Film-Tech Forum ARCHIVE: Dolby DA-20 control problem.

This is topic Dolby DA-20 control problem. in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Stephen Furley (Member # 1277) on 04-30-2015, 02:36 PM:

Had a few hours between shows today, so thought I'd have a go at installing a DA-20 that I've had for a while. Unit is connected to a CP-65 via an existing DMA-8 plus using cables which I made up. No digital soundheads at the moment, but I have a (Cat. 708?) Dolby Digital Signal Simulator which I can connect to either of the digital soundhead connectors on the DA-20 to provide a signal. Also, no motor start relays, but the connections are brought out to two pairs of wires which I can manually close.

Digital audio processing worked fine; LEDs show what I would expect, mainly using the 1 kHz. tone digital test signal into the projector 1 soundhead connector, and the test signals can be heard on the monitor speakers.

Closing either pair of motor start relay connections seemd to have no effect. Analogue audio from film still works fine, no problems there. The DA-20 cannot control the CP-65 format.

After a while everything suddenly starts working, with the exception that the DA-20 cannot switch the CP-65 into SR analogue format. There was a wire missing between the DMA and the CP-65; I've fixed that.

Everything then seemed fine, the digital test tone would play, if I switched that off the system would switch to playing analogue sound from film, and would switch back to format 10 when I turned the digital test signal back on.

The system powers up with the projector 1 LED on, and motor 1, Projector 2 and Motor 2 off. Closing the contacts for projector 1 brings up the Motor 1 LED, while closing the projector 2 contacts brings up Projector 2 and motor 2 LEDs. Closing the projector 2 contacts while projector 1 is running seems to make the unit try do do a digital changeover after a few seconds. The Digital and Analogue LEDs reflect the signal that is being played at the time.

Seems that everything is working fine, at least as far as it can be until I have soundheads and relays.

I was feeling quite pleased until the fire alarm was activated and I had to power everything down and get out for half an hour.

When I came back and powered everything up it had stopped working. The digital audio processing is still working fine, but the control problems are back. Closing the motor start relay connections has no effect, and no 'click' can be heard as it could when they were working. The DA-20 cannot control the CP-65 mode. Projector 1 LED is lit, but motor 1 and projector and motor 2 are unlit. The 'Digital' LED is permanently lit, and the analogue one is permanently unlit.

Powering everything down several times has made no difference. While powered down I tried removing and re-seating first the Cat. 611 A, and then all of the cards. Still no luck.

The DMA is still able to control the CP-65 format while the DA-20 is connected to it.

Any ideas what could cause this? If the 611 was faulty I wouldn't expect the fault to be intermittant. The fact that both digital changeover and CP format control have stopped working, and started working, at the same time seems to rule out a cable problem, and the fact that it worked for a while, after not working seems to confirm this. Tested all cores on all cables when I made them up some months ago, and they all tested ok. The processor type selector in the DA-20 is set correctly.

I have two other DA-20s in store If I need any spare parts.

Any suggestions as to what could cause this problem?

Posted by Stephan Shelley (Member # 8587) on 04-30-2015, 03:32 PM:

I am guessing that you have the Cat 611 set to CP-65 mode? The other thing that comes to mind is that the DA-20 when in CP-65 mode looks for the format 10 button on the CP-65 to be pushed. When you push it with no digital signal in the DA-20 it should jump back to format 05. After you have done that once the DA 20 gets a valid digital signal it should jump from format 05 to 10. It needs to see the format 10 button push to activate it.

There are newer 611 cards that do auto digital if set correctly but not from non-sysnc. These do not need the format 10 button push to activate but do need to be in a optical format.

Posted by Stephen Furley (Member # 1277) on 04-30-2015, 03:57 PM:

Thank you for your reply.

I am sure that it is in CP-65 mode; I checked that, and this setting has not been changed since it was working.

I have pressed the format 10 button, but later, to check that I could switch manually between analogue and digital audio. It might be worth trying to press it at the start. If this was the problem could it also cause the motor start signals to be ignored? It's almost as if the control system thinks the DA-20 is not being used, and disconnects it, though the digital audio is still being processed by it, and passed through the DMA to the CP-65.

No more screenings until Saturday afternoon, but I have to go in tomorrow to set something up; I'll have a play.

Edit, a few minutes later.

Thinking about what you wrote, disabling the control side of the DA-20 if format 10 was not pressed could make sense; if an analogue-only print was being played you wouldn't want any odd spurious signals changing things.

Posted by Stephan Shelley (Member # 8587) on 04-30-2015, 04:34 PM:

Try a different Cat 611 0r 611a the auto digital card.

Posted by Stephen Furley (Member # 1277) on 05-06-2015, 04:50 AM:

Swapping the 611A made no difference. Of course, I have no way of testing either card to be sure that it's not faulty.

I'm busy with other things at the moment; will take another look at it next week.

Posted by Stephan Shelley (Member # 8587) on 05-06-2015, 11:21 PM:

The DMA 8+ is in film mode? If it is not it blocks the control signal from the DA 20. Try bypassing the DMA 8+ on the control and see if it works properly.

Posted by Stephen Furley (Member # 1277) on 05-07-2015, 03:19 AM:

Yes, it's in film mode. I did try by-passing the DMA, still the same.

I was reading the DA-20 manual last night, and found a couple of things that I need to check. It's General Election today, and the town hall is being used for vote counting, so I won't be able to do anything today. There's a normal screening on Saturday and I need to go in to speak to the projectionist before the show so I may be able to take another look then.

Better luck with DTS; got the demo reel to run with digital sound. All a bit makeshift at the moment, DTS-6D on the floor because there's not enough room for it in the sound rack until some other things are moved around a bit, only one reader installed, and that just clamped in place on the projector with bits of wood and metal studding, but good enough to prove that the equipment works.

We're getting there, slowly.