Share your knowledge on these two classic MPCs
By taiara Fri Apr 23, 2010 7:37 am
Hello everyone. I just noticed that when I unplugged my SCSI Jazz Drive cable, I hear this loud high pitched noise in my headphones. When I plug my SCSI drive back in and wiggle the cable the noise seem to decrease...
Has anybody had the same problem....I would greatly appreciate it if some one can tell me what is going on with my SCSI + Noise issue... Thank you
By taiara Fri Apr 23, 2010 3:32 pm
Thanks for replying. I do make sure to shut down my MPC when I unplug my external scsi drive...... I can still save and load files but some how it seems slower lately...
What happens when scsi fuse is blown? Do you think mind might be? How can i fix it?
Please let me know. Peace
By MPCHunter Fri Apr 23, 2010 4:31 pm
If the SCSI fuse is blown, the MPC won't recognize some SCSI devices. If you're still able to access your drive, then the fuse may still be OK.

You may have a grounding issue which is causing then noise. Try using a different power outlet in the house to see if the issue goes away. Make sure all the screws inside the MPC are tightened down. You could also be hearing the hum from the inverter, or the EL foil vibrating.
By taiara Sun Apr 25, 2010 5:41 am
Thanks MPC hunter.
I have a new backlight. Also the inverter if fine. seems fine as it isn't making any noise at this point.
I also plug in to Fishermans power conditioner so the power should be clean...
Do think it's some kind of grounding issue with the headphone jack and the scsi port in the back.....
The noise is there when nothing is attached to the port. When I attach the SCSI cable it goes away even with the drive turned off......At least I can work with the drive plugged in. But it's annoying. I've got my MPC supped up with os 3.5. Full 32 megs ram. With new LCD and back light brand new old school Dark Gray Pads....and I want it to be mint.....I guess my dear MP is starting to show it's old age from the inside...
By MPCHunter Mon Apr 26, 2010 2:47 pm
taiara wrote:I also plug in to Fishermans power conditioner so the power should be clean...


Not all power conditioners work the same.

Does your SCSI drive plug into the same power conditioner? Have you tried plugging both into a different wall socket to see if the problem goes away

taiara wrote:Do think it's some kind of grounding issue with the headphone jack and the scsi port in the back.....


The audio ground is an analog ground and the SCSI ground is a digital ground and should be isolated from one another.

Have you checked to make sure every screw in the unit is tightened down? If you have an internal floppy or zip drive, make sure it's tightened down.

Are you sure the EL foil is secured -- it doesn't matter if it's new or now, all EL panels vibrate.
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By The Grublet Mon Apr 26, 2010 2:55 pm
its the inverter, coupled with the scsi being plugged in..

its something with the way the power adapter on those iomega's mesh with the inverter's natural hum.


1- turn off backlight by pressing in on contrast knob... this will cut it down..

2- do all your sampling without the scsi connected.... the scsi was sensitive on the 3k, and for some reason, it even being plugged into the DB25 scsi cable (even without a drive plugged in or powered on) can cause lots of buzz..


see if you have a clean signal by turning off the light and unplugging the scsi


if its still there, get a better, newer power strip.
By oldgearguy Thu Apr 29, 2010 11:41 am
I have the same thing happening. I have a 3000 LE with 3.5 OS. However, I have an internal CF reader hooked through the SCSI chain.

What you are hearing is the sync tone. Plug the headphones in and out a couple times and you'll hear it start to modulate. Then you'll hear a low frequency thumping in the audio L/R jacks.

I am in the middle of debugging it and should have some results this weekend. So far, a simple electrolytic recap of the CPU, Sync, and SCSI boards didn't help. I have some suspicions about the sync getting dumped into the ground plane someplace, but I haven't had time to work on it yet. I might try powering up with out the SCSI board and see if that has any effect.
By taiara Thu May 06, 2010 6:59 am
Thanks All for the advice! I live in Tokyo and I called the good old Akai here in Japan. The guy said it had to do with the headphone ground....Some how he seemed know exactly what the problem was and said that it was a real common thing to happen to mpc3000. I'll send it in and see if it does anything.
Last edited by taiara on Thu May 06, 2010 11:47 am, edited 1 time in total.
By oldgearguy Thu May 06, 2010 11:23 am
taiara wrote:Thanks All for the advice! I live in Tokyo and I called the good old Akai here in Japan. The guy said it had to do with the headphone ground....Some how he seemed knew exactly what the problem was and said that it was a real common thing to happen to mpc3000. I'll send it in and see if it does anything.


While you're talking to Akai Japan, can you please request a set of schematics? I talked to a number of folks inside Akai/Numark here in the states and the word is that basically all hard-copy schematics for the 3000 are back in Japan. Everything that is on-line only covers the disassembly and parts list. There is one PDF of the power supply board. Nothing else.

Finally - if/when it's repaired, can you get a detailed description of the fix? I can look further myself given this info, but if would be nice to also hear from the actual tech that fixed it.

thanks
By MPCHunter Fri May 07, 2010 12:27 pm
oldgearguy wrote: I talked to a number of folks inside Akai/Numark here in the states and the word is that basically all hard-copy schematics for the 3000 are back in Japan. Everything that is on-line only covers the disassembly and parts list. There is one PDF of the power supply board. Nothing else.


Why don't you buy the service manual and schematics for the MPC 3000 that VST is selling on eBay and scan it into a pdf for everyone?
By oldgearguy Sat May 08, 2010 1:06 am
MPCHunter wrote:
oldgearguy wrote: I talked to a number of folks inside Akai/Numark here in the states and the word is that basically all hard-copy schematics for the 3000 are back in Japan. Everything that is on-line only covers the disassembly and parts list. There is one PDF of the power supply board. Nothing else.


Why don't you buy the service manual and schematics for the MPC 3000 that VST is selling on eBay and scan it into a pdf for everyone?


Didn't know there was any for sale.

Done

bought, paid for. I'll let you know when they arrive.
By oldgearguy Thu May 20, 2010 10:59 am
somewhat of an update. I had some more time to check things out. What I'm seeing on my MPC is that the Sync Out signal (on pin 10 of the connector of the sync jack board) is essentially being dumped into the ground plane.

So, if I unscrew the sync jack board from the MPC, the problem goes away. Measuring the voltage on the sync board mounting bracket versus the MPC chassis shows +4.6v DC. On the scope I see a rough triangle wave of about 2v pp AC.

If you look at the schematic for the jack board (labelled page 22, it's the 36th page in the PDF file), you can see Akai has 3 grounds on that board. Regular chassis ground, Analog ground, and a 3rd one labelled FG (floating ground?). From what I see, it looks like the Sync signal (which is a 4v square wave) is being filtered by the resistors and cap on the way to the sync out jack and is showing up on FG as the rough triangle waveform. In the bottom right corner of that schematic, you can see where FG, AG, and GND are all tied together though a pair of 0.1uF caps. That dirty ground is making its way onto that metal bracket and when it is screwed into the MPC, causing the problem.

Since this scheme used to work, I'm still trying to figure out what has failed/changed to cause this issue. The caps seem to measure OK, but I didn't take them out of circuit.

As a perk for reading this far, http://www.oldgearguy.com has a very useful link for those that are techically inclined with regard to the MPC 3000.