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Lexicon MPX-1 Wont Boot
Old 16th March 2017
  #1
Here for the gear
 
Lexicon MPX-1 Wont Boot

I have a Lexicon MPX-1 that is dying on boot up.

When first powered on, all the LEDS light up and then it begins the boot process where the peak LEDS start to count up. It gets to the place in the boot process where the main display should come up but the display remains blank and none of the LEDs are lit.

I have the service manual and schematics and have been looking into what may be the issue.

I tried the entering the extended diagnostics but the unit just starts going through the boot process and then dies.

I also tried the emergency diagnostics and was able to select the "Initialize Operating System" but when I execute it again the unit just goes blank. Not sure what the LCD Write/Read Scope loops are as the manual does not explain their use.

I did some initial trouble shooting using the service manual and all the voltages are within tolerance, all the clocks are also good and within tolerance and the battery is at 3v.

Looking at the reset lines, it looks like the unit is hanging right after the reset line for the Lexichip goes high (unreset). It appears that this is where it is hanging up. It never gets past this point so the DSP reset line is staying set (low).

Looking at signals on the scope I can see that there are reads happening between the Z80 processor and the Lexichip.

At this point I am not sure what the issue could be as I am not sure exactly what self test is running. Possibly the Lexichip itself or perhaps its associated the DRAM.

Has anyone run into a similar issue and if so could provide any points on where to look?

Any help would be most appreciated.

Thanks, Dan
Old 26th March 2017
  #2
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MPX-1 Binaries

So after a lot of trouble shooting I narrowed the issue down to a bad EPROM.

Unfortunately I don't have an image to burn a new one.

Anybody have a MPX-1 ver 1.1 image or EPROM that I could acquire?

I am trying to get one from Lexicon/Harmon but it is not looking good.
Old 30th March 2021
  #3
Here for the gear
 
Did you figure it out? I’ve got the same exact problem and trying to find out what can cause it before I buy new power supply or eprom.
Old 30th March 2021
  #4
Here for the gear
 
Did you figure it out? I’ve got the same exact problem and trying to find out what can cause it before I buy new power supply or eprom.
Old 31st March 2021 | Show parent
  #5
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Quote:
Originally Posted by AdrianM55 ➡️
Did you figure it out? I’ve got the same exact problem and trying to find out what can cause it before I buy new power supply or eprom.
Yes I did figure it out.

It was not the PROM as I originally thought but the display.

I found that part of the startup routine writes and then reads back from the display. This is part of the self test at startup.

If the display is bad the code just sits and waits for it to respond and if it does not then it hangs. Once I replaced the display it booted right up.

I also used a cheap LCD display versus the very expensive one that is in the unit. The one I used was the following although any that are similar should work OK.

https://www.ebay.com/itm/1602-16x2-H...wAAOSwKiZfHeMy

I also purchased this one as a backup but have not tried it yet but my guess is that it will work fine.

https://www.futurlec.com/LED/LCD16X2BL.shtml

If by chance that you need the EPROM code I have that also. You can use that to burn a new EPROM if needed.
Old 1st April 2021 | Show parent
  #6
Here for the gear
 
Thank you very much for your great answer mate.


https://www.dropbox.com/s/w9q3pvdl3r...%2028.mov?dl=0

Before I order this display could you please watch this clip from Dropbox to confirm you had similar problem?
Sometimes I can switch to 2 and press store but then displays goes blank and comes back to squares again.
Only once I managed to to get “d” for reset but couldn’t progress.
Old 1st April 2021 | Show parent
  #7
Here for the gear
 
Quote:
Originally Posted by danjp ➡️
Yes I did figure it out.

It was not the PROM as I originally thought but the display.

I found that part of the startup routine writes and then reads back from the display. This is part of the self test at startup.

If the display is bad the code just sits and waits for it to respond and if it does not then it hangs. Once I replaced the display it booted right up.

I also used a cheap LCD display versus the very expensive one that is in the unit. The one I used was the following although any that are similar should work OK.

https://www.ebay.com/itm/1602-16x2-H...wAAOSwKiZfHeMy

I also purchased this one as a backup but have not tried it yet but my guess is that it will work fine.

https://www.futurlec.com/LED/LCD16X2BL.shtml

If by chance that you need the EPROM code I have that also. You can use that to burn a new EPROM if needed.
What programmer do you use? Also I don’t really know what chips where used to be honest.
I assume it’s FW1.10?
Send it over to my mail if you could please [email protected]
I hope it works.
Old 2nd April 2021 | Show parent
  #8
Here for the gear
 
That looks very similar to what mine was doing. Not exactly the same but very close.

What tripped me up for a while was every once in a while it would almost boot then die.

I finally put a logic analyzer on the display bus and could see where it would write the data and then freeze when it tried to read it back out.

My guess from looking at your video is that it is the same issue.

I will email you the code.

I used one of the universal programmer TL866 II Plus.

https://www.ebay.com/itm/XGecu-TL866...S/223495002463

There are a ton of them out there. The big difference between them is the adapters they sell. So the best bet is to get one with all the adapters you need. Getting them after the fact will cost more than just getting one with everything.
Old 2nd April 2021 | Show parent
  #9
Here for the gear
 
I should also tell you that the power supply is prone to going bad also.

I bought a second unit that had a bad power supply in it.
Here is a link to the replacement supply. They are fairly cheap and not worth repairing.

https://www.trcelectronics.com/View/...l/PT-45C.shtml
Old 2nd April 2021 | Show parent
  #10
Here for the gear
 
Thanks Dan! Very informative and well put down. I will order that power supply as a spare as their price is fair and doesn’t break the bank.

Looking for programers and they’re holding the price. Need to think if I need all of these adapters tbh.
I’ll keep in touch with you . Thanks again
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