CP750 - level drop disease presented shortly after power supply swapout

[Elia Orselli]

At least the adapter cable has a reasonable price, but we have already said many times that CP950 can't be considered the replacement unit for CP750.

Considering the end of the spare MB availability or any replacement program, it would be great if Dolby would release the motherboard schematics. This would at least consider to plan repairs with reasonable worktime and cost, without taking particular market share away from the CP950 (which anyway seems to suffer delivery difficulties like so many other electronic devices)

[Mark Gulbrandsen]

There are a gazillion SMT capacitors on that board. If it is just the few through-hole...then changing those wouldn't be an issue. Depending on how the day goes, I'll have access to the MB today to snap a picture.

I have yet to replace any SMT capacitors in electronics. Almost always they are ceramic and tend to last decades. But if I do, a two leaded device will be very easy to remove and replace.

[Carsten Kurz]

The volume drop issue seems to be quite common (as is the power supply failure). Given the number of CP750 in the field, it would certainly be interesting to find out which capacitors actually cause the issue and why it exhibits a level drop (not very typical in analog audio circuits). I would assume they'd have to be within the analog output section of the CP750, and these post-DAC circuits are usually not overly complex and easy to follow.

[Leo Enticknap]

And, are you really sure that the CP950 won't have cap issues down the road?

If it's like most Dolby digital cinema devices to date, it'll be very reliable for about a decade, and then become high maintenance.

They never seem to get ventilation right. The CP750's problems, IMHO, stem from the fact that there is no fan in it, and that heat management is all via conduction and radiation, with no convection. If it's in a rack that is not well ventilated, in a hot booth and above a stack of power amps, it's gonna cook. The 950 at least has fans in its power supply module.

[Mark Gulbrandsen]

If it's like most Dolby digital cinema devices to date, it'll be very reliable for about a decade, and then become high maintenance.

They never seem to get ventilation right. The CP750's problems, IMHO, stem from the fact that there is no fan in it, and that heat management is all via conduction and radiation, with no convection. If it's in a rack that is not well ventilated, in a hot booth and above a stack of power amps, it's gonna cook. The 950 at least has fans in its power supply module.

Exactly the same problem Panastereo had. Because it was 100% analog, it drew a heavy load on the power supply and it ran very hot, even though it did have a fan. I had to replace a fan in one of the supplies once, and when I looked it up on Digi-Key they had two versions of it available. Turns out Panastereo used the low flow fan. Changing to the higher flow fan completely got rid of failures, which were one of the Bridge rectifiers in the supply Their later power supply versions were more reliable.

[Marco Giustini]

Steve,

Why I admire Mr. Carlson and his deep knowledge on the subject, I am not a fan of the twisting removal of SMD caps. I don't know, it just doesn't feel right and if the cap has leaked I am concerned the mechanical action might cause additional damage to an already-weakened pad. Just my personal preference of course!

Mark,
With SMD caps I think Leo means the electrolytic SMD caps which can and will fail as normal through hole ones.

[Marco Giustini]

Steve,

Why I admire Mr. Carlson and his deep knowledge on the subject,

*while I admire