Electronics > Beginners
240x64 LCD replacement
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Mp3:

--- Quote from: Twoflower on April 16, 2018, 05:47:50 pm ---You should double check that the tin 20 on your instrument is not connected even if the old LCD does not have anything there that does not mean that the instrument does not use it. If in doubt, un-solder the wire of pin 20 on the instrument side and insulate the end. This allows to make the bridge direct on the PCB of the LCD without the fear that the instrument uses that pin.

--- End quote ---


Excellent idea  :-+ :-+ :-+
Mp3:
Hi everyone,
 sadly i am back to ask for more help.

I've measured the power supply unloaded - seems fine? So i don't think i've destroyed it, yet. I am not sure how to measure it with everything plugged in, since i don't want to damage something else by my ignorance.


Still no power with the new LCD screen. If the charge pump has been damaged already, then it makes sense why it isn't working still, but it's been wired up properly now.

On the power supply, 2 fuses are good (2x 500mA 250V).  1 is blown (1A 250V).  I will replace the fuse, but not sure why it blew.

Unfortunately the screen is the only indication the instrument is getting any power - no power LED or similar....
Twoflower:
As starter you can measure if the LCD gets it supply voltage: Measure between pin 2 (GND) and pin 3 (VDD) of the display. Careful not to make any shorts with the tips of the multimeter. You should measure approx. 5V. If that's correct the keyboard should at least have some parts powered.

Next would be to check if the charge-pump in the display is still working: Measure between pin 2 (GND) and pin 9 (VEE). You should measure roughly -10V. This voltage is probably not very accurate, that's OK. And if completely missing that's a problem as it is required to drive the crystals between the glass plates of the display. As mentioned earlier the display is generating the -10V and is reduced to approx. -8.5V (depending on the contrast setting) using a voltage divider. And feed back to the display at pin 4 (V0). It shouldn't be too low. Otherwise the contrast is low.
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