This is topic Strange CP-55 problem in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Mark Gulbrandsen (Member # 72) on 05-02-2001, 08:46 PM:
Although I have yet to really delve into this strange problem I have made some preliminary checks which turned up nothing so I thought I would post this odd problem here and see what turns up.....On an older CP-55 with CAT 222 noise reduction I get no red LED on either of the 222 level set readouts. Between shows today I swapped a number of spare cards to see if it was as simple thing..alas it is not. What happens is that when you power up the unit, the 222 level set LED's do their normal thing and when the red LED comes on it gradually fades out to nothing. All voltages SEEM? to be present at the backplane but I am not 100% sure as I don't have schematics with me and unfortunatelly there are none here in the manuals section for me to be sure from. Has anyone run into this? And does anyone know the actual pinout for the 222 card? I have a strange suspicion that this is a backplane problem but I have plenty of time tommrrow to sort this all out. Any input would be appreciated since I am in the field and away from my manuals, etc.
Thanks!
Mark @ GTS
Posted by Randy Stankey (Member # 64) on 05-02-2001, 09:39 PM:
I had one situation where I thought it was a bad card in the processor and I worked for an hour to debug it to no avail.I finally took a look at the sound head and found that it was all out of whack. Somebody had knocked the solar cell out of line. It was only partly reading the tracks.
I was P.O.'ed at myself for not looking there first.
Posted by Mark Gulbrandsen (Member # 72) on 05-02-2001, 11:22 PM:
Hi Randy,
That same thing has happened to me too. In this case I did have time to run a loop of tone. The Green LED's indicate about normal brightness for tone but I still have to check the level with a scope to be sure. Infact I took both the preamp and cat 222 and stuck them into another 55 and they work fine. But the 222 does not function correctly in this particuluar chassis for some reason or other. Normally both lower scale red LED's should be lit up on the 222 but they are not when plugged into this chassis.
Mark @GTS
Posted by Darryl Spicer (Member # 711) on 05-03-2001, 12:46 AM:
Mark,What does the sound sound like when playing a feature film in the auditorium. Does it sound like you are getting all the high frequency levels in the sound. When you listen closely does the high frequencies stay constent or do they sound like they are going in and out? If the first question is no then you need to hook up the RTA and scope to the test points and check the A chain. If the answer two the second question is yes then you need to swap a noise reduction card from another unit and see if the problem persists. If it does then it is probably like you said a problem on the motherboard. if it doesn't then order a new noise reduction card. If there are no noticable problems in sound then I wouldn't worry about it.
Posted by Gordon McLeod (Member # 33) on 05-03-2001, 09:54 AM:
Since it isn't the Achain nor likely the cat 222 since it will work in another unit check the Cat150 by swapping it it maybe having some DC offset problems
Also the older preamps with the transformer block in the centre did some wierd things
On possiblity is to unplug the preamp and conect a oscilator to the preamp out terminals on the backplane and test the NRM that way
Posted by Steve Guttag (Member # 268) on 05-03-2001, 05:20 PM:
Mark,I'll check my old schematics and see if I can locate the original 222 (not the 222A, as is used in the CP-65).
You have definately hit the nail somewhat since you are correct, on the 222 the bottom red LEDs are always on when the signal is below Dolby level (ie no signal).
Talk to you later.
Steve
------------------
"Old projectionists never die, they just changeover!"
Posted by Mark Gulbrandsen (Member # 72) on 05-03-2001, 06:08 PM:
Here is what happened this morning. I swapped the 222 form another unit and low and behold it went up in flames! The manager happened in and mentioned that this CP-55 had killed another 222 at one time a while back. The 222 that was in the 55 is now in the theater whose card went up in flames working fine. I talked to Norm at Dolby about this as well and it kind of has them stumped too. He thinks that either the backplane or the bypass relays are bad. I ordered both for tommrrow so we'll see.
Darryl,
I have clean 300mv of tone at the preamp test points with little to no offset at the preamp output. The front end is fine on this one. There is a small amount of tone that will bleed through with the volume cranked all the way up but not enough. I'd bet that if I jumpered the LT, RT lines past the 222 slot that I would have full audio. The problem is that it needs to be 500mv and I am not sure that the preamp can do it. They're running fine on DTS anyway for now.
Mark @ GTS
Posted by Randy Stankey (Member # 64) on 05-04-2001, 12:15 AM:
YIKES!!I just had a CP-55 that smoked an EQ card. A replacement is on order, but after hearing this I think I'll take a closer look at the processor before I go sticking the new card in. 
Posted by Mark Gulbrandsen (Member # 72) on 05-05-2001, 06:26 PM:
I found the problem today. I took the entire unit apart again. I examined the backplane very carefully with a bright light and found a piece of crud wedged in between the inside of the backplane and the socket for the NR unit. By what happened to the last nr card I'd guess it was a metal piece of some sort that has been in there for a long time. This unit had eaten another NR card a number of years back. I dislodged the crud and now its working fine. It resembled the stuff you get when you make an electrical knockout hole using a drill.
Mark @ GTS
Posted by Jon Bartow (Member # 241) on 05-05-2001, 07:33 PM:
During an installation very few electricians will bother to cover equipment or fully clean up after themselves. Therefore little bits of metal (that conduct electricity very well, and are sometimes magnetic) get strewn all over the place. We "field engineers" are doomed to be finding the little buggers in strange places for years to come. A few weeks ago at one of my theaters I had a piece of metal that became lodged between the coil and flapper in a relay. Prevented the automation from cycling properly. Four hours of driving to remove an 1/8" piece of metal. *sigh*