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LCD problem, help?

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I've gotten through construction of the base PCB, and partially through the control PCB, specifically the part with the LCD screen. When I plug it in, I get nothing from the screen when the unit powers up. I've loaded the bootloader onto a PIC, along with MIOS over midi, and the setup_MB6582 hex. So I am expecting to see something on the screen, but not even a backlight. 
The screen is a Midas MC42005A12W-VNMLR, a HD44780 equivalent, and I've checked the pinout and its the same configuration as in Hawkeye's tutorial. Can anyone help me trouble shoot this? Is it possible that I would need to bridge the jumper pads for 8bit operation? R80 is installed. I'm fairly certain the bootloader/mios/FW installed correctly. I have not yet inserted any SID chips yet. Is there any way that I can test if the screen is defective? I've popped the PIC out of core_1, and dropped in into 2, and still nothing from the screen. Only difference that I noticed, is that core_1 has a constant ~5v coming out of pin 9 on j15_core1, while I didnt see that on the other cores. I've tried adjusting P1, and P2_core1, etc. and no difference there either. 

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I've tried the LCD test app with MIOS, and all seem to react ok, except D0 doesn't seem to react on the PIC leg. I've measured the voltages across the pads on the LCD, and D7-10 have a constant ~5v. B+/j15_core1 pin9 is also at a constant 5v too. Are these readings normal? Do I just have a dead screen?

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On 8.3.2020 at 0:13 AM, njosnari said:

but not even a backlight. 

If you don't even have a backlight than it is difficult to see something.

Mostly the last Pins at the Display are for Backlight, you can put 5v and - at the pins and backlight should work. If not so, it's dead.

Than you have those trimmers for Backlight and Contrast, have you turned them?

Maybe you need a negative Voltage for the BL, this is often the case but I don't know.

Edited by Noise-Generator
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22 hours ago, njosnari said:

Would that be it tho? #9 on the next page lists the supply voltage for the backlight at 5v. So I should still be able to see the backlight?

I'm not sure. 

Look at the page you linked to, there is a rating of 5.5v.

By google-ing MC42005A12W I found two pages where supply voltage is = 6,5v


and you could read this thread:


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Here they fixed the same problem by bridging PIN3 and PIN15 with a 9.8k resistor.
Since i bought the same MIDAS dysplay please report if that works, would be usefull when i will build my own.
Thanks, hope it works!

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Pin15 (Vee) on the Midas display is a negative voltage OUTPUT! So do not connect this pin to your Midibox PCB. Instead connect it like in the circuit from the data sheet with a 10k-20k trimmer to Pin3 (Vo) and Pin2 (Vdd). In this case Pin3 also must not be connected to your Midibox PCB.


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Hey everyone, problem solved!


I followed the instructions in the link, and by removing pin 15 and 3, and shorting them with a 10k resistor did the trick. Also, turns out that this screen takes - power, so I had to swap pin 15 and 16 around. But so far this screen does seem to work!

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