[sdiy] LCD hot rodding

mark verbos markverbos at gmail.com
Mon Apr 8 16:35:34 CEST 2024

> On Apr 8, 2024, at 3:29 PM, Roman Sowa <modular at go2.pl> wrote:
> I wouldn't want to sound rude, but if something works, even barely, like one row display, that's a good sign that power polarity is correct and reversing it then is like sticking a fork in power outlet.

So it seems. 

> Your OLED replacement was't probably fully 44780 compatible, or it was the other way - original one was some kind of freaky one, not compatible with 44780. I'd try any cheap LCD now to see what is still working.

It still works with the original, just without backlight. 

> About solid black boxes - are they in one or two lines? If there is only one line of black boxes, it may mean it just got power and nothing else plus very miss-set contrast. If you see 2 lines, it means that some config codes were succesfully written to the display so at least the LCD controller IC is working.

One row. Controlling the contrast just dimmed the black boxes. Looking at the data lines, everything looks pretty curved on the rise. In the schematic, I notice that each line going to the display has a 10k pull up and a 10k pull down. Could this be the problem?


> Test every signal of the display, at the display, during powerup: data bits, RS, E, to see if there is activity. One of those signals might be simply broken.
> Roman
> W dniu 2024-04-08 o 14:38, mark verbos via Synth-diy pisze:
>> I have a Linn 9000 on which I’d like to replace the display. It is a 16x2 EL backlit one. I bought an OLED one and an LED lighted one from Mouser. Inspired by what Forat does, I got bigger ones. The original display uses a 14 pin, dual row connector.
>> First I plugged in the OLED one it looked great, but only the top row displayed. Checking my work, I noticed that I had the power pins reversed, according to the document I was referencing. I switched them and now the display is dead. It turns out the document I was looking at for a 14 pin connector on a LCD display was wrong  and I had gotten lucky having them the right way to start. All the other wires buzzed out ok, I’m afraid to buy another display, unless someone tells me it’s possible to get it working.
>> Second, I plugged in the LED backlighted one today. The backlighting looks great, but I only get solid black boxes all the way across the screen.
>> Does anyone know about these things? What am I doing wrong here?
>> Mark
>> PS. The Linn’s power supply was already melted down when I got it. I brought that back to life. This thing has the Forat sampling mods, which is a rat’s nest. I have software 7.01 (7.09 is the latest). Emails to Forat bounced. Is he still in business?
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