Dolby CP 750

[Mark Gulbrandsen]

That's the PSU... not the CP750 board. A Dolby tech told me the level drop could be fixed by replacing those many little caps. On a multilayer board... no, thanks.

No, that's a CP-650 power supply, and just one end of the board.

As far as new I wouldn't waste my time with Dolby any more, unless you are going to convert to Atmos. Move your theater forward in time a couple more decades by purchasing a Trinnov Ovation 2 instead. It's light years ahead of anything Dolby offers today.

[Marcel Birgelen]

Has anyone ever tried connecting an external power supply to a 750 using the backup power supply connector on the back of the chassis? Does it functionally bypass the internal supply? If the internal supply was completely removed, would it work exclusively with the external supply?

It should bypass the internal supply even if it's non-existent, it's a backup power supply.

I think the level drop is caused by resistors going out of specs - not capacitors. Those would be smd resistors. Never replaced them myself though

It's in the capacitors... and while some of the surface mounted capacitors may also have gone out-of-spec, simply replacing all the "big ones" on the board usually does the trick. I've done so myself now a few times. I'm also under the impression that those tiny SMD capacitors don't age merely as badly as many of those bigger ones, as those smaller ones are usually made out of layered ceramics, while the bigger ones are often made out of cheaper materials like paper...

I do know a few soldering Jedi masters that can solder SMD components by hand, but I myself am not such a Jedi master.

[Steve Guttag]

The External CP750 supply (which is identical to the internal...just has a case and connector) will power the CP750, even if there is no internal supply.

[Mark Gulbrandsen]

It should bypass the internal supply even if it's non-existent, it's a backup power supply.



It's in the capacitors... and while some of the surface mounted capacitors may also have gone out-of-spec, simply replacing all the "big ones" on the board usually does the trick. I've done so myself now a few times. I'm also under the impression that those tiny SMD capacitors don't age merely as badly as many of those bigger ones, as those smaller ones are usually made out of layered ceramics, while the bigger ones are often made out of cheaper materials like paper...

I do know a few soldering Jedi masters that can solder SMD components by hand, but I myself am not such a Jedi master.

Yep, and most of the SMD capacitors are ceramic, or tantalum and not electrolytic, although there may be a few exceptions. So not much if any SMD soldering should be required. But if you've never done it, lots of patience, temp controled soldering iron.and appropriate tips for the size of the SMD parts solder wick or solder sucker, and an old SMD PCB to practice removing components from, will be needed. I have assembled quite a few SMD projects of my own, mainly Audio DAC', but have never had to repair them. They have no analog output stage, and other than the power supply, there are no electrolytics.They use Lundahl line transformers instead...

[Steve Guttag]

If you REALLY want to get into SMD...having not only appropriate tips for a soldering iron (think small) but also a heat gun (not for heat shrink but for PCB work) and the rework (solder sucker) all all good things to have. Tweezers and a Fume Extractor are also good things to have. A company like HAKKO has most everything one needs, at reasonable prices but you'd not want to buy all of that stuff for just one project. Also remember, lead-free stuff melts at a lot higher temp than leaded solder. You'll also want a good supply of flux when working with a heat gun (some like to use external flux when doing normal through-hole soldering too rather than rely on what is in the core of the solder. Though not need to do these capacitors, if you end up doing any serious rework with SMD...a microscope is also in your future.

[Mark Gulbrandsen]

One thing I forgot to mention isto order 105C rated capacitors to replace what are very likely only 85C capacitors. The 85's are standard. Bot the 105's will last much much lInger...