Film-Tech Forum ARCHIVE: USL JFM-20 Format Module switching randomly

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Posted by Michael Schaffer (Member # 1204) on 12-16-2006, 09:15 PM:

This problem is a little puzzling: I have two auditoriums here in which the format module JFM-20 switches randomly back to non-sync while playing a movie.

It happens pretty regularly, but not at defined points (e.g. cue positions), and it also happened after I had disconnected all automation connections to rule out automation misfires.
We also took out the cards, cleaned the contacts and reseated them.

It looked for a moment as if that had taken care of the problem, but it returned very quickly.

You can see the backlight of the non-sync button flicker nervously before it actually switches over (when the button is then lit contuinuously, of course).

It *appears* that the flickering is related to the sound level (i.e., it gets more nervous the louder the level gets), but I haven't had an opportunity yet to test run it with the audio inputs disconnected one by one.

Obviously, even if it turned out to be the cause of the problem (audio lines crosstalking onto the automation inputs), that wouldn't be the solution because the movies are so much more fun with the audio connected...

I am starting to think about a solution with a latching relay holding down the formats, but I would rather find the actual cause and appropriate solution.

I already talked to the nice people at USL and we discussed that problem, but it does not appear to be caused by a malfunction of the module - which I replaced with a brand new one recently anyway.

Posted by Mark Gulbrandsen (Member # 72) on 12-17-2006, 02:41 AM:

What happens if you leave the present automation lines disconnected? Also what automation unit do you have? Have you tried a new power supply in the JS and do the present power supplies have the power backup button still on them(a very bad thing!)? Have you tried running the processor only from another circuit perhaps in another booth?

Posted by Michael Schaffer (Member # 1204) on 12-17-2006, 03:25 AM:

It's hooked up both to the Christie DCA21 and the CFS automation, but I have already disconnected both (one at a time, and both together), and it didn't change anything.
The power supply is also fairly new, and to be doubly safe, I also swapped it with another unit which doesn't have that problem.
But it didn't make a difference either...

What puzzles me the most is that you can see the non-sync button flicker nervously, apparently coupled to the intensity of the audio signals. That's why I am thinking the signal may be crosstalking somehow onto the format switching circuits, after all, they are on the same card.

Posted by Gordon McLeod (Member # 33) on 12-17-2006, 08:48 AM:

Probably the powersupplyI have one that mutes itself for no reason until bypass is pressed

Posted by Mark Gulbrandsen (Member # 72) on 12-17-2006, 12:39 PM:

I'm thinkin more an open or almost open neutral since the lights modulate with the volume level... but the power supply is also a good thing to check. If there is a power bypass buton be sure to clip it out and bypass it... all of them eventually fail.

Mark

Posted by Gordon McLeod (Member # 33) on 12-17-2006, 01:46 PM:

Meaasure the voltage rails when this is happening in respect to the E terminal on the back plane and to real earth and see if the ground is floating inside the unit

Posted by Michael Schaffer (Member # 1204) on 12-17-2006, 02:12 PM:

That's a good tip. I will check that. I have already replaced the power supply recently (see above) because these are most often the cause for such funkiness, but that doesn't mean that the ground couldn't be lost somewhere else. Although the format module itself is pretty new, too.
Basically, switching occurs when any of the respective inputs are grounded. I guess that means that there must be a low voltage present on the automation inputs of the processor (maybe 5V or so) and the format module senses when that voltage disappears to ground and then switches. Or how does that exactly work?

I want to find out what the cause for this problem is, but it seems to me that in the meanwhile, using a latching relay to hold down the inputs permanently might be a good intermediate solution. Right now, we have the active format button taped down...
My idea is to use a low voltage, say 12VDC, dual coil latching relay (a single coil one is too complicated because you have to flip polarity) with a small transformer, connect the 0V line directly to the 0V contact of both coils, then route the 12V into the common line coming from the automation and hook up the automation outputs to the set and reset inputs of the two coils. That way, each time the automation pulses a format, the respective coil should set or reset the relay because the 12VDC will momentarily pulse from the transformer through the common line to the automation and out from the momentarily closed automation output to the + side of the respective coil.

Or are there any objections against such a solution? I don't think the automation would be damaged by those 12VDC pulses, would it?

Posted by Gordon McLeod (Member # 33) on 12-17-2006, 05:03 PM:

The terminals are usually held high and the automation pulls them low
I believe there are opto isolators on the format board that isolate it from the real world