I am a new member to this group and I wanted to share a conversation I am having with Mr. Bob Sellon regarding the subject start up problem I am having with my MPX G2. Please read our correspondence to date starting at the bottom of this entry and add your comments / recommendations as you see fit.
I'd like to thank Bob again for all his help thus far and I look forward to sharing my experiences and ultimate resolution of this issue with this group!
You didn't mention reverb. Is the reverb also not working? Reverb and delay are both done by the Lexichip.
A bad Lexichip is certainly a possibility but I haven't had a lot of experience with chips becoming intermittent. Once they develop a problem that's usually it but it's possible that the chip itself is coming apart. You can sometimes localize a problem by using a heat gun and freeze spray. I would sometimes use the cardboard center of a roll of toilet paper to keep the heat or cold on a single chip while listening to a simple "bong" or other pure tone on the reverb to see if I could hear a change when a particular part of the circuit was sensitive. When chips fail, they will sometimes change as they change temperature.
If you can, it might be worth trying to reflow the solder on just those pins with a fine-tip soldering iron. If there is bad solder, the pressure of the multimeter probe will make it work while you are doing your test. You could also set up a reverb or delay program and see if it cuts in/out when you press on those pins or the chips.
I hope you don't mind but I'm going to put this discussion on our forum so others can benefit from it.
Thank you again for your reply. I checked the pins/circuits below and I have continuity between the two chips at the leads. Off the top can you think of anything else I can check? Are there other pins that handle serial communication between the two chips? Is it possible that my Lex chip is bad? As I indicated before the unit works well except for delay functions.
Thanks for your help,
You are on the right track inspecting and trying to reflow solder. My buddy Keith at TheJukeYard.com repairs a lot of G2s and he's mentioned problems with solder, especially with the Lexichip (U85). I'm pretty sure he has a special tool for his soldering station for reflowing large chips but a heat gun might do the job. Definitely want to be careful not to overheat the chips or the board which can create whole new classes of problems.
I'm pretty sure the Lex-2186 test checks the serial communications between the Lexichip which handles reverb and delays, and the Analog Devices 2186 DSP chip which handles all the other audio processing. Pin 61 is the output and pin 63 is the input on the Lexichip and pin 31 and 34 are the out and ins respectively on the 2186 (U88). Take a close look at these pins but you can also put an ohm meter between them to see if there is continuity and even add a tiny wire to connect the pins manually if there is an open you can't see (crack in the etch under the chip, etc.).
I hope this helps,
Sorry Bob.. I neglected to mention below that I ran all the other built in diagnostic tests (i.e. DRAM, WCS, SRAM, ROM Checksum, Digipot, Sample Rate etc.) and everything checks out OK. The only error I am getting is the Lex-2186.
I have been doing a lot of research on the web with regards to an issue I am having with my Lexicon MPX G2 unit and I see you are a well-known and well respected authority on this subject. I was wondering if you could provide a little guidance. During start up I encounter a LEX-2186 failure. This started as an intermittent problem but is now a consistent issue. When I push the “program” button after this error is encountered the unit starts up and is fully functional except for delay functions. I have read the MPX G2 service manual and have not been able to resolve this issue. I have inspected the board visually for poor connections / solder joints and have found none. I have even tried to reflow the board in the area of the Lex and 2186 chips using a heat gun but still no resolution. I am reaching out to you as a last resort to determine if there is anything further I should try to resolve this problem.
Thank you very much in advance for any help you can provide and I apologize if I am disturbing you in any way by sending this e mail.