CP750 level drop disease

[Carsten Kurz]

Dolby demands internal temperatures within the CP750 to not exceed 35 degrees C/95 degrees F. That is ridiculous and an obvious design flaw.

- Carsten

[Marcel Birgelen]

I guess that's pretty unrealistic, as there will always be surfaces inside the box that exceed that value after prolonged use, even if you put it in an air-conditioned room with good airflow.

If the problem isn't just in the big caps, but also in many of the smaller surface mounted ones, I don't know if it's really worth it to do a full re-cap, unless you're really a soldering ninja and/or have the right tools, like a reflow oven...

[Steve Guttag]

We've always had good spacing around the CP750 (and all other sound processors...even in the CP200 days, we always put a space between the chassis) and we've always tried to put fan panels in each rack to pressurize the rack...not just for cooling but to also keep dust down..it won't settle in the rack if there is even a slight bit of positive pressure in the rack.

[Dave Macaulay]

After several CP750 repairs, I've seen sòmething of a pattern. Most have had low level and run hot - the psu heatsink plates get hot quickly.
The +5 & +15 supplies are ok but -15 is up to -20 (could be reversed... the15V line farthest from the end green on the board connector goes high).
Replacing the psu and board fixes it. The +5 current doesn't change, about 700mA on powerup jumping to 1.7A when the relays pull in. The psu heatsink plates get warm but nowhere near as hot. I have not measured the +/-15 current.
Can't say if the overvoltage causes the level drop but maybe? If you have one that gets overly hot at the psu end, probably this overvoltage is happening.

[Leo Enticknap]

Dolby demands internal temperatures within the CP750 to not exceed 35 degrees C/95 degrees F. That is ridiculous and an obvious design flaw.

It would be a lot less ridiculous if they'd put an exhaust fan in the case.

[Ronda Love]

Thank you for all the thoughtful input, gentlemen. We will have a few 750's available to test the recap on if someone is interested and can give me a quote? We're in PA. Should be able to ship out in a few weeks.

[Tony Bandiera Jr]

Thank you for all the thoughtful input, gentlemen. We will have a few 750's available to test the recap on if someone is interested and can give me a quote? We're in PA. Should be able to ship out in a few weeks.

If I had the proper soldering equipment for SMD, I would take on a unit to test. I have plenty of time since I retired.