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This topic comprises 2 pages: 1 2
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Author
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Topic: CP500 Output Distortion and Panel Meter Glitches
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Tom Ostertag
Film Handler
Posts: 41
From: St. Louis, MO, USA
Registered: Jun 2014
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posted 09-03-2016 10:28 PM
Hi all,
My CP500 has developed an odd intermittent problem. Occasionally one channel of audio output will sound distorted after power-up. This sounds like it's happening in the digital domain, almost as if it's missing one or more bits of precision, very similar to a "bit crusher" effect. The issue is present with any input selected. The first time I heard the issue it was in my front left channel, and most recently it happened in the right surround. In both cases, power-cycling the processor solves the problem.
To make matters worse, when I power-cycled the processor after the last occurrence of this issue, my front panel meters started showing periodic high level spikes on the Rs and SW channels (even with a silent source), while the outputs sounded fine with no clicks/pops/distortion. While passing audio, the meters also started frequently freezing for several seconds at a time before updating again. This processor has always had some sort of "phantom level" on the SW meter since I acquired it, but this is much worse.
I'd have to verify, but I think I'm on the latest software revision. Also, the clock stability modification has already been performed from the factory.
Has anyone else noticed instability in these areas? Should I start looking at capacitors, or any specific boards? Component-level troubleshooting and repairs are not foreign to me, but any ideas on where to start would be much appreciated!
—Tom
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Tom Ostertag
Film Handler
Posts: 41
From: St. Louis, MO, USA
Registered: Jun 2014
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posted 09-06-2016 12:50 AM
Thanks for the info so far.
I've had this processor for probably a little less than a year. I got it off eBay, so its history is unknown. I've added the Cat 885 6-channel ADC and 683 crossover cards to suit my application in my home screening room, and also replaced the 5V 1F "super capacitor" on the Cat 984, which was physically leaking a bit. Apart from that, the components and PCBs look pristine.
There has always been some noise in the VU meter for the SW channel, with the meter randomly rising and falling without any signal I/O. I mentioned that to one of my friends, and he didn't seem at all surprised, so I figured it was a common and harmless issue. Since it got worse around the last occurence of audible distortion, I thought there might be some correlation. I've been a victim of troubleshooting coincidence enough times to know better though, so I realize they may not be related.
Since I've had the processor, and I use it a few times a week at least, I've heard audible distortion as I described only twice. Probably a couple few apart, with the most recent one being last Tuesday. In both cases, a power cycle eliminated the symptoms.
Signal flow would suggest the source of the distortion is either the Cat 675A DSP that's used for equalization, or the 684 that's telling it what to be and do. Of course the components look flawless, but I haven't tested any electrolytic capacitors yet. This may just be one of those little issues that has no reasonable explanation.
I work in broadcast television, and we have broadcast-quality HD video monitors that occasionally crash and have to be rebooted. Monitors! The days of digital device problems surprising me are long gone.
Well after all that, I just powered up my CP500 to check the software version, and I'm on 1.61. I thought for sure I was on 1.65. That's a real glaring issue right there!
More to follow when I get the thing updated, hopefully later this week.
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Tom Ostertag
Film Handler
Posts: 41
From: St. Louis, MO, USA
Registered: Jun 2014
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posted 09-07-2016 01:53 AM
quote: Scott Norwood What format is selected when you have this problem? We had a similar issue in a 6-plex, but only in SRD. Switching to an optical format (and leaving it there) or rebooting fixed it.
When it does happen, it's on that output/speaker channel, no matter what the input is. You can switch around between external 6-channel, nonsync, SR, etc, and it's there. I don't have a Dolby Digital penthouse yet, so I don't know about SRD. Interesting that you had distortion somewhere else, and reboots fixed it.
Well, I finished the upgrade to 1.65 tonight. Super easy with Load500 v2. The hardest part was lugging the XP desktop with the real serial ports upstairs!
So far so good! I rebooted the CP500 a couple times, and haven't seen bad meter readings yet. No distortion yet either. Only time will tell if that was all it needed!
I was skimming through my last post, and realized I called the Cat 685 an 885, and the 684 a 984. That's what I get for late-night typing. Oh well, I'm sure y'all knew what I meant.
I'll be doing some more screenings soon, so I'll keep an eye and ear on things closely and report my findings!
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Tom Ostertag
Film Handler
Posts: 41
From: St. Louis, MO, USA
Registered: Jun 2014
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posted 09-08-2016 12:32 AM
quote: if someone reports of distorted sound which fixes itself with a reboot, it's most likely the 500 itself!
Agreed! I've most certainly narrowed it down to the processor. I have some audio distribution amps in another frame, and a patch panel, but the reboots and my booth monitor rule out those things. The distortion was verified to be present immediately after the CP500, and not before. And the CP500 was the only device I rebooted to clear the issue. Well, the amps were powered down too for safety, but the booth monitor shows the distortion before the amps.
quote: Louis Bornwasser Don't forget the small jumper wire from case ground to low side of an output. Kinda not in all manuals.
Indeed, the chassis–signal ground jumper is in place on the CP500, and the CP500 is used as the central ground for all line-level devices. Not a ground loop in sight!
I ran a movie through it tonight (via external 6-channel in this case), and I didn't have any audio issues. Also tried some non-sync sources with the same result. However, the phantom meter levels came back, so that looks like a minor annoyance I'll be stuck with. I expected that, after all the reports of that being normal for others. As long as it's nothing in the audio! More monitoring to come.
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