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The Stec Records Forum  |  Audio Gear  |  MPX G2  |  Can't Exit Edit Mode « previous next »
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Author Topic: Can't Exit Edit Mode  (Read 2290 times)
bsellon
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« Reply #8 on: January 17, 2017, 01:15:37 AM »

I would also run the button test in the diagnostics. Press and hold the Edit button while powering up I believe.

There is also a possibility that the some bad value has gotten into memory somewhere either from a bug or a component failure and is somehow managing to prevent the system from going into the Program select mode.  Because of the Program Chains, Midi Program Maps, etc. the Program mode is not actually that simple in terms of code and could possibly be derailed by some corrupted memory but I was thinking that you might be able to get it to run a full factory initialization by lifting one of the pins on the battery and leaving it overnight. On power up, the G2 is expecting to see a few specific pieces of data at specific locations in the battery backed up RAM to indicate that the initialization has already been done. If the battery is disconnected for a while the data in the RAM gets randomized so the G2 should perform a clean startup. It's also worth looking in the diagnostics in case we put something in there to reinit memory (it's been a while).
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NotASpeckOfCereal
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« Reply #7 on: January 16, 2017, 11:51:20 PM »

Another thing occurred to me as I was re-reading the full post: another possibility is that padding on the plunger for the edit button came off and is stuck on the board causing the button to be permanently pressed.

Thanks Bob.

I got all of that taken apart, made sure none of the soft buttons were permanently pressed or their conductive parts mucked up. Nothing there.

So I ended up shorting the wire grids you speak of. I found that I could actuate every button except for the PROGRAM button.

NOTE: just to be sure it's clear, I started this thread saying that the EDIT button was stuck, but that's not the case. It turns out that I could get into the SYSTEM, STORE, EDIT, and all other buttons except PROGRAM. So the statement "can't get out of EDIT mode" is still mostly true, but only because the PROGRAM button is the faulty one (meaning I can't change patches/programs, so forever in Edit mode).

Also, the KNOB is wonky (this unit took a fall once), so I could use the entire assembly, which is listed as Item 14 on page 8-49 of the service manual. On page 8-51, it's listed as Part #750-11565.

Digikey doesn't seem to have any Lexicon parts (they aren't listed on http://www.digikey.com/en/supplier-centers). The part number doesn't turn up anything.

Should I contact Lexicon through their web site? They seem to want to point me to service centers, which means parts mark-up and labor, perhaps shipping.

I'm not currently employed and this is a plug-in part, so I can do this work myself if the part is affordable enough.

Thanks, Chris
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bsellon
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« Reply #6 on: January 16, 2017, 10:54:48 PM »

Digikey is your best bet for parts though some might only be available through Lexicon.

Another thing occurred to me as I was re-reading the full post: another possibility is that padding on the plunger for the edit button came off and is stuck on the board causing the button to be permanently pressed.

If you look at page 8-43 in the service manual you'll see the schematic page for the front panel. The buttons are set up on a 4 x 5 wire grid where each button shares the wire with others. On the schematic you'll see that the PROGRAM button is on the same wire as the GAIN, EFFECT 1 and  EFFECT 2 buttons vertically (when the page it rotated) and the EDIT, SYSTEM and STORE buttons horizontally. If all of the other buttons are working, then the problem is not a chip.  You should be able to short pin 8 of J2 to the cathode (the side with the line) of the diode D32. If that causes you to get into the Program mode, the problem is the connector or etch leading to and including the switch contacts and that you can probably finagle a replacement momentary button.   

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NotASpeckOfCereal
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« Reply #5 on: January 16, 2017, 06:35:23 PM »

Can someone point out a good path to follow to order the part?

Also, if I can find this part, I might be interested in picking up v1.1 of the system. I'm still on v1.0.

Any contact info is appreciated.
Thanks,
Chris
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« Reply #4 on: January 16, 2017, 06:28:49 PM »

Hi all,

I think I've identified the part I need to replace to get this Lexicon MXP G2 working again.

I have the service manual that I picked up on this site and have ID'd the item and part number.

Can someone point out a good path to follow to order the part?

Thanks for any help,
Chris
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NotASpeckOfCereal
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« Reply #3 on: January 07, 2017, 05:32:02 PM »

Hi Bob, delayed reply.

Thanks for the post. I saved it for when I had time, which was last night.

I took it apart, took off the rubber front with the conductive contacts, and was able to switch buttons back and forth using a screw driver (with a rubber handle to be sure) by touching it across the circuit mesh (what the conductive backing part of each button would normally do).

I conclude that all buttons work including the Edit button, but except the Program button (so 7 of the 8 buttons work, some of them such as the left/right arrows only when in the proper sub-menu of course). I can activate all of the other LEDs with the screwdriver except the program button. I can get into the System menu, find the Init, and reset the entire device back to factory settings, but when done, it goes back to the Edit button, or at least, the Edit button is the only way to exit the System menu.

I suspect that the Program button would exit system, and that it is also the method to leave the Edit menu, but I just can't do it.

I even tried removing the main ROM chip (the v1.0 I think would be replaced were I to get the v1.1 chip) and fire it up, then replacing the ROM chip hoping that this would clear the button state, but it didn't.

So I'm at a loss now at how to fix this device. It's a shame to throw it away. Perhaps replacing that one board behind the buttons?

Chris


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bsellon
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« Reply #2 on: June 24, 2016, 12:12:23 PM »

Hi Chris,
It sounds like the button board got damaged or got some conductive material shaken onto it. The buttons are basically plungers with conductive material on the tips that short a couple of etches when pressed so something conductive might have come loose and is laying across the etches. I've also seen situations where conductive material actually grows across the space between etches but that was in the presence of solder and flux which are not present in G2 button assembly. That doesn't mean that it couldn't happen but is less likely.

I'd recommend carefully taking the front panel apart taking lots of pictures as you go to help you remember how it goes back together and taking a close look at the circuit board behind the rubber button assembly (all the buttons are part of one hunk of rubber). If the spot where the edit button hits looks funky you might try cleaning it with an exacto knife but compare the Edit button plunger to the other buttons. The tip is conductive and may have even came off and got stuck on the circuit board.

At the end of the day, the Edit button is just a momentary (normally open) switch so there are a lot of other options for repairing it if you don't mind an odd-ball switch. You can check to see if it's shorted by using a multimeter to check the resistance (ohms) across the button pins/etches. The resistance should be more than 1K but will be seen as a closed switch if less than a 100 ohms or so.

I hope this helps.
Bob
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NotASpeckOfCereal
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« Reply #1 on: June 02, 2016, 09:02:12 PM »

Hey all,

New poster, old MPX-G2 owner. However, I'm just firing it up after a long period of disuse.

It has been working fine in respect changing patches, but the other day, I hit the Edit button, but now cannot exit the Edit mode

Things I have tried:
1) pressing pretty much any other button. Even if the other button lights up and the Edit button light goes off, when I exit the other button mode, it goes right back to Edit
2) Powering cycling it. When it's done with it's power-on cycle, it comes right back to edit mode.

I can't change patches when it's in this mode, so it renders it mostly useless, except for the patch it's stuck on.

NOTE: the rack this thing used to be in once took a tumble. I had to take the MXP apart to re-seat ribbon cables to get it to work again. Some things still don't work 100%, such as the value knob, which skips values (goes from 1 to 3, skipping 2).

Thanks for any hints.

Chris
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The Stec Records Forum  |  Audio Gear  |  MPX G2  |  Can't Exit Edit Mode « previous next »
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