Dolby CP 650

[Neal Scanlan]

Hello,

I would like to use 2 projectors that run off the same platter.
I would like to use a switch to change between projector 1 and 2.
I assume that the existing jumper is removed but
I’m a little confused as to which are the correct pin connections to the 9 pin Motor Start.

Can anyone advise?

[Steve Guttag]

Pin 1 and 5 are for P1 Pins 5 and 9 are for P2. So, if you are going to make something up...connect pin 5 to a switch's "swinger" and pin 1 to one end and pin 9 to the other. Then you just have to flip the switch as you switch between the two. Alternately, go full old-school and just hook it up as a changeover system using a relay's coil in parallel with each motor (appropriate coil voltage) and use the normally closed contact of each ready to let the CP650 know which motor is running. Note, some projectors, like Kinoton, have spare "run" relay contacts/terminal blocks to provide this. You will have two wires on terminal 5.

You can't just remove the jumper as the CP650 has to see the "motor" running.

[Neal Scanlan]

Hello Steve,
Thank you for your help, another task solved.

[Steve Guttag]

It would have been nice if I gave you the proper information. On the relays, it would be the Normally OPEN contacts (so they close when the relay pulls in on motor start).

[Neal Scanlan]

Hello Steve
I fitted the switch some time back and checked that P1 changed to P2 on the display when I actuated it, which it does. However what I have noticed is that although the display shows the change there is no input/output change and therefore no sound.
I also noticed that the indicator above the volume selector dial stays illuminated with P1.
The only way I can get the change over to work is to power down the 650 and reboot with the dip switch up for projector 2 on the front panel. Using this method all works as it should.

Could you throw any light on to what I am doing wrong.

[Marco Giustini]

I might be incorrect here and I don't have my 650 in front of me but I believe the display shows you the MOTOR running (M1 or M2), the LED above the volume knob shows you the Projector selected (P1 or P2).
You might need both Motor and Projector set to 2.

Screenshot 2026-01-08 225740.png

[Tj Hopland]

The P1/P2 is the optical change over. The M1/M2 is for the SRD if you have that installed and are using it. Optical requires the P1/P2, SRD requires both. The added complexity for SRD is due to the fact that the digital track is offset and run into a buffer so its not as simple as the analog where you just change and play what ever is in front of you.

Note On the P1/P2 controls the 650 gives you 2 ways to control it. Traditionally with previous models no connection was P1 and with the terminal grounded (pin 3 in this case) it was on P2. Here they give the option of momentary pulses so that is why there is also the pin 1 and pin 4. So if for your setup you only want / need one manual switch in one location using the pin 3 option may make sense. Could be pretty much any switch even a light switch. ON would be P2, OFF P1.

If you wanted a switch by each projector you could in theory get '3 way' light switches and wire up two of them but one of the downsides to this would be the switch position being up or down isn't gonna tell you which projector is active, flipping either switch is just going to change the state. Maybe that would work for you, maybe not. For 2 locations it would likely be easier to just use a push button switch by each projector and then the pins 1 and 4. Looking at the switch still won't tell you the state things are in but you would not expect that from a button. The button on or near P1 would do P1 and the button by 2 would be 2. With the 3 way either location could select either projector. The buttons also open up more options like making different levels automation less complex like putting relays on the picture change over so the analog sound just follows the picture.

[Marco Giustini]

more or less as I remembered, thanks Tj.

One question: I believe on the changeover setup I worked on, M1 and M2 were both on all the time? I believe M1M2 was shown on the display. Those were all SRD locations. Do I remember right or was that also a possibility? In other words, was the Motor signal so critical for SRD?

[Neal Scanlan]

Thank you for your help. I’m using a DPDT switch and if I have interpreted your replies I would connect as per the photograph. Am I correct? IMG_0403.jpg

[Marco Giustini]

I think so - though that would result in a SRD drop at changeover as the other projector's motor should start in advance. But if you don't care/don't have SRD, then this should work.

Love the sketch made with a ruler BTW

[Tj Hopland]

I have never tried it the way you drew it. Few areas of concern.....

I have always done the motors as a maintained contact but now that someone is asking I guess I don't know for a fact that that is required. I know for sure it works like that so motor is on contact is close the correct M number is lit on the screen. I guess you could just try it even with the factory jumper wire/plug. We know with the jumper installed its on M1, What happens if you remove it? Does M1 still stay lit? Will it stay till you momentary jump M2? If it does then my guess is then the momentary would work it was just easier to have it maintained.

Second area of concern with the above drawing... The internal logic may not like having M and P directly tied together. Put simply the voltage on each of those pins is looking for ground. When the switch is grounded all is well they are getting grounded as intended and the logic will do what its supposed to do but when they are not grounded the voltage from each if those pins may be kinda wandering around each others pins and logic and confusing things.

It could cause a hard fault where both would just trigger all the time and then the system may ignore any other triggers so won't work. Or worse it could just randomly trigger because of some very slight voltage variation somewhere else in the system or building. Could be really annoying especially if the same chip is maybe also handling the format buttons and can only handle one 'push' at a time.

If the momentary motor thing works and you still wanted this single switch getting a 2 pole switch would solve the issue, M's and P's would have their own contacts. If it has to be a single pole you could likely use diodes to isolate the pins. Something like a 1N4001. Lots of diodes could work its just the 1N400x's was a number I remember being super common. The diodes are basically an electrical check valve. You would stick one of those on each of the 4 lines and orient them so the power could only flow out to ground, they would prevent power from another pin from flowing back up the pin.

I'm not actually sure which way the flow is in this case so you would have to try it and see, it could be power needs to flow in. To figure it out just use the diode as the test jumper wire. Stick the band side on 5 and then hit 4 and see if it goes to P2 (assuming it was on P1) if it doesn't go flip the band away from pin 5. One way won't do anything and the other way should work. Which ever way works have the band then pointed that way.

Back in the olden days you could just pop over to the Radio Shack across the street downtown or across the food court in the mall and pick up a 5 pack for $1. Times have changed. I guess now days everyone has a bunch of junk electronics around so as long as you can work with little short nubs of leads you could just take random stuff off junk boards. For this application there are proabbly 100's if not 1000's of models of diodes that would do the job. Just has to be something old enough that its not all chips.

[Tony Bandiera Jr]

Thank you for your help. I’m using a DPDT switch and if I have interpreted your replies I would connect as per the photograph. Am I correct? IMG_0403.jpg

Nope. As TJ mentioned, the internal logic circuits cannot have the motor and changeover tied together like that. You MUST keep them isolated, and the motor signal is a SUSTAINED one, and must be held as long as the motor is running. The changeovers are also sustained but are independent of motor status. (Your hookup would initiate the changeover to the incoming machine as soon as you start the motor, and would also be HOLDING the outgoing projector until it's motor was shut off.)

Just do as Steve said, get relays with the appropriate coil voltages for your motor start signals. (Make sure you read his correction in his second post.)

As for the changeovers, a dual-coil "latching" relay (with the coil voltages matched to your changeovers) will take care of the changeover signals. Use ONLY pin 3 for the changeover, and connect whichever set of contacts on the latching relay is closed when you open P2's changeover. OR, a method I used for a long time (and cheaper than a latching relay) use a microswitch with a long lever on it, mounted to the P2 changeover dowser, so that the switch is pressed when the dowser is open. Cheap, simple and easy to maintain.

Later all of my work was using AMX control hardware and my program code would fire appropriate relays fro the motor start and changeovers. I still have a good amount of lageacy AMX hardware and all the programs to build a control system for you if you want one.

[Tj Hopland]

I just noticed in Tony's quoted version of the diagram that he did say DPDT switch, The way it was drawn it looks like a SPDT, but if it is indeed a DPDT then the M's and P's can be separate so the only question will be is the momentary M's Ok. I have not had a chance to look for a manual and see if it does state that the M's have to be maintained. Initially I was gonna say they have to be but all I can say for sure is that how I always did it so I may just be assuming thats the only option.

Next week I will be actually hooking one of these up but in my case it would be a lot more work to make the M's momentary so they will be maintained and I know that works so for me at least if momentary works is more of a curiosity that won't likely ever come up again.

[Neal Scanlan]

Thank you for all of your help. Perhaps it is worth describing my setup.

I have two projectors. Both projectors utilise the same platter, and I play an entire film using one projector. The choice of which projector to use for each showing is based purely on the enjoyment of using one or the other.

The goal is to have a changeover switch (or switches) that place the 650 in either P1 or P2 mode, essentially for sound only. I think I may be misunderstanding the distinction between switching the motors and switching the inputs from the sound readers, hence my current solution of rebooting the 650 after moving the DIP switch on the front panel to select sound from P1 or P2.

If I were to switch between pins 2 & 5 to 4 & 5, do you think this would give me the correct outcome?

[Marco Giustini]

I suspected it wasn't a real changeover. I feel that if you just have the relevant Motor contact on all the time and the relevant P contact tied to your dowser, it would do what you want. Alternatively, have the relevant M and P contacts to a switch, just bear in mind the CP650 will play analogue sound as soon as the correct (P)rojector is selected.

In a cinema I used to work - platters, single projector - the CP650 was hardwired to P1M1. The reason was that if the dowser failed to operate, I could still open it manually and I would still have sound and continue the show. The downside was that if I had to start a show from in the middle of something, the CP would play the "meowing" sound while the projector was getting to speed. (I'd usually manually change from a NS format to SR or SRD to avoid that).

Now I'm thinking about, I believe in your situation you can have your Motor contacts - both M1 and M2 - set to ground all the time. The CP will show M1M2 and happy days. SRD would work and SR would follow the P contacts.