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CFAG12864B-YYH-N: How to get the negative voltage?

uda

New member
Hi,
I recently bought the above mentioned display - and realized at home, that it has no generator for the negative voltage, which is necessary to be able see a image on the display as I understand.

So, I have four questions:
1 - is it right, that the neg. voltage is (absolutely) necessary to see the display content?
2 - is the space named U4, C1, C2 left blank for the neg. Voltage generator?
3 - is the Max ICL7660 or compatible, combined with two 10µF caps the right choice? In other words: is there a part list or something available for this display, so I can add the missing parts by myself?
4 - is it possible to use the -12V/5V/GND from the standard ATX power supply of the computer instead?

Thx in advance,
uda.

I apologize for my english, as you may have noticed, I'm no native speaker ;-)
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1. Yes, you probably need negative voltage to get enough contrast. On my display, the Vo for best contrast is about -2.7v (Vlcd = 7.7v), for a CFAG12864B-TMI-V. I cannot say what is best for the B-YYH.

2. Yes.

3. Yes. On my display, C1 & C2 are 4.7uF. Also, there are some 0 ohm jumper resistors that do not appear on the board without the Vee circuit parts. I don't know exactly which jumpers do what. I could post a high resolution photo of the back of the B-TMI-V if you think it would help.

4. Yes, but you must be very careful with the -12v supply, as the absolute maximum voltage for Vlcd is -11.7v (with a +5v Vdd). The current requirement for Vlcd is very low, so you could try testing using a 9v battery as negative supply, to determine the best voltage for Vo.
 

uda

New member
Thanks cosmic,

I would appreciate it very much, if you post a highres picture of the pcb.
If the negative voltage generator only consists of the three parts (7660, two caps) then it's easier to solder them on the board; if there are more parts I think it's better to try the solution with the computer's power supply. Do you know, if those three components are all it requires?
 
The 7660 circuit only requires the three parts, but the 0 ohm jumpers at R10 and Q1 (and maybe others) seem to be connected to the Vee node, so they may be required to route the negative voltage around on the board. Without a schematic, I can not be sure. I think adding the 7660, and possibly a few jumpers, is preferable to using a double supply.
 

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uda

New member
Hi cosmic,
thanx a lot for the highres-picture. With this help even I should be able to add the negative voltage generator. I found no differences between your pcb and mine except for the U4, C1, C2, and the jumpers at R10, JE and Q1. Interesting fact - I followed the way of Vee on the pcb and I think, you're right: The 0 ohm resistors/jumpers are necessary to route the voltage... Perhaps I can buy the 7660 tomorrow and use the display in the evening already ;-) Again: Thank you!
 

uda

New member
Problem solved!

Thanks to the help of Cosmic, I was able to solve the problem with the negative voltage generator.
The only parts I needed were the two caps (4.7 µF) and two 0 Ohm resistors - and the display is working fine... :)
thanks for your help!
 
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