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

Sarah Thompson plodger at gmail.com
Wed Sep 28 20:58:51 CEST 2016

I'd go poking around with a scope on the SMPTE board, particularly on its
power, to see if something looks funky. It could be that you have a
component failure on there somewhere that isn't showing up in terms of
expected functionality, but is dumping a load of noise into the power (or
some such). I've seen that once before with a latch that was out of timing
spec on a SCSI interface that was dropping huge but incredibly short
glitches into the power that weren't visible at all without a fast (400MHz)
'scope -- our 20MHz cheapy made the power look totally clean.

Good hunting!

On Wed, Sep 28, 2016 at 11:48 AM, Michael Taylor <mtaylor.tech at gmail.com>

> I just wanted to say thank you to all the people who responded with
> helpful comments.
> It turned out that it had nothing to do with ground bleed whatsoever. I
> was actually getting bleed from the SMPTE I/O board and it was polluting
> the A/D input circuit. I unplugged the ribbon cable from the SMPTE I/O
> board to the CPU board and my MPC is now quiet as a mouse.
> Unfortunately, the current online service manual doesn't seem to have
> anything for the SMPTE I/O board. Am I missing something, or is it not
> there?
> Anyway, I am super thankful to have the machine up and running again.
> it is easy to take music making for granted when we have access to so much
> music making technology from the last 50 years. It is good to be forced to
> take a break against your will for a couple of months.
> On Sun, Aug 28, 2016 at 7:40 PM, Michael Taylor <mtaylor.tech at gmail.com>
> 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.
>> 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.
>> -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.
>> -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?
>> 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.
>> Thanks,
>> Mike
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