Let's Get Technical > All PREAMP Tech Tips & Support
MP-1 wierd midi problem
MarshallJMP:
Can you try something, find a patch with chorus in it, then plug in the midi pedal and listen if the chorus keeps on working? Listen to the modulation, make sure it doesn't do funky bussiness.
Now all the control logic for the midi is on the main board, could be there is something wrong there.
rnolan:
OK, turned it on, selected #9 Over Chorused Clean, sounded fine lots of chorus. Plugged in MXC, MP-1 went to #1 so normal. Pressed 9 on MXC about 10-15 seconds later MP-1 changed to #9, chorus still fine, no funky business. Pressed 8 on MXC, MP-1 went to #4 after about 10-15 seconds. Turned everything off except MP-1, so MXC still plugged in but no power to it. MP-1 stayed at #4 for a while (while I type this post), I just turned around and checked it, MP-1 now changed to #1 (MXC still plugged in but powered down). Pressed MP-1 Up button, display flickers between #1 and #2 while the button is pressed then back to 1 when released, if I hold the Up button on for a while, it flickers between #1 and #2 a number of times after I release the button (like command is in a buffer?). Pressed MP-1 #3 button, display flashes 3 while pressed then back to #1 when button released (but doesn't flicker between #1 and #3 like Up button). Unplugged MXC and cycle MP-1 power, now front panel buttons work as expected. Plugged the MXC 7 pin cable back in but no phantom power, MP-1 continues to work properly. So powering up MXC when connected starts the funny business which doesn't go away until MP-1 rebooted.
MarshallJMP:
Very strange indeed. What happends if you do a midi dump, store bank+6 ? Try it with out the mxc and with.
Maybe a long shot but sometimes it helps when you have strange problems, reset the RAM chip. Either disconnected the battery or pul the RAM (6264 or 5864) chip out.
Now this will erase all your presets.
Can you get your hands on a scope? Maybe we could do a skype session?
rnolan:
Hey MJMP, so midi dump displays sending all both with and without MXC. I pulled the battery (it's in a holder :thumb-up: ) and reset RAM. Did C 1 to whatever then error 1, 2, 3 and settled. It's still weird :facepalm: . So I press MXC 9 and about 15 secs later it changes. So all changes from MXC press take quite a long (but similar) time. But still weird as MXC 7 eventually changes to 3, and MXC 5 goes to 1 (mapping is 1:1 BTW). So it does change programs eventually but not always to the selected number :crazy: . To do a scope/skype session I'd need to do it at Tim the techs, he has a scope. I'll call him and see what we can arrange.
MarshallJMP:
Did you check if it actually sends something? Do you have a soundcard with midi in/out or one of those usb to midi things?
Some things to try out, reseating the grey cable from the mdi board on both ends. Reseating the uart chip (the 40 pin chip on the midi board), the opto (usually a pc900 or a H11L1, 6 pin) since these are in sockets. Swapping the eprom. Reseating the Z80 and RAM. Probably won't do anything but it doesn't hurt to try anyway. On pin 4 of the opto you have 5V if no midi comes in.
Things Tim could check with his scope, making sure the clock for the Uart chip is 500.000 kHz (this determins the baud rate), it's on pin 17 and 40 on the uart chip. Also have him take a look at pin 16 of the Z80 if you have interupt pulses there. Let him look at it without the MXC and with and see if there is a difference. Look for the Tick pulses on pin 4 of U6 (74LS08) on the midi board. Check if the strobe lines to the midi board are working, see schematic of the midi board (TXDT STB,CTL STB,ST STB RX DT STB) these are all active low. So is the interupt. Now in normal circumstances you will see only the ST STB go low, very small pulses going from 5V to 0V, tell him to set the timebase of the scope to 500µS, you should be able to see them.
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