Help with LCD change on my synth

Thread Starter

hide24

Joined Jul 9, 2019
36
Hello everyone,
I bought a new VFD 1602 (7pin, 14 in total) for my synth but I can't make it work correctly. Although I connected all the pins in their place, I only see the characters randomly .

The original synth's LCD is 1602 (8pin, 16 in total) and behind it had one cable soldered that goes from it to the electronic board ( not sure if its a ground wire)

The curious thing is that, to see my VDF with the correct characters, I tried putting that "ground cable" over of the different pins until for my surprise something happened. The display worked fine!!
When I connected the wire to the pin 2 and turn ON the synth, nothing happened, but when I released it , the display became totally fine!
Like a on/off switch. But if I solder, is like being OFF again.

What am I doing wrong?

Thank you very much for the help and sorry of my english, I'm not native speaker.
I recorded a video where you can see , and upload pictures of the datasheet of the LCD and VFD.

Here's the link:
 

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Brevor

Joined Apr 9, 2011
297
Can you post pictures of your unit. A closeup of how you connected your wiring.
 

Ian Rogers

Joined Dec 12, 2012
647
As you seem to have used the same connector, pin 3 ( vo) isn't a logic anything, so the reset isn't "low"... Pull pin 3 low (gnd )
 

MrChips

Joined Oct 2, 2009
19,160
What you are doing is momentarily shorting the power supply.
This has the effect of performing a power on restart.

When the power is turned on for the first time, the computer sends initialization commands to the display.
All displays need this initialization procedure in order to perform properly thereafter.
 

Thread Starter

hide24

Joined Jul 9, 2019
36
Thanks Mr.Chips,
So, the problem it's on the initialization? it's just when appears all the characters randomly, but when I do the short circuit, seems show them correctly.
 

MrChips

Joined Oct 2, 2009
19,160
Pin-3 is normally contrast control.

You need to break the connection driving pin-3 and wire a 10kΩ resistor from pin-2 to pin-3 on the new display.
 

Thread Starter

hide24

Joined Jul 9, 2019
36
Thanks !
So it means, remove 2 pin, (the number 2 and 3) and from there, solder a resistor of 10kΩ, isn't correct?
 
Last edited:

MrChips

Joined Oct 2, 2009
19,160
Try it first without the resistor.
If you have a voltmeter, measure the voltage at pin-3 with respect to GND, pin-1.
 

djsfantasi

Joined Apr 11, 2010
5,477
Thanks !
So it means, remove 2 pin, (the number 2 and 3) and from there, solder a resistor of 10kΩ, isn't correct?
What do you mean by “remove pin 2”? Don’t change pin 2. Add one end of a resistor (10kΩ) to pin 2.

Disconnect pin 3 from anything it is connected to (it may not be connected to anything). Connect the other end of the 10kΩ resistor to pin 4.
 

Ian Rogers

Joined Dec 12, 2012
647
You are all correct!! Active low... LOL Yes! Pull the pin high!!

10k to pin 2 will do it!
 

Wolframore

Joined Jan 21, 2019
1,168
Pin 3 doesnt matter...

internal pull up on RST, RS, RW and E

RST active on LOW

upload_2019-7-9_10-47-12.png

JP1 not bridged
upload_2019-7-9_10-46-23.png

upload_2019-7-9_10-45-59.png
 

Thread Starter

hide24

Joined Jul 9, 2019
36
Just right now I removed the pin 2 and 3 from the new VDF but seems not turn on the display.
I'll try djsfantasi now..and see if it works!
Thanks everyone :)
 

Thread Starter

hide24

Joined Jul 9, 2019
36
Wolframore Thanks,
I'm very new with this. You mean I should keep the pin 3 without remove it?

"internal pull up on RST, RS, RW and E
,RST active on LOW"

What does it mean?
 

djsfantasi

Joined Apr 11, 2010
5,477
Just right now I removed the pin 2 and 3 from the new VDF but seems not turn on the display.
I'll try djsfantasi now..and see if it works!
Thanks everyone :)
DONT!

I made a typo. Connect the other end to pin 1... (not 4)
 

MrChips

Joined Oct 2, 2009
19,160
TS, you have it wrong. Go back and read the instructions carefully.

Do nothing to pin-1 and pin-2.

Your issue is with pin-3.
Read post #14.
If there is a jumper described as JP1, remove jumper.
That should do it.

Edit: According to your photos, JP1 is not bridged. Hence it should work as is.
You are back to square one.
 

Thread Starter

hide24

Joined Jul 9, 2019
36
Yes, I tried pin1 and pin2 with resistor but didn't work.

Jumpers there are not. Only the pins. I only removed pin 3 .
When I bought the display it was nothing installed on it.
Anyway, in case there were jumpers it would be impossible to connect then the pins, isn't it?
 

MrChips

Joined Oct 2, 2009
19,160
As I said, you are back to square one. The display should have worked as is straight out of the box.

After connecting the display, did you turn all power off and on again?
 
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