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240x64 LCD replacement
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Mp3:
Hi everyone, I have a new question about replacing an old LCD.

I have a replacement for a Toshiba T6963C 240x64 screen. It still works but is very dim and difficult to read. I have two questions

i was following this guide: http://wp.visuanetics.nl/kawai-k5-display-upgrade-cleaning/ and bought one of these displays (product page)


First question
So that guide the guy replaced his with another display that has 20 pins like the stock LCD. My display has 22 pins though. I tied font select to VCC as the guide says. Checking the pinouts everything matches up. Pin 21 is backlight +5v, pin 22 is backlight negative 0v. Currently neither pin 21 or 22 are hooked up. After checking all my connections and continuities, i plugged it in and turned it on, nothing happened, so i unplugged it right away.   I am not sure if i should have expected to see the display work but without any backlight, or if the nothing happens when the backlight is not connected. Right now i am just hoping nothing is broken.

Second question
Pins 1 and 2 are ground.
Pin 3 is VCC +5v.
Pin 20 is negative voltage supply 0v.
Would i be correct to assume pin 21 (backlight +5v) connects to pin 3, and pin 22 "Backlight cathode 0v" connects to pin 20? or do i connect it to ground?


Lastly, Is there any chance anything is permanently damaged?
Twoflower:
The 20Pin displays seem to have a slightly different pinout: http://www.newhavendisplay.com/specs/NHD-24064CZ-NSW-BBW.pdf. The only differences I see are:
Pin#  20Pin  22Pin
9     VEE    NC
20    LED+   VEE
21    -      LED_A
22    -      LED_K
As you connected the pin 20 to the supply voltage for the LED (probably +5V) and the new display provides there a negative supply voltage of about -8.5V there might a chance that the charge pump got damaged. But I don't think your instrument got damaged. Usually the charge pump provides only very little current compared to the +5V.
Mp3:

--- Quote from: Twoflower on April 15, 2018, 10:07:27 am ---The 20Pin displays seem to have a slightly different pinout: http://www.newhavendisplay.com/specs/NHD-24064CZ-NSW-BBW.pdf. The only differences I see are:
Pin#  20Pin  22Pin
9     VEE    NC
20    LED+   VEE
21    -      LED_A
22    -      LED_K
As you connected the pin 20 to the supply voltage for the LED (probably +5V) and the new display provides there a negative supply voltage of about -8.5V there might a chance that the charge pump got damaged. But I don't think your instrument got damaged. Usually the charge pump provides only very little current compared to the +5V.

--- End quote ---

Thank you and sorry for my follow up question but is the charge pump built into the display or the power board?

I also ended up finding the datasheet for the display i replaced. (i think) https://cdn.sos.sk/productdata/ef/bd/dc8ae086/bg-24064a-yplhnt-1.pdf

A problem i noticed:
New display                                                    Old display
9. Not Connected                                                9. Vee Negative Voltage output -13.6 V (like the Newhaven you found)
20 Negative voltage supply                                  20. N.C No connection                                         

So perhaps, i didn't send negative voltage to the wrong place, i sent it to..... no place?  :phew:

Would it be safe to tie pin 9 to pin 20 or is that not advisable? The way the wires are soldered in, it might not be very easy to swap where wires 9 and 20 are, but i will do it if it's the right way to do things.


Another graphic of a compatible pin-out:
Twoflower:
The charge pump is located on the LDCisplay driver.

In case your information is right, then you might be lucky and everything is fine.

With a bridge 9<->20 I would be careful. Either check that the pin 20 is in fact going nowhere on the PCB or measure it: Remove the LDC, power on the instrument and measure GND-Pin20 if there is no voltage present.

And be careful with the not loaded inverter for the EL-Foil of the old display. If no EL-Foil is connected it might generate an extreme high voltage probably not deadly but very unpleasant. Also running it unloaded the voltage is that high that it could kill the inverter. See if you can disable it. It is part of your instrument to prevent some side effects (noise in the audio signal). At least add a good insulation to the leads and fix them at a position that doesn't come close to other electrical conductive parts.

Edit: Added 'could' as the inverter must not get broken but could get broken.
Mp3:

--- Quote from: Twoflower on April 15, 2018, 06:29:41 pm --- If no EL-Foil is connected it might generate an extreme high voltage probably not deadly but very unpleasant. Also running it unloaded the voltage is that high that it could kill the inverter. See if you can disable it.

Edit: Added 'could' as the inverter must not get broken but could get broken.

--- End quote ---

Many thanks again Twoflower!!!

My idea was to remove the high voltage inverter, replace with a 100 ohm resistor, but i thought i should test if everything works before i go to remove it. But, i will remove the inverter and replace with a resistor next time i open the instrument up.  :-+    I have some 5 watt 100 ohm resistors, i hope those are okay?

And many thanks for the advice about bridging pins 9 <-> 20, i will check before attempting to tie them together  :-+
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