[sdiy] Does anybody have a BOM for the MPC3000 power PCB and power filter PCB?

[Gordonjcp]

On Sun, Aug 28, 2016 at 07:40:06PM -0400, Michael Taylor wrote:
> Hey all,
> 
> I've decided that it's finally time to recap the power supply on this
> MPC3000 due to weird ground noise issues.
> 

That won't help.

> The MPC is very quiet when not in use, or when playing back preexisting
> samples. When you put it into sampling mode it is quiet until you plug in a
> cable and then it has a very loud high pitched buzz. The cable does not
> have to be connected to anything, just the act of plugging in a cable
> starts the MPC buzzing. Pull the cable out and it's quiet again.

That's a ground loop, not a power supply problem.

> -This has happened in my studio and at the workshop at my job(separate
> buildings about 1.5 miles apart).
> 
> -This is not transformer buzz or a whine from the inverter(the transformer
> is physically silent and the inverter is a separate sound that stops when I
> shut off the LCD backlight).
> 
> -This issue has arisen in the last six months, it was relatively quiet
> before that.

What else has changed?  Electrolytics take about 60 years to fail, not six months - well, except for cheap shitty switched-mode power supplies, in which case they fail quickly and fail hard (lots of smoke and noise).

> -This happens with no other connections that a 1/4" cable and the
> headphones or stereo outs to a mixer(IOW SCSI is not part of the picture
> and this happens with or with a SCSI drive connected).
> 
> -This sound is present in all new samples that are recorded while there is
> a high pitched buzz. You can sample silence, and the MPC will be silent in
> playback mode and then you will hear the buzz when you play the sample and
> then silence after the sample stops.
> 
> -The MPC sequences midi, accesses a SCSI CF drive, and plays back
> samples completely normally outside of the sampling issue.
> 
> So my two questions are:
> 
> Can you guys think of anything else I can do to trouble shoot this issue
> besides redoing the PS boards?

Leave the power supplies alone, unless you are *certain* the fault is there.  "Re-capping" always causes more problems than it solves, which is why I automatically charge an extra 200 quid to fix anything that's been "re-capped".  First I've got to fix all the introduced faults, then I've got to fix the original fault...

Look again at what you've got it wired to.  Are you sure the noise isn't coming from the device you've got it plugged into?  Have you tried an audio cable with the ground lifted at one end (you can stick a resistor across if that makes you nervous).

> Does anybody have a preexisting BOM for the caps on these PCB?
> 
> I have the service manual, but the parts listings are cryptic for some
> parts and completely missing for others.

You could just look at the components on the board, if you insist on going down this route.

-- 
Gordonjcp MM0YEQ