easy to tell which leg is which. And, if you wanted, you could use one to directly drive a tally lamp on the back of the camera, which would be much more obvious to the cameraman than the piddly little LED on the back of the viewfinder (which may be in your blind spot, while you're looking at the viewfinder screen). We took the plastic frame off the screen, and installed another LED in the centre of the frame, below the screen. Having another tally light gets around the tally disappearing in your blind spot problem. And putting it that position means that you can always see the tally light, even when doing long pans or extreme tilts.
The diode is for isolating this tally input from others, if you were to have one tally output from your mixer drive several tally inputs (such as the camera and the preview monitor, in the control room). Without it, the 10 kΩ resistor to the transistor base, and the transistors base-emitter junction, can pull the line down enough to turn other tallies on (together, they act like a 10 kΩ resistor and diode, in series, to ground). It's just an ordinary small diode, something like a 1N4001, or most small signal diodes (e.g. 1N914), should do, it doesn't really carry much current. It can be omitted if you're not tying multiple tally inputs together.
If you have the simpler WV-Q39 bracket's viewfinder interface circuit, which has less transistors, doesn't mix in the OSD characters, and uses a 5 volt regulator, then omit the bottom 3 kΩ resistor, completely. You want the collector to go fully up to the 5 volt supply rail when the transistor is not conducting, and all the way down to ground when it is.
The tally output stages of video mixers will usually either be relay contacts, or a similar looking circuit to the above, albeit minus the 3 kΩ resistors. If its a transistor output, its collector will be open-circuit. The thing that connects to it, your camera, will form the rest of the collector circuit.
This is a picture of the WV-Q39AE bracket's interface opened up. The new tally interface is inside the green heatshrink going off the top of the picture, and will simply be placed into the space inside the box. The orange wire at the right is the interrupted tally line. The jack at the top right is the multipin leading to the viewfinder, next to it a 3.5 mm jack has been installed for the tally input. The cable at the bottom left leads to the camera viewfinder socket. The red and blue twisted wires are the power to the tally interface, and the grey and yellow wires are the tally in and out of the tally interface.
If you have cameras that might be connected through a CCU sometimes, as well as being used stand-alone, you may wish to put a switch into the interface box, so you can use the camera's tallys with the original design, or the modified one. The simple solution, of using a switched jack for the modified tally, that would automatically change back to the original circuit, when nothing is plugged into it, is difficult to implement, though not impossible, because the interface box is so small, and few small jacks have completely independent switches from their connectors. Another option would be to design your circuit with a diode-coupled output, and another diode from the output of the original circuit, and join them together to the monitor (as a diode OR gate).
Interestingly, this circuit shortened the turn-off time of the front tally lamp. The original interface circuit probably had a lighter resistance, so the viewfinder tally input took longer to discharge. The (original) turn-off delay seems to be a combination of Panasonic's interface circuit (with a 10kΩ & 10µF RC integrating circuit—the tally is a DC bias over another AC waveform), and the lamp driver in the viewfinder. There's a deliberate soft turn on built into the viewfinder, so the viewfinder don't glitch as the lamp fires up. But I don't know why they'd deliberately make the lamp turn off so slowly. You can change the lamp on/off delay by changing C11 on the circuit board behind the tally lamp. I found about 2µF to be a good compromise, instead of the original 10µF. The rear LED tally switches instantly.
Overall, the tally signal has to pass through several stages: Tally input at the CCU is multiplexed into the serial data control (potentially delaying transmission by one field of video, if the tally came on after the tally line had been polled, plus whatever routines happen inside the custom microprocessor). The serial data controls pass through the microprocessor, and whatever routines happen inside it may be a cause of delay. The tally output comes direct from the microprocessor, while other control signals are converted to an analogue signal, and demultiplexed to several buffer amplifiers. The tally signal goes to the interface on the bracket between the camera head and viewfinder, which has an RC circuit to separate the tally DC signal from an AC waveform it shares a control line with. The signal goes into the viewfinder, which uses an RC circuit so the tally lamp has a soft turn-on and turn-off.