CP750 level drop disease

[Dave Macaulay]

We're having multiple CP750 processors have the output level dropping away. The affected ones are all around 10 years old although we are just starting to do SPL vs level fader checks on all rooms with them... complaints started from a site built and equipped 10+ years ago. The only cure is a new main board.
I'm not complaining that a decade old electronic device fails, although we shouldn't need to expect that.
Just a heads up.
On a few with the alignment channel faders at 100% (16) I have seen surround SPL under 70dBC. Screen channels haven't been as bad, some around 80dBC max. Still unacceptable but tolerable for a short time pending main board replacement - a bunch are on order.
Dolby sent a notice advising that this can happen and links it to overheating exacerbated by blocking the cooling holes in the chassis - there should be open or blank rack space above and below the processor and it should not be above a hot component. At this site they are above a monitor and below a DCP2000 (neither gets hot) with one RU open above and below in well ventilated cool racks.

[Carsten Kurz]

I heard that quite often - know that some sites solved it (at least temprarily) by open the case or pulling the CP750 out of the rack and applied an external cooling fan. Would be interesting to learn what exact component causes this, as it would probably be easy to solve somewehere around the analog voltage regulation for the output stages.

[Steve Guttag]

At this time, we have not experienced the problem but know others that have. probably 95% or more of our CP750s have nothing above them and, at least 1U and often more below them (usually due to what they replaced that was 3-4U tall and they had a space. We also have, traditionally air cooled our racks with forced, filtered air. So that may have something to do with it.

It should be noted that the CP750 motherboard does NOT ship with the current firmware...it ships with some sort of goofy preload so always be prepared to load in the firmware.

[John Thomas]

We had a CP750 do this -- but it lives in a road case and only gets powered on and used a few times a year. So I can't say that prolonged heat exposure is a likely cause, but it was definitely used in some hot booths/environments.

Agreed Carsten, I would love to know the component so I could fix this myself.

[Marcel Birgelen]

A few months back, in the midst of the local lockdowns, I fixed a broken CP750 myself. It was more luck than really something else though. The device didn't want to boot anymore, so I took out the motherboard and tested all the components I could test with my measuring gear. I didn't really find a single component that seemed to be faulty, as far as I could test it. I bought a new ESR meter to test all the caps, in the end, not a single cap really qualified as bad, but I decided to replace all the "worst" caps I could find. To my own surprise, it worked and for the limited tests I've been able to do with it, it seems to be fully functional.

So, if the plan is to replace the motherboard anyway and you have some time at your hand, maybe you could do about the same with this particular problematic CP750. Obviously, if the problem is inside a complex IC, chances of finding the sources are pretty slim, although relatively simple voltage regulators are pretty easy to diagnose.

[Leo Enticknap]

This is a known issue, addressed in Dolby Field Bulletin #265. I tried to upload it here, but can't, because the PDF exceeds the size limit. Basically, it tells you to replace the mommyboard, and gives you an illustrated guide to doing so.

I haven't had any cases of level drop disease recently, but I have had a spate of CP750 power supply boards biting the dust with burst output capacitors, all of them in units manufactured in 2013 and 2014. Worryingly, in one of them, I replaced the power supply board, and the unit went bad again about 10 days later. The replacement board was still fine - it was the motherboard that was bad.

[Mark Gulbrandsen]

Went through a similar thing witj XD-10's and CP-650 power supplies back about 2008. Capacitors failed after the units had been in about 5 or 6 years. I simply recapped the motherboard and power supply board on site when this happened and put them right back into service. I carried kits of capacitors once it began to look like it was going to have to be done frequently, lots of both units had been installed.

[Greg Routenburg]

Replacing the CP750 motherboard is kinda silly in my opinion. The board costs greater than half the price of a new CP anyways which makes sense in that it's the only freaking board in the thing. You may as well toss in a new PS in the interest of doing the thing right while you're schlepping all the way to God knows where to do the work and things get marginally pricier yet. Even though the CP750 has proven to be a decent little processor for what it is, my feeling is that, unless you need the multichannel analog input, you'd be better just biting the bullet and relacing it with a CP950. That's assuming you wanted to stick with Dolby.

[Steve Guttag]

So, in addition to the multichannel input...there can be a host of other reasons for sticking with the CP750...let's start with, you don't have to retune the room as well since the old settings may be merely transferred. You may have an automation system that knows the CP750 commands and would need to be revamped for the CP950 (presuming sticking with Dolby and obviously if you are not)...You don't want to rewire EVERYTHING to accommodate a new processor (the CP950 has not only completely different pinouts but transposes which side everything is so even power cable routing may need to be changed). you may be using the TOSLINK input...strange as it may sound...I've found some of the satellite boxes will have TOSLINK but coax...and the list goes on. Why spend double to get a new CP when you may not be using any of the "benefits" of the new CP? If spending half on a MB gets you another 7-10 years on the processor...that gets you 14-20 years on a CP...not too bad.

Certainly, one can make a list of what one gets with a new CP and then look at both lists and then decide what makes the most sense for that particular situation.

[Leo Enticknap]

Agreed. The problem with swapping a 950 for a 750 is that, as Ving Rhames put it in Pulp Fiction, doing so is "pretty f***ing far" from plug and play, as Steve describes. Replacing a 750's motherboard is an hour's work with no need to disrupt anything else, whereas installing a 950 involves new wiring, retuning, and reconstructing its interaction with other devices in the overall system. As against which, Dolby has announced the end of parts support for the 750, in, IIRC, 2025, so the planned replacement of 750s in service makes sense from that perspective. But of course if the power supply board or motherboard dies, what you do next is an emergency response in which a day's work rather than an hour's could mean several lost shows, not planned maintenance.

[Dave Macaulay]

Curious where Greg is getting a CP950 for only twice the price of a CP750 mainboard...

[Greg Routenburg]

All excellent points Steve. There would certainly be some considerable work to doing the switch over. Something just doesn't sit right with me when you talk about replacing a defective product with another that likely has the same defect. It seems like a waste of money that you'll ultimately need to spend again anyways just to prolong the life of what you have. I'm not suggesting that the 950 or whatever you choose to install doesn't have it's own potential and unforeseen problems but one hopes that Dolby will make an effort to try and resolve them rather than say. "Here's an expensive band-aid for a solution that we don't have any interest in actually fixing so that you'll buy more of our stuff in the long run anyways." By that logic, one should really dump the Dolby enitrely I guess and install soemthing like a Trinnov or QSC solution and be done with it but that leads to other challenges. I don't know, should CPs be considered consumables now? I have a hard time accepting that.

[Steve Guttag]

EVERYTHING is a consumable now. And, I can tell you...ALL of the CP choices you have now (and likely in the past as well) had defects (er..."features."). As for putting in a motherboard that could kick the can down the road 7-10 years (and again, I have a LOT of CP750s in the field without the issue, thus far) may exceed the life of the business and may get you to a better technological state than we are now. The CP750 has features that the CP950 does not have (and vice-versa, naturally). As for product support, I have no problem with Dolby, personally. They have always backed up their products...sometimes better, sometimes worse. I can say that I really like the crew they have presently.

As for other CPs...what is out there? Trinnov...that is going to be a significantly higher cost solution and one would hope that with that you would be going for the better sound tuning capabilities. QSC...there is the DPM line...talk to those that have it and decide if it is for you. The DCP line...pretty ancient stuff and likely not too long for this world now. JSD...why? It is also getting older in design, it would be a complete rewire and likely not to have a huge number of years left (QSC has shut down most of what they acquired from USL) and, of course Q-SYS...well yeah...that can do a lot but like Trinnov you are not going to just casually and inexpensively move in that direction. Q-SYS is definitely the direction I'm going for new designs.

So, though it may rub you wrong, I'd say that the overwhelming majority of time, at this point, replacing the motherboard in the CP750 is going to make the most economical sense for the business.

[Marcel Birgelen]

There is also still Datasat... We've been using an AP20 for years and never had some real issues with it. Most places I know never had a single show lost due to a problem with their AP20. The biggest problem I have though, is that Datasat Digital isn't its former self anymore, since ATI acquired them.

I guess the future are systems like Q-SYS, especially since this pandemic will probably force many theaters to rethink their business strategy. Since most theaters have gone exclusively digital, there is no more real movie magic here anyway and converting something from AES or other digital interface to analog audio and doing some processing on it, can be done with plenty of other stuff out there... I predict that over the coming years, "movie sound" will enter the main-stream. Maybe with a handful of exceptions, gone will be the days where manufacturers produce specific audio solutions for cinema.

[Greg Routenburg]

As for product support, I have no problem with Dolby, personally. They have always backed up their products...sometimes better, sometimes worse. I can say that I really like the crew they have presently.

Generally, I would say that Dolby has some of the best support in the industry. I guess what I'm saying is, if they want you to buy a new motherboard to address the issue, at least fix the problem on the replacement boards that people will be buying. If they suffer a different failure down the road then so be it but to charge someone for something that has a known, all be it potential, catastrophic issue without even attempting to fix it seems a little lame.

JSD...why? It is also getting older in design, it would be a complete rewire and likely not to have a huge number of years left (QSC has shut down most of what they acquired from USL)

The JSD products have actually been quite respectable in their longevity and were always a good alternative to Dolby by my way of thinking. You're right though, Trinnov and Q-Sys are a big step out of the 750's league as far as a direct replacement. I don't know what you have against the JSD series. The JSD-80 and jointly the rebranded DTS-XD10P were probably one of the most robust digital processors that I've ever personally installed. Aside from the odd power supply issue, they've been rock stars. The JSD-60 is a little anemic but a good value option and the JSD-100 is as feature rich as the 750, if not slightly more. Hopefully QSC keeps them going.

Q-SYS is definitely the direction I'm going for new designs.

Me too. I think it's a great system. It will certainly be the first thing I look at for all new builds going forward.