VFD problems

J

JEEVES/whohasmyname?

Gawd
Joined
Mar 25, 2004
Messages
696
Ok I have been stumped :confused: . I have a noritake 64x128 graphic VFD. Wired it up correctly and had it working perfectly. Then I put it into my new case with new mobo and proc and the damn thing goes haywire. It looks like there is alot of interfearence or crossed data in the lines. You can see the image but it breaks apart and jumps all around (it is real hard to explain). basicly it looks kinda like static on tv but not as small of "snow". I hope you understand what i am trying to say.

Now first thing i did was rewire the thing, tested it on old computer and works great hook back up to new pc and same thing. now I do have "lightning" tubes on new pc (see project black lightning for more details), so i was thinking mabey they are putting off an emp or something. disconnected them and hooked vfd up to diffrent powersupply and still get same thing. Wich cuased me to think well it must be my lpt1 port. So I made sure everything was the same on the two pcs, even the irq numbers. They were and still get same thing. Uninstalled the lpt1 drivers and reinstalled, same thing. Uninstalled the port i/o drivers as well as lcdstudio and reinstalled them (from new downloads), same thing. I have run out of ideas, what on earth could be cuasing this? I am about ready to say that it must be the lpt1 port, but not sure what i can do to fix it.

So i turn to the forums for help, please if anyone has any ideas let me know.

JEEVES

edit* here is the data sheet for the vfd http://icehw.net/article/graphic_vfd/noritake800.pdf
 
well... If te ligtning tubes, as you call them, use an actual free electrical discharge, tat's whats screweing up yur VFD. I had this with a TV and one of them plasma discs (the borg alcove things), and since TVs and VFDs operate by the same principals...
 
Little Grabbi said:
well... If te ligtning tubes, as you call them, use an actual free electrical discharge, tat's whats screweing up yur VFD. I had this with a TV and one of them plasma discs (the borg alcove things), and since TVs and VFDs operate by the same principals...
Click to expand...


even when there is no power to the tubes? if there is no power to the tubes then they shouldnt put off any sort of emp. So why would it still be cuasing a problem.

JEEVES
 
I've heard that sometimes a sagging power supply can cause problems. But if you've reduced the load and you're still having problems chances are that's not part of the problem. Have you tried wiring it up outside your case with all the side panels on, so you don't get any EMI ( I assume the case is at least mostly intact).

The other possibility I can think of is the voltage levels coming from the parallel port may not be what they need to be. I don't know if that VFD is actually powered by the parallel port, but if it is, that could be the problem. I've heard that the 5V that should be there isn't always exactly 5V, especially if a lot of current is being drawn from that pin. Try taking 5V from a molex connector and see if that helps.
 
Teancum said:
I've heard that sometimes a sagging power supply can cause problems. But if you've reduced the load and you're still having problems chances are that's not part of the problem. Have you tried wiring it up outside your case with all the side panels on, so you don't get any EMI ( I assume the case is at least mostly intact).

The other possibility I can think of is the voltage levels coming from the parallel port may not be what they need to be. I don't know if that VFD is actually powered by the parallel port, but if it is, that could be the problem. I've heard that the 5V that should be there isn't always exactly 5V, especially if a lot of current is being drawn from that pin. Try taking 5V from a molex connector and see if that helps.
Click to expand...

I have tested it on a diffrent powersupply. It is drawing its power from 5volt molex. But it does still use the lpt1 for some current. I have tested it outside the case with all the sides put on (project Black Lightning). I am going to be trying a few other ideas tonight, will let everyone know if it works or not. thanks for the help

JEEVES
 
i am thinking that the newer motherboard doesnt follow the LP standerd as exactly as the older one did. try making a buffer that eliminates the current draw from the printer port using 8 or 9 transistors.
 
That's a pretty good suggestion. If the signal corruption is not being caused by some power supply glitch, a buffer stage for the LCD might be worth a try. Or, if you have access to a logic analyzer or oscilloscope, you could check your output to the VFD to see if the signal itself is sagging. Also, shotgun debugging can sometimes be helpful. What's different between your two pc's?

motherboard
software

You've done everything I would have thought to do with software, so it could be your MB. If you could test the signal coming out of the motherboards, you could potentially compare the two for differences in signal level.

I don't know enough about parallel ports to avoi sounding like a noob(after this semester, that'll be different!), but would changing the parallel port mode work (standard/EPP/whatever)?
 
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