Film-Tech Forum ARCHIVE: Benchtesting CP50 and CP65

This is topic Benchtesting CP50 and CP65 in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Luciano Brigite (Member # 1104) on 06-03-2007, 01:22 AM:

Hello ,

I received a few CP50 and CP65 as part of a deal and I'd like to know if there is a way to bechtest htem, without having to hook it up to a sound reader and do all hte set up for it.
Basically what I want to do is checking them to see what's working and what isn't,reset preamps,equalizer input/output levels and so on.. make sure the CAT150 are working ok and calibrate the CAT64's input/outputs (often found mis-set here) before sending them out .I don't have a working projector at the moment (mine are dismantled ,parts lying all over the place in boxes and cans waiting for free time to work on them)to run test films then an external device to generate a signal is needed.. but I don't know what signal and level to use for hte test, need some input on it too.
Thank you

Posted by Louis Bornwasser (Member # 3063) on 06-03-2007, 07:46 AM:

The B chain is simple; just generate the tone or pink noise and measure it on a scope.

The A chain wants to see a signal about equal to a microphone; so -55 or -60 db should do it. You could use the output of another CP to generate what you need and pad it down appropriately. Louis

Posted by Kenneth Wuepper (Member # 1174) on 06-03-2007, 11:56 AM:

If you have the sound head for your projector with the motor in running order, you could make a small accululator for 10 or 15 feet of audio test film and feed the scanner output signal into the various processors you are testing.

The advantage to this system is your ability to have a known source for comparing all of the processor units tested. The signal could be from various changeable loops of test film, Pink noise and Dolby Tone. The picture portion of the machine is not required for your testing purposes.

KEN

Posted by Michael Schaffer (Member # 1204) on 06-03-2007, 12:22 PM:

But Ken, Luciano siad he did NOT have a working projector or even just sound head available right now. That was the whole point of the post.

As Louis said, testing the B chain related components is easy, and the A cain components can be tested by feeding them a tone from a generator, too. I have never done that, but I believe a level of about 120mV should be appropriate for the projector inputs. However, that needs to be confirmed by somone who has actually done that "on the bench".

But - Luciano, you can not set up the A chain on the bench and then just send the units out for plug and play. Each individual projector and processor combination needs to be aligned. That is the whole point of the A chain alignment process. You do not know how well a projector is aligned until you hook it up to the processor and play the test loops. Even if you know that the projector is well aligned as far as left-right, illumination uniformity, focus and azimuth are concerned, you still need to calibrate the level within the actual setup.

Posted by Steve Guttag (Member # 268) on 06-03-2007, 02:43 PM:

120mV at the projector inputs is WAY too high...however here is a little trick that will work with ANY Dolby preamp (and probably most others)...

For each channel use two 47K resistors...one each on the positive and negative terminals (4 resistors total for both channels)...

You can then connect any normal line level source to the inputs via the resistors (the resistors are used in SERIES with your signal source)...you can use a signal generator, CD player...whatever you have.

Posted by Michael Schaffer (Member # 1204) on 06-03-2007, 03:32 PM:

What's the correct voltage coming out of the preamp when the Dolby level is set? It's not 300mV, but I can't remember exactly what it typically is. Apparently not 120mV.

Posted by Luciano Brigite (Member # 1104) on 06-03-2007, 04:18 PM:

Hello again,

Atr hte moment, I don't have anything I can run a film loop working,both of my projectors are in pieces.
I know the A-chain can't be done nor anything else but that's not the intention at this moment.
I just want to test and make sure the processors are in working order and verify the internal level setups ( mostly hte CAT64 inputs/outputs levels, since htose are often messed up by others in the theatres around here resulting in saturated output cards,distorted signals or then low levels in the auditorium and high noise. Also want to make sure the CAT150 is working right. (fortunately one of the CP50 and the 65 has the CAT150E,only the ohter CP50 has a lower version,dual card CAT150D if I'm not wrong)
Is there any use for the dolby tone generators built in the NR modules? ( liking the test points on the meter cards in the CP50 activates it) would it be suitable to set the equalizers in/out levels?
Been a while since I had to deal with those old processors that I forgot most of the procedures for them [Frown]

Luciano

Posted by Ben Wales (Member # 92) on 06-03-2007, 05:03 PM:

All the Internal Dolby Tone was a Signal Level, ideal to check you get signal path through the CP50.

You will need a Cat85 (Pink Noise) Gen card to set the EQ, make sure all the Cat64 (input) are set to min and adjust the output to 150mv, also the 27 1/3octave pots are set flat, ie 12oclock position.

I would make sure the output card gain is turn down, say 5 turns on each channel as a starter, before all that I would check the Solder joins on the Back Plane of the CP50 as that tends to be a issue with dry joins.

Posted by Sam D. Chavez (Member # 1841) on 06-03-2007, 07:57 PM:

The 2 Dolby tone signals from the CP50 will not stay in phase with each other so are not much use except to tell you the Cat. No. 150 is steering the audio signals randomly all over the place; kind of like a car with no steering wheel.

Posted by Michael Schaffer (Member # 1204) on 06-03-2007, 08:21 PM:

Sam - why? Please explain further!

What's the input range of voltages that can be accepted coming from the solar cell preamp and accomodated by the level range on the processor's preamp card, and what is the voltage of the signal coming out of the preamp card?

Posted by Steve Guttag (Member # 268) on 06-03-2007, 09:16 PM:

The output of all Dolby optical preamps from the CP50 onward (I'm not sure about the CP100 nor the digital units since it may be in the digital domain at that point) are at 300mV.

You CAN use the Dolby Tone of the Cat 22s to set up the Cat 64 output trims IF you only use one Cat 22 (say left channel) and then switch each EQ card into the Left position and set your 150mV level (referenced on the Cat 111, 117 or Cat 517). As others have mentioned...since Dolby Tone resides in the 800Hz region (and is modulated)...one should have at least 630, 800 and 1K pots centered before setting the output trim.

Steve

Posted by Richard May (Member # 2627) on 06-03-2007, 09:49 PM:

Lonnie had told me a better and more accurate way to set the Cat 64 card outputs with the pink noise gen., but I forget exactly how. Maybe Sam knows.

Posted by Michael Schaffer (Member # 1204) on 06-03-2007, 10:04 PM:

quote: Steve Guttag
The output of all Dolby optical preamps from the CP50 onward (I'm not sure about the CP100 nor the digital units since it may be in the digital domain at that point) are at 300mV.

Here is where I am getting confused a little bit, because in many cases when I measured the output from the analog preamp card after setting Dolby level, I found the level more around 233mV. Or was it 266mV? I can't remember now. In any case, markedly lower than 300mV, a greater deviation than can be explained by the known variance in some color stock test loops.

Posted by Steve Guttag (Member # 268) on 06-03-2007, 10:05 PM:

Yes, in the day, I used the PN card since then you don't need to fool with worrying about where the individual frequency bands are set. However you really need an analog meter with you to do it right. The level one set escapes me at the moment...it has been a LONG time since I've needed to reset a Cat 64a.

Posted by Luciano Brigite (Member # 1104) on 06-03-2007, 10:47 PM:

Hello again,

Steve, thanks for the information regarding the pre-amps output levels and the tip regarding the use of internal Dolby tone generator to reset the CAT64.
I could only start the works in one of hte CP50 and already got a busted CAT150, it doesn't surprize me it's the older,dual card version. it's surround channel is popping and hissing almost constantly, with or without signal, it's the last of the dual card CAT150, I believe, since it has the signal leds in it.
Also found a few damaged trimpots in one pre-amp card and thoseold,grey,can-type capacitors in the PSU with the usual brow stuff leaked out and dried.a little bit of fun for hte next day's nights.
and yes, I have those analog audio AC meters and signal generator
Going to use the meter soon on them [Big Grin]

And I did notice hte effect Sam mentioned in his post, having the two NR cards in with the signal activated,the center chanel puts out a weird ( to ears) signal and the surrond comes and goes at random. While I'm doing the testing, I'm using a small bech amplifier. will save hte big one for the final testing,so I can really annoy the neightboors [Wink]

Thanks again!

Posted by Christos Mitsakis (Member # 143) on 06-04-2007, 05:05 AM:

What Sam said from another topic (http://www.film-tech.com/ubb/ultimatebb.php?ubb=get_topic;f=1;t=001326#000000):

"The best way according to me is to set the input trims all the way off and set each output trim to about 200 mVolts (measured at the input to the VCA card) of pink from a Cat. 85 After setting house EQ, and before setting final sound pressure levels.

The method described in various versions of the CP50 manual rely on using test film and this in turn is thrown off by the state of the A chain including SR cards. Setting it from a generator goes around all this."

Since we're discussing CP50 territory: Where is PN injected in a Cat560 to Eq the surround channel and set auditorium level? The SW input is also way in the card than its predecessor (160) making things difficult. Should I use backplane pin A1 for the SW and pin A5 for the surround?

Christos.

Posted by Luciano Brigite (Member # 1104) on 06-08-2007, 12:07 AM:

Hello all,

Thanks for the information until now on how to test these 2 CPs.
I have another question about the CP65 now.
The one I have here and I'm testing right now makes a "pop" in hte sound everytime it's switched from Dolby A to Dolby SR or the opposite. each time it's switched, hte leds on hte CATs 222,150,441 and 242 blinks ( all channels) it happens with signal present or not.
Now the processor is doing the same kind of popping while working and this time all the leds mentioned before blinks and the two green leds on hte cat.240A. is it indicating a problem with hte pre-amp card? I also noticed that htese "pops" sometimes follows hte signal being reproduced ( like a hand's clapping,shot,slamming door and the like.) also happens,but not always when a sudden increase of level happens ( like when a loud passage happens all of sudden in hte movie)
In case the pre-amp card is at a fault, where I can look for one and have it here in a few days? or what should be replaced on it to solve the popping? is there any schematic of it available?

thanks!

I forgot to mention one thing: this CP65 is missing the spare pre-amp card. [Embarrassed]

[ 06-08-2007, 11:59 PM: Message edited by: Luciano Brigite ]