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This topic comprises 2 pages: 1 2
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Topic: QSC DCP processors coax (S/PDIF) input reversed
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Leo Enticknap
Film God
Posts: 7474
From: Loma Linda, CA
Registered: Jul 2000
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posted 11-10-2018 01:30 PM
I installed a DCP300 a few months ago, but did not hook up any alternative content (this wasn't part of the job as specified by the customer).
It could have been a manufacturing or QC glitch in that one specific unit, rather than a design issue: someone just got confused at the end of a long shift, and soldered the wrong wire to the wrong pin. If anyone else has access to a unit, it would be interesting to look at it and see if these poles are reversed. If they are, it would suggest, as you suspect, that they got crossed on the schematic, CAD file, or whatever document was used to inform the manufacturing process. If they're not, it would suggest that there is a bug in your unit that, for whatever reason, wasn't caught in QC.
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Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 11-10-2018 06:50 PM
It wasn't so much a "catch" as "Why doesn't this damn thing work reliably, it does elsewhere!" In truth, my boss, Neal caught it and rewired a coax, in the field, to reverse the polarity!!!
Any of our other sites using this processor, I'll put a polarity switcher via a male/female connector with the wires crossed so it will be plug-n-play.
As someone that did design hardware (PCBs), I'm sure Harold is correct. It is pretty easy to do. You define a schematic symbol for a piece and in that symbol you define pin 1 on up (I generally always made pin-1 square for THD) to also aid in it). Then you define the actual component that will be on the PCB and again, you define the pins and that is when the two get matched up.
Another one that can get you is mirror (x or y flips). This is particularly true with Dsubs where they look the same in correct or mirror orientation (just the gender changes) but if you aren't careful, you could get a male connector wired female (or vice-versa).
The layout person has the added reality that they will work on both sides (of each layer, in a multi-layer board) so seeing something flipped isn't necessarily uncommon, yet correct, including writing where you want the bottom layer to "read" correctly.
I am in no way trying to embarrass anyone here. It is strictly for information for those that might have problems in the field. As some have pointed out...how long did it take for this to show up? I think it is dumb luck because I'm sure most don't have anything connected to it and those that do have something that is typically not grounded so it wouldn't show itself.
I ran into a similar thing on a Panastereo piece (CM230EX monitor) where pin 1 on an RS232 connector was referenced instead of Pin-5 (one of those simple x-flip mistakes). If you were in the same rack as the unit, you'd likely not notice because everything is probably using the same ground reference. But if the thing controlling is isn't or is totally floating, then there is no return path for the RS232 and it wouldn't work. A simple mistake with a simple fix but easy to get through QC.
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Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 11-11-2018 07:41 AM
I think the bulk of the systems that use the coax input (no optical on the DCP series) are for Blu-ray players that lack analog outputs (a very high percentage now). Providing that those players are ungrounded (as most consumer equipment is with just 2-prong AC inputs) and possibly using transformer coupled outputs (possible though less likely since transformers cost money and consumer gear often is value engineered), people haven't hit upon it.
The fix is simple enough, in terms of making a polarity flipping adapter. I'd say the harder question for QSC is what to do for new units. Are you really going to "Rev" the fiberglass on a mature product like the DCP where the percentage of complaints is miniscule (with respect to the Coax input, at least). Do you spend the time/money on a modification to all new units for again the off chance of the right circumstances that show the problem? Or do you document it and, if the customer requests, provide an adapter that corrects the problem on an as-needed basis? I think this option is what will be chosen. Again, I have zero knowledge of this, it is just my guess.
I think people will start migrating to the DPM line of processors and QSYS like of DSP processors rather than continue with the DCP line, not because of this problem but because the newer processors will better fit their needs and cost-effectiveness. The DCP line is now a bit mature and based on really their last generation of equipment, like Basis (it is only Cobranet capable, not Dante or AES67) and Cobranet has fast fallen by the wayside...unfortunately, since Cobranet is about as rock solid as network audio gets. But it is VERY mature now.
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Leo Enticknap
Film God
Posts: 7474
From: Loma Linda, CA
Registered: Jul 2000
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posted 11-11-2018 10:50 AM
quote: Steve Guttag
I think the bulk of the systems that use the coax input (no optical on the DCP series) are for Blu-ray players that lack analog outputs (a very high percentage now).
Why wouldn't you use the HDMI in that situation? You can take eight channels of PCM that way, whereas S/PDIF or TOSlink gives you the bandwidth for two of uncompressed, only allowing more if you take the audio out of the player using a compressed codec (e.g. AC3 or DTS), and decode it in the processor.
The only situation in which I'd use S/PDIF or TOSlink for BD audio is if the player didn't have 7.1 analog out, and/or the processor could not accept HDMI audio in. The DPM300 falls into that category (and furthermore lacks an optical input, according to the specs page), as does the CP750, so you're probably right in that some users could want the S/PDIF input for a DVD/BD player.
But if it were me, I'd try to dissuade someone from making that choice of processor if they wanted to use it in an installation that was going to play DVDs or BDs more than once in a blue moon. I don't know if the DCP line can decode AC3 or DTS, but if it can't, then if you choose this processor, either you're stuck with L/R stereo, or you'd have to use an external HDMI to AES converter, and use AES channels 9 through 16 for the input.
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Leo Enticknap
Film God
Posts: 7474
From: Loma Linda, CA
Registered: Jul 2000
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posted 11-11-2018 04:45 PM
quote: Steve Guttag
As for getting it into the IMS...no, it isn't just a single button for them, unless it is the Barco ICMP.
With an external automation system in use (either one specifically designed for movie theaters such as, dare I say it, ours, or one for a/v installations and high end home theaters such as Crestron, AMX or Q-Sys), the two or three switching operations involved in routing HDMI through an IMB can be combined into a one-cue or one-press as far as the end user is concerned. That is how the vast majority of our installations do it.
I'm not arguing with you that HDMI is a pain in the bum to use in a professional theater installation, but to make one able to play DVDs or BDs it's almost unavoidable (are there any disc players in existence that have an HD-SDI output?), and does at least have the advantage of allowing you to take eight channels of uncompressed PCM audio out of a consumer-grade player.
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