lcds stay blank

Testing/Troubleshooting
1

hi there!

i’ve managed to get my mbseq working in a shoebox, thanks to the forum and all the docs on here. it was really quite easy! (for someone with no electronics skills whatsoever)

anyway, now the troubles come:

i tested with one 2x40 lcd (the ones from voti.nl) connected, and this worked without any troubles. then i decided to hook up the second one.

after some soldering this also seemed to work, with the only problem being: only one lcd showed text: the other one gave me the black bars on startup and went blank after that (only the backlight stayed on).

hoping it would help any, i decided to fiddle with the (very awkwardly placed, on mikes pcb’s) contrast trimpots. i powered off, turned the pots a little, powered on again and voila: no more lcd’s.

now only the backlight comes on, and i get only the black bars on lcd #2, the one that didn’t work in the first place.

the first lcd just stays entirely blank.

i tried turning the contrast back the other way again, but this doesn’t seem to help any..

i also checked the connections and everything seems to be wired up correctly (i wanted to state 'tidily, but i’d be lying :wink:

read any post that had ‘lcd’ in it and i’m totally lost.. please help!  ???

i’d like to know why i don’t see anything on either lcd anymore, and why the second one only gives me the black bars, since that was the problem in the first place.

thanks a million

2

update:

the problem has changed a bit: i fiddled with the contrast pot some more and now the first lcd is working again.

still leaves my with the fact that the second one only shows me black bars on power up, and nother after that.

is it a software error maybe? i checked the standard config files but it was configged with 2 2x40 lcd’s by default, so i doubt it will be this.

still puzzled.

edit:

some more info: i’ve uploaded mios onto my preburned pic, and uploaded the mbseq application. i can’t measure voltages from the core j15 to the lcd’s since my multimeter is a bit weird. i measured the resistance though, and that was all fine. i doubt it being a voltage error, but on the other hand i have such little knowledge of electronics that i can’t really say anything about it.

edit 2: i notice when pressing certain buttons (i can’t say wich are wich since i have it all just loose in a shoebox) the first screen goes blank.

other buttons seem to work normal though.

edit 3: uploaded midio128 to check out if there is anything wrong with the connected buttons and they all send out a message as they are supposed to do. the only weird thing is that the lcd just goes entirely blank from the beginning here, although i am not sure anymore if this is the way it’s supposed to be.

3

Sounds like a short… might be worth (re)checking solder joints and fixing up that meter?

What happens to the LCD’s if you leave off all those loose switches (or just the whole DIN)?

4

i disconnected the din and the second lcd is still not working.. the button - lcd going blank thing might be something different, since that part did work okay for a while, also with 2 lcd’s connected.

i checked the connections to the PIC for false wiring (easy to make a mistake with all the double wires) but that part seems to be okay.

i have a feeling it might have something to do with the enable line.. gonna check those solder joints..

edit: well, i checked every joint on the lcd, the j15 pins, but they all work. measuring a neat 0 ohms.

i also measured the lcd > j15 connections on the bottom side of the core pcb to be sure that the error wouldn’t be in the connection of the pins to the board, but it all seems to be safe. as far as any soldering errors go: the error must be in the data or enable lines, or else the lcd wouldn’t even show me the black bars, or light up the backlight.

are you sure i don’t need to enable anything in the seq application? did i perhaps upload the wrong hex file (i uploaded setup_mbseq_v2.hex) ?

edit 2: i tried switching the enable lines. this doesn’t help much, apart from that i now see what’s supposed to be on the other screen. apparently nothing wrong there..

edit 3: i think i found a short, but i’m not sure if this is due to my lack of electronics knowledge. it’s between vss and vdd on the j15 pins. i’m wondering if it’s really a short or if it’s supposed to be there, since there is not really any bad soldering in that area, and i can’t get it to go away (i tried screaming, waving crucifixes in it’s direction and finally soldering it again :wink:

any idea? :slight_smile:

edit 4: since the working lcd also has the same problem, in theory it can’t be this short, right? my not-very-reliable meter gives me about 450 ohms between vs en vd.

5

:o :o :o :o :o :o :o :o

i fixed it!

it was ofcourse a typical newbie-thing: yelling really hard that everything is okay while it was just bad wiring: i mixed up Vo and RS on one of the lcd’s.

thanks for the help and sorry for another demonstration of newbie’ism :wink: