LCD display issues

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Rob Flinn

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I have a Lexicon MRC which has a slightly flakey LCD display in that it's quite faint and not really readable unless you are at exactly the right angle.  The contrast wheel does nothing to help.  I bought a compatible display to replace the exisiting one but have a weird issue.  What happens is that the display starts showing random weird characters over the top of the wanted data.  If I then move a slider or press a button on the MRC the display goes back to normal then again slowly starts displaying random characters, so that the wanted data is completely eventually covered and unreadable until I move a slider etc again.      If I reinstall the original display this doesn't happen, so it must be some sort of glitch with the new display.  Any ideas ?
 

nashkato

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i´m about to do the same once the new display finally arrives  .
MRC have an EL-Panel as backlight , i assume you removed the HV from the old EL backlight ?
 

Rob Flinn

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nashkato said:
i´m about to do the same once the new display finally arrives  .
MRC have an EL-Panel as backlight , i assume you removed the HV from the old EL backlight ?

Yes, I removed the step up transformer thing.
 

radardoug

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Well, sounds like the select line to the display is flaky, so stuff on the micro bus is being loaded in when it shouldn't be.
 

Rob Flinn

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radardoug said:
Well, sounds like the select line to the display is flaky, so stuff on the micro bus is being loaded in when it shouldn't be.

Thanks for the tip Doug I will look at the select line.    Is it likely that the new display is loading the bus more than the old display that doesn't display this behaviour ?
 

radardoug

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It could  be a threshold or timing issue. Look at the pin with a scope. You might find loading the pin a bit will fix the problem.
 

Rob Flinn

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It appears the issue was on the display itself.  I swapped it out with a different new display & it's working fine now.

Nashkato it's quite an easy job.  Take the display ou,t buy a new led cheapo 2 x 24 display on ebay or wherever.  On the new display the header is a 2x8, on the old one it's 2x7.  On the new display you only need pins 1-14, so just don't put the header into positions 15 & 16.    The ribbon cable fits in the same orientation as on the old didsplay.

Make sure you by a 5v display.  Then you can pull out the black invertor transformer for the back light off the main board.  I installed a resistor (to lower the current a bit) as a jumper across 2 of the pins where the invertor went so the 5v was connected through to the original 2 pin header for the display power which has black wires going into it.  The other end of the black wires is soldered onto the A & K pins of the display at the other end to the main header.  If it doesn't work the reverse the polarity of the 2 pin header.

The other main thing is that the 2 metal u shaped mounts screwed to either end of the display have to be mounted on the front of the new display as opposed to the back of the old display.  This is because the new led displays are thicker than the old EL backlit display & you need to jack the new display away from the window to accomodate it.

 
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