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Author Topic: No Left Surround CP55 Michael Wilkinson The Entertainment King of Colusa and Beyond Posts: 89 From: Colusa, CA USA Registered: Apr 2004 posted 07-06-2008 03:35 PM                        I'm working on a CP-55 that does not have output from the left surround (S) terminal on TB3. A Cat 441 is installed and the right surround is working fine. The backplane mods seem to have been done poorly-but correctly. The signal present indicator is functional on the Cat 242 and there is signal at the test point. Beyond the cat 441 this processor is original. No mods have been made to the cat 243 either. Any help would be great!  |  IP: Logged Christos Mitsakis Expert Film Handler Posts: 242 From: Ag.Paraskevi, ATHENS, GREECE Registered: Sep 1999 posted 07-07-2008 03:26 AM                     Michael, Is the problem on digital playback or both digital and analog? If in analog, is there any cat242 available to swap and see if problem stays? Did you check the corresponding amp channel for failure? Christos.  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 07-07-2008 03:47 AM                     If the backplane mod was done poorly yet correctly, I bet there are tons of cold solder points done at these points. I'd redo all of the solder connections for cold soldering causes resistance factors.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 07-07-2008 06:48 AM                        Old memories: Is the jumper on the terminal strip? Louis  |  IP: Logged Michael Wilkinson The Entertainment King of Colusa and Beyond Posts: 89 From: Colusa, CA USA Registered: Apr 2004 posted 07-07-2008 04:19 PM                        Christos, the output problem occurs in analog and digital and the amps are working fine. I don't have ready access to another CP-55. For the time being I have switched the DTS surround output to MONO and am using the rs channel input-output terminals for both left and right surround amps. I did this several months ago with the assumption that a new cinema processor would be on the way but here we are; I have been told that the problem has existed for quite some time-perhaps going back to the original cat 441 install. Monte-I have repaired a couple cold solder joints that came off as I was poking around. I will re-solder the others. The other thing I noticed is that the resistor is 100K-5%-not 105K...could this cause a problem? Also if it is that sensitive there are a couple of other traces that were nicked near the cut trace (out of control utility knife most likely). Although they check out as still being conductive maybe I'll jumper those too. The thing that confuses me is that I can get left surround signal at the "S" test point on the cat 242 card. Louis-I had added the jumper between TB3 2-4 but that jumper is to benefit the RS....thanks for thinking of it I assume that the card edge connectors are lettered A-T excluding I & O?  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 07-07-2008 07:02 PM                     quote: Michael Wilkinson For the time being I have switched the DTS surround output to MONO Aha, a dts6. I've had this exact problem happen on a couple of these. It wasn't the Dolby processor at all, but the dts. Put it back to stereo surrounds and flip the wires going into your CP55 and see if the other surround channel suddenly doesn't work. Now for the best news...if that is indeed your problem, I can't remember what the fix was. I'm such a help.  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 07-07-2008 07:40 PM                     (yea, quite the irritating factor to find out when you think of it being a processor problem when you lift up the lid and find the 3 DIP switches set to <mono> instead of <split> surrounds on a DTS-6 unit)  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 07-07-2008 07:58 PM                     Since he has the signal at the Cat 441 test point...the signal is getting to the card. Since it is the left surround, a quick and dirty test (on optical) is to PULL the card...if that restores the signal, then it is the Cat 441...it is a little known secret that on a CP65 or CP55...the Cat 241/441 are not needed to pass the surround signal! The cards will merely apply an EQ for the surround and, of couse, bass enhancement. The signal path was designed to allow the signal to flow without the card (only for the Left Surround though...as it was a design introduced for the CP-55. Okay...so moving on...does the Cat 242 light its "S" LED? If so, it made it there but is failing in its output stage. Note, there is a High/Low jumper (white wire) for each channel, verify that it is in the "High" position (installed). It will be labeled "W8" and it may have a blue jacket instead of white. Next on the hit parade are the dreaded, often cursed "Bypass Relays" on the back. If you have WHITE colored relays with the largish BLACK lettering of "STC"...RUN!!! Or at least change them to good relays. Those are a known problem and are called out in a Dolby Field Bulletin (I don't know which one off hand). The relays are "DIP" style with 24VDC coils in a 2-C configuration. Suitable replacements include Omron G5V-2-DC24 and I'm sure there are others. If you have another CP55 in the complex and can experiment while they are not on screen. Try swapping the Cat 242 (don't be worried about level... you just want to know where the sound is failing). If the problem moves with the card, you've found it. As for the 100K versus 105K resistor...that only affects the PN level for the subwoofer. With the Cat 241, the subwoofer was derived from Lt and Rt...with the Cat 441, the subwoofer is fed, post decoding from L, C and R. The 105K resistor gets the level correct for the new configuration. The person that did this has you off by 5%. While 105 resistors are available they are not often sitting around at the Radio Shack down the street. However, both 100K and 5.1K are pretty standard...there would have been no harm is wiring the resistors in series. This would have you in less than 1/10% off. 4.7Ks are also pretty available (and more so) and would have gotten you closer....lazy tech. Steve  |  IP: Logged Michael Wilkinson The Entertainment King of Colusa and Beyond Posts: 89 From: Colusa, CA USA Registered: Apr 2004 posted 07-08-2008 01:29 AM                        Gee thanks Brad! But seriously the problem appears to be an output stage problem that occurs both in Digital and analog!...OH WAIT-HOW SHALLOW OF ME...but I don't see how it could be the DTS given signal from both surrounds making it all of the way to the cat 441(rs) and cat 242(ls)...please explain if you remember! quote: Steve Guttag Since he has the signal at the Cat 441 test point...the signal is getting to the card. Since it is the left surround, a quick and dirty test (on optical) is to PULL the card...if that restores the signal, then it is the Cat 441...it is a little known secret that on a CP65 or CP55...the Cat 241/441 are not needed to pass the surround signal! The cards will merely apply an EQ for the surround and, of couse, bass enhancement. The signal path was designed to allow the signal to flow without the card (only for the Left Surround though...as it was a design introduced for the CP-55. Steve, the signal present indicator for the LS is on the cat 242 and the RS is on the cat 441. Doesn't the LS signal pass through the cat 241/441 before it heads to the signal present & test points on the cat 242? This being so it would rule out my cat 441 as the culprit? When the unit is in either analog or DTS (Split surround mode) I have the signal present indicators and audio at the respective test points!!! The relays are the STC type...so this is sounding like it could be the problem??? Probably especially likely since this unit looks like it went end over end down a flight of stairs...The fact that it's working at all is a testament to good engineering! I need to send in a picture of this thing!  |  IP: Logged Christos Mitsakis Expert Film Handler Posts: 242 From: Ag.Paraskevi, ATHENS, GREECE Registered: Sep 1999 posted 07-08-2008 02:53 AM                     Steve seems to be closer to the solution (as always). As for the resistor, since it's hard to find a 105K resistor (even at specialised electronic stores here in Athens), I've done several modifications using a combination of 100K and 5.1K which are radily available, with the knowledge that you have a tiny bit lower level at setting the SW. I've seen mods also with no resistor used at all. C.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 07-08-2008 07:02 AM                     Since you have the LED glowing on the Cat 242...you are down to the output stage of the Cat 242 (unlikley, though possible) and the crappy relays. Since the "STC" brand of those WHITE relays are a know source of audio drop outs...CHANGE EM...odds are, life will be harmoneous again...or at least better balanced in the surrounds. The quick verification is to swap K3 with another one of the 3 relays just to verfy you have solved the problem. Either way though CHANGE THOSE RELAYS...if they aren't your problem now...they will be at sometime. If they are not the problem though, you either need to RX the Cat 242 or have a bad solder joint on the Cat 242 edge connector ("S" output). It is unlikely at this point, but it is worth a look. Steve  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 07-08-2008 09:04 AM                     But Mike, I was only trying to help by skimming through your post and missing all of the pertinent information.  |  IP: Logged Michael Wilkinson The Entertainment King of Colusa and Beyond Posts: 89 From: Colusa, CA USA Registered: Apr 2004 posted 07-09-2008 12:11 AM                        Thanks Steve! I'm not getting another chance to work on this little gem until Friday AM so I'll let you know!!! I'm lucky enough to have "Electronics Plus" on my commute path! They have everything-no cheese though. http://www.electronicplus.com/ and Brad, It seems that you were pretty quick to point the finger at DTS! What did they ever do to you; did the founder of the company drop you on your head when you were a baby?  |  IP: Logged Michael Wilkinson The Entertainment King of Colusa and Beyond Posts: 89 From: Colusa, CA USA Registered: Apr 2004 posted 07-15-2008 06:43 PM                        Thanks Guys!!! "STC" was the name of the problem...I went to the electronics store and for just over $20 I have three new relays!  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 07-24-2008 08:17 AM                     I found the Dolby Field bulletin on this (finally)...It is FB #161...Intermittent audio on CP55 when power is switched on. Look for it to hit the manuals section...some day. Steve  |  IP: Logged

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