MPC3000 PS issues

Hi there, I've spent the better part of two days reading schematics. I've got a question for you all. I bought an MPC3000 from a pawn shop. I noticed the backlight wasn't working, so I ordered a new EL panel. While waiting for the EL Panel to arrive, I thought I should check the voltage from the filterboard - weird voltages.

Normal:

PIN 1 = +5V
PIN 2 = GND
PIN 3 = -12V
PIN 4 = AGND
PIN 5 = +12V
PIN 6 = +5V

Mine one of the 5v lines wasn't working and there was a lot of ac ripple.

The black cable from the mains transformer showed signs of burning, there was lots of strange stuff going on- bad solder, shorts + what have you.

My question is: What are the voltages to be expected coming from the mains transformer and if it's not putting out the right voltages, where can I get another?

Was the machine working or not?

Sorry, yeah...Everything works except the backlight (actually haven't tested scsi). I just cleared the shorts and now there's 8 volts coming out of one of the 5volt rails. The inverter is still not putting out any voltage. It's alright, I ordered a 12volt inverter for the replacement EL film I ordered. I'm going to hang it off of the 12volt rail.

aftermarket 12 volt inverter inside the MPC3k. Can anyone think of any reason that's a bad idea? They're tiny and there's plenty of room in there.

noiseybeast wrote:aftermarket 12 volt inverter inside the MPC3k. Can anyone think of any reason that's a bad idea? They're tiny and there's plenty of room in there.

Any reason why you would not just use the original part ?

VST sell them:

http://www.vstservice.com/p-585-akai-backlight-inverter-block-lcd-for-mpc3000-others.aspx

In addition.

I suggest after reading your posts that you focus further repair attempts on returning the power supply function to its original state.

With the parts as factory designated.

Just a thought.

Rohan.

mpc3000le wrote:Any reason why you would not just use the original part ?

Because the 12vdc EL inverters only cost $10 including shipping. Why would I pay more for something just to have it stock?

The only non functioning thing is that 5vdc rail for the stock inverter. It puts out 8vdc instead of 5.

I still don't understand what was wrong with the power supply in the machine.

Are you one of those people that gets carried away when they see components they could mess with?

clint246clint wrote:I still don't understand what was wrong with the power supply in the machine.

Are you one of those people that gets carried away when they see components they could mess with?

Not at all. Like I said, I noticed that the backlight wasn't working. I ordered a new EL-foil before realizing it could be an inverter problem.

I checked the voltage coming out of the inverter, nothing. I then checked the voltage TO the inverter-nothing. I then began tracing the voltage from the power supply. As far as I could tell the mains transformer put out the proper AC voltages. It was then I noticed that there was a solder blob on one of the voltage regulators on the power pcb. When I cleaned up the blob, I tested the voltage again and one of the lines that should have been putting out 5vdc was putting out nearly 9vdc-the line coming from d801. The regulator is still not putting out proper voltages.

I figured rather than replace a whole bunch of components, I could just hang a new inverter off of the existing 12 volt line and call it a day-especially after reading that a lot of after market inverters make a NASTY whine.

Aiight, do what you gotta do.

Let us know how it goes with the backlight repair.

noiseybeast wrote:

mpc3000le wrote:Any reason why you would not just use the original part ?

Because the 12vdc EL inverters only cost $10 including shipping. Why would I pay more for something just to have it stock?

The only non functioning thing is that 5vdc rail for the stock inverter. It puts out 8vdc instead of 5.

Given that you are capable of measuring power supply ripple then I will make the following suggestion ...

Work on repairing the unit correctly.

Kludging a fix where another problem still exists is never a good idea.

Maybe post some hi-res close up pictures of the various power supply boards in your machine if you think some of us on this forum may be of more assistance.

Otherwise ...

You have the schematics and service manual.

Over to you.

Good luck either way.

Rohan.

So you're saying I shouldn't replace the whole power supply with modded PC power supply? It'd be easy enough to do, there's enough room and you'd never have to worry about sourcing alesis parts again.

Think about it: Modern components rated at higher wattage than the stock stuff, easily sourced if something goes wrong, ability to go between US + Europe with no effort, multiple 5 + 12 volt lines.

I'm only half joking. Think about the implications of pulling the aging + hard to source Akai specific transformer + filter board out and finding a nice quite micro ATX/nano itx board. Voltage is voltage, right?


BTW, those of you who like crunchy sampling rates, it's easy enough to replace the clock crystal with a variable oscillator that can sample down to ~2khz if needed.

An example on an Akai S20

http://www.youtube.com/watch?v=Q22_oxeIDlo

I'm going to DESTROY this thing. I think...