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MP-2 S/N 501251 from eBay for parts or repair

Started by Gregg, July 03, 2024, 08:42:36 PM

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My next eBay adventure arrived today. Did a quick assessment.  Not in as good a shape as 501360. Transformer was held in by 1 screw and smashing around the battery and CPU.  Front panel display mounts had detached.  Signs of rework around the battery, again.  C104 dented by the transformer. No other obvious issues. 

For the curious: MP-2 501251 folder



Hey Gregg, it's had a bit of a hard life by the look.  So v1.33 EPROM, that's pretty early IIRC.  Oh well, you did buy it for parts.  The again, you can probably get it going again ?

The transformer smashing around and subsequent damage I can kind of get, albeit not good.  Not sure what they did to make the display mounts detach :crazy:
Studio Rig: Stuff; Live Rig: More Stuff; Guitars: A few


This unit while having had a rough life is now half alive.  The digital section boots and the panel responds to button presses.  It did take some TLC to get it this far.  You can see my repair log below.  Just need to mount the transformer and display properly before checking out the audio section.  Blocked waiting on parts.

Added some more pictures of my rework to the Dropbox folder here: MP-2 501251 folder


Repair Log 501251
  • Removed

    • Cut out the soldered in battery
    • Transformer
    • Front panel display
    • Power cord, mains ground to enclosure bond, and strain relief.
    • Fuse holder - ¾" deep socket for nut. Tighten before attaching hot (black) wires. 
    • Power switch
    • U117, P8031AH MPU - all pins at an angle due to transformer bumping it. 
    • D910 - smashed to shit
  • C103 Removed, tested ok, reinstalled
  • Fixed broken trace between battery ground through hole and C103's ground trace. 
  • Transformer voltages - check

    • Yellow - 8.56 VAC
    • Orange to Orange/White (CT) - 16.8 VAC, 16.8 VAC
    • Orange to Orange - 33.6 VAC
    • Red - 202 VAC
    • Blue - 15.44 VAC
  • Power supply - check

    • Vcc1 U905, 7805 (5V) - pin 1 input, pin 2 GND, pin 3 Output, XFMR yellow: 5.01 VDC
    • Vcc4 (SRAM battery 5V / 3V - 
    • Filament (12 VDC) U904, 7812 - pin 1 input, pin 2 GND, pin 3 Output, XFMR blue: 11.86 VDC
    • Vcc2 (+15 VDC) U902 7815 - pin 1 Input, pin 2 GND, pin 3 Output, XFMR Orange: 15.04 VDC
    • Vcc3 (-15 VDC) U903 7915 - pin 1 GND, pin 2 Input, pin 3 Output, XFMR Orange: -15.08 VDC
    • +24 VDC U906 LM317T - pin 1 adjust, pin 2 Output, pin 3 Input, XFMR Orange: 23.71 VDC
    • -24 VDC U901 LM337T - pin 1 adjust, pin 2 Input, pin 3 Output, XFMR Orange: -24.01 VDC
    • Line HV (+190 VDC) - at test point, XFMR Red: 195.5 VDC
  • Removed U117 socket
  • Removed D907, 1N4007 - deformed but tests OK.  Replace.
  • Straightened MPU pins - ok for reuse. 
  • Replaced R913, 240k ½ watt, & C912, 33µF @ 50V, to fix HV - HV at 191.4 VDC
  • Replaced C104 (33µF @ 50V), D909 & D910 (1N4148) - physical damage
  • Replaced tube section noise mod caps, C333, C324, C912, C334, R913
  • Cleaned fuse holder and switch.
  • Replaced D907 (1N4007) - physical damage
  • Replaced MPU socket @ U117.
  • Reinstalled P8031AH @ U117.
  • Off board battery holder modification and damaged trace restoration. UV solder mask applied.
  • Digital section of the MP-2 appears functional - boots with no issues.  Battery backed up SRAM OK as well.


Hey Gregg, well you seem to be getting there.  Lots of stuff to fix, I'm still wondering how it got like that :crazy:
Studio Rig: Stuff; Live Rig: More Stuff; Guitars: A few


Decided to finish up the last few details and test the analog section of this MP-2 since I would have time to work on the audio section this weekend...

  • Mounted display.
  • Reinstalled transformer, fuse holder, power switch, power chord, cleanly.
  • Installed tubes
  • Tested analog / audio section. - tests OK

Sounds like I fixed it.  @rnolan can you give a listen to this, 501251 audio test, and let me know if it sounds about right to you.  Also wouldn't turn you down if you made a few more raw and processed test files for me to use to validate my work.

Graphic photos of my work along the way can be found here: MP-2 501251

@MarshallJMP - what sort of test suite should I have to convince myself that a unit is fully working?  I may decide to sell these 2 units and don't want to mislead anyone.



Hey Gregg, seems to be working fine, well done.  Another rescued MP-2 :woohoo2: .
Sound check procedures

To check everything is working will take some time.  There are lots of features.  The sound check proc pdf from ADA is very light on (albeit a good start).  Also depends how thorough you want to be.  I've put some ideas below for you trying to keep in mind what you have at hand (e.g. another MP-2, which in "Panel" mode will/can act as a midi switcher for program changes).

So you'll need a midi controller of some sort.  If you used the MP-2 editor on a Win PC (as it needs .NET) and a USB midi interface (I bought the Rolland one) you can exercise allot of the functions, e.g. program change, dump/load to PC. The USB midi interface has 2 midi leads, 1 for midi in and the other for midi out. To test midi through you could connect the midi through to the midi in on another MP-2 which should also change patches when you send program change messages from the editor.

To test the Fx loop (which is a stereo parallel loop) you need some thing to put in the loop.  There should always be signal from the loop sends, to test the returns and the return mix levels (which default to 25% on a new blank patch) you need some sort of Fx unit, at a pinch you could use another MP-2 in the loop, on a different patch e.g. say you have a clean patch selected, if you select a dist patch on the MP-2 in the loop it should mix in at the mix level set.  As I said at a pinch this will work but set the loop gains to inst level, not line. And you'd test each loop separately.

To test the cab sim/emulation outs you need to test each channel jacks and XLRs and that the switches work (2 x 12 cab/ 4 x 12 cab), line/inst level on the XLRs.

Testing the RTM (real time midi) is a bit trickier. If you've used the editor, that you can change a parameter on the PC screen and the unit responds proves some of it.  But the RTM is mostly controlled by a midi expression pedal and/or switch pedal (e.g. ADA Quad switch).  E.g. wah sweep, stereo volume control (defaults to #31), parameter editor (also defaults to #31).  The #xx are the RTM continuous (CC) number assignments.  So each RTM controller (exp pedal or switch) is assigned a number (#xx) which you assign to a parameter in the MP-2 e.g. Switch RTMs - Wah on/off (#72 IIRC) or loop in/out, chorus on/off etc. Expression pedal RTMs - OD1 level, Stereo Volume, Wah sweep, chorus rate etc.

Have a read of the ADA MXC manual (attached).  That's the pedal (pack) it came with and I use.

The MP-2 also includes some "macros" which I've not explored yet.  But they are basically combinations of the various RTM assignments (i.e. move one expression pedal and a few parameters change together), so if the RTM stuff above all works, then the macros should also.

Midi mapping, this probably needs a midi controller to test?.  Or you can use a separate MP-2 in "Panel" mode as a basic controller. In Panel mode, if you change patches on the front of the MP-2 (panel), they are also sent to the midi out.  So you connect the midi out of 1 MP-2 (Controller/panel mode selected) to the midi in of the one in test.
So this is where the MP-2 receives a program change number but selects a different internal patch number, and/or the MP-2 sends a different program change number to the midi out (to say a Fx device).

Studio Rig: Stuff; Live Rig: More Stuff; Guitars: A few


Well I think Rnolan answered your question already.  :cool:


rnolan - thank you for the comprehensive answer.  I will need to take some time to process it all and get started.  I have read the burn in and sound check docs from ADA... very minimal stuff there. Clearly assumes their lab setup, but a start none the less.



Hey Gregg, no worries :wavingsmiley: I hope it helps.  if you haven't already, it's worth reading the user manual (albeit not a quick read).

I tried to think of everything you'd need to check, I hope I didn't miss anything important.  But if you can attest that all that stuff is good to go, that's way, way more assurance than a prospective buyer would normally get.  Moreover, if you bought a 2nd hand MP-2 some of those features (if there were issues) would/could take a while to discover, and some of course would be in your face quite quickly.
Studio Rig: Stuff; Live Rig: More Stuff; Guitars: A few


I have read the MP-2 manual several times and started reading up on how MIDI works and what all the terms are along with the various bits of software out there.  Think I have a good idea how to exercise the MIDI section of the MP-2 now based on all that research / reading.  Still don't have a solid test plan yet, but when I do, will share here for feedback.



Hey Gregg, I thought you may have read the manual :thumb-up: .
The hardest part to test is the RTM stuff since you don't have a midi controller.  A cheap way is to pick up a Behringer FCB1010 (https://www.behringer.com/product.html?modelCode=0715-AAA).  They are not particularly expensive and have all the things (and more) you'd need to exercise the RTM functions.  Alternatively (albeit maybe a bigger rabbit hole) is to use some recording software that lets you record and edit midi (a midi track).

Then again, this is way more testing than I've ever seen anyone bother with (not that you shouldn't BTW).  Generally, if it makes a (reasonable) sound and the outputs work, they say it's good to go.  Moreover, of all the MP-2s I've picked up over the years, they have never had any issues with the RTM side of things.

But hey, you are an engineer, the requirements are in the manual, so lets develop a proper test plan (happy to help BTW).

An interesting (potentially) aside, I gave a friend (who likes assembler etc.) a copy of the 1.31 and 1.41 hex tonight and he's started to reverse engineer it (I suspect from his initial look that adding additional patches wouldn't be difficult).  I also sent him some schematics so it makes more sense.  Who knows, maybe we can optimise the firmware (not sure what I'd want to change), but it would be nice to develop a pseudo code algorithm.  Who knows, maybe we could develop a delay + reverb mod to include :dunno: .
Studio Rig: Stuff; Live Rig: More Stuff; Guitars: A few


My plan was to write some code to exercise the RTM MIDI functions and anything else I couldn't find open source for. There are some libraries out there already that should make it easy to write a test suite for Linux / a Raspberry Pi from what I saw.

Please connect your firmware friend with me.  I have done some preliminary reverse engineering work / notes that he probably doesn't want to have to figure out from the schematics.  I haven't made any tangible progress reverse engineering the firmware mostly due to lack of time, but have a memory map derived from the schematics.



Hey Gregg, no worries, PMs and emails sent to connect you and I also included MJMP.  Also I'll try to bing Laurence (my friend) up to some understanding of the "why" (what's it all about Alfie), he's not a muso but he likes assembler.
Studio Rig: Stuff; Live Rig: More Stuff; Guitars: A few