Korg Zero 8 Mixer and DIY replacement touchscreen, where to start?

[damien]

Hi dear DIYers,
I own a Korg Zero8 digital mixer which is quite a powerful and unique product.
It was an attempt from Korg to offer an affordable DJ mixer with an internal firewire soundcard, paired with an audio/midi mixer with selectable type EQs, 2 external AUX for FX and an integrated Kaos Pad style touchscreen.
It's great really! I'm still using it a lot to mix with NI Traktor, but the touchscreen digitizer have been faulty on those units from the get go. And Korg dismissed them without any upgrade or fixup solution. They fry like disposable media.
I bought the last 2 touch screen, but they hold like 3-6 months even with a good cooling fan next to it. Not sure why they fail. I replaced them already 5 times.
I think I'm done with this joke, it's frustrating and since there's no longer replacement parts, I was thinking about replacing the whole screen+touch-pannel assembly with a modern LCD solution of the same size and that would be easily compatible. I have the service manual available. Download Korg ZERO8 Service Manual | ManualsLib

I don't know where to start with this because I have absolutely zero knowledge about LCD screens, controllers and everything related to touch-screens in general but I have great skills in electronic and software dvpt.
Can someone please help me with documentations, blog articles, or even upgrades tutorials about this subject but for other devices? That would be awesome really!




Thanks for your help in advance
Damien

 

[Bo Deadly]

It is unlikely that you'll find a display that will drop-in replace. The firmware is going to be emitting precisely what that specific display needs. One would have to use a logic analyzer to see what's on those 8 data lines and try to decipher what it's doing. Someone fluent with LCD communication could probably decipher it pretty easily and might even recognize a similar panel. But chances are it just won't be quite right. There would be some timing that's off, some line that's supposed to go high when something else is low or some such. You would have to "bit-bang" it by decoding it with a separate microcontroller and then transliterate for a new display that you know how to drive. That would require non-trivial code. And of course it won't fit physically.

 

[damien]

Thanks Bo for your reply! this is what I thought, there would be some serious translation involved to fit another LCD to this device. I would need to sample the signals with my osciloscope and try to understand the way it syncs up with the controller/display but since I don't have any references I can't relate to any other LCD available that could do the job. Concerning the replacement screen I could eventually mount it externally if ever the size don't match perfectly. The culprit is the digitizer and it's a custom one just for this Korg. I don't see a bright future for this great mixer unfortunately unless someone knows this kind of thing very well. Have a nice week

 

[Khron]

Looks quite a lot like a resistive touchscreen to me. It's not advertised as "multitouch", is it?

Might be interesting to know what it is that fails on them - do the resistive tracks go open-circuit? If that's the case, and the crack happens to be visible, you might be able to patch it up with some conductive ink, at least as a temporary solution.

Of course, ideally you'd want to get a resistance reading off a working unit first, "just in case", but sourcing a resistive touchscreen might not be as impossible as it might first seem.

 

[damien]

Hi Khron, nope it's not multitouch. It's one of those soft overlay sitting on B&W early 2010s LCDs. Everybody having the same issue with this mixer accused the heat of killing the digitizer. The display is sitting just above the PSU. I added a fan but it still failed over time. I'll check if the tracks test OL on a fried digitizer and will read the resistance on a new working one tomorrow and will update here. it really has something to do with the digitizer because once replaced, the display assembly worked like a charm until...
Do you know if heat from the LCD below or the PSU can damage the digitzer over and over?
I will keep you updated guys. Thanks for your help I really appreciate it.

 

[Khron]

Heat from the LCD maybe; from the PSU, no idea where it's located on the inside, relative to the LCD.

Where did you add the fan, by the way?

 

[damien]

The LCD is located just 1cm above the PSU and I added a fan on one side of the psu to create a nice airflow to bring heat to the outside. I got my last digitizer working for a year which is impressive for this mixer, but it ended up failing as well. I thought about relocating the PSU in an external enclosure that would be the best if the problem is really coming from over heating. But maybe it's just a commmon defect happening to this particular part over time IDK. I'll check the resistance of the touch panel tomorrow and will share it here.

 

[Bo Deadly]

Is the failing part the touchscreen overlay or the LCD or both? If it's just the touchscreen and the LCD is perfectly fine, that is a MUCH easier problem to solve.

 

[damien]

The touch screen overlay is failing not the LCD.

 

[Bo Deadly]

It looks like almost all touch screen overlays are 4 pins and no active components. So it's very likely that they all work the same way. If you can just find one that's the right size there's a good chance that it will work. It might even have the same FPC connector and pinout but even if it doesn't you can probably hack it with a little bit of delicate work on the connector. But the dimensions will need to be nearly exact of course because the location of were you touch needs to align perfectly with what is being displayed. So measure the dimensions exactly and look around. Look at aliexpress for example.

Also, if you think the problem is heat, you might have better luck with some kind of insulation instead of a fan. Or remove the power supply, put it in an external enclosure and make a cable using some control cable and CPC connectors.

 

[damien]

Thanks Bo, isolation material is a good idea! There's enough room to put a layer of isolation layer under the LCD board or even better an isolation material with a thin heatsink. I'll check What I can do with that. I thought about the PSU in an external case as well. It's a good Idea, I would just need to replace the IEC connector with a heavy duty connector or FPC at worst.

I checked the resistance on both failed digitizer and a brand new one and on the 4 pins with every combination while pressing it, I got open circuit so I don't know, maybe it's so small I can't measure it or maybe I did wrong.

EDIT: I can't get any reading because of course I probably need to have one line powered up.

 

[ccaudle]

on the 4 pins with every combination, I got open circuit

Check while something is pressing on the digitizer. I think most are like a simple x/y switch array, when press an x wire and a y wire will touch and make a connection, which of the 4x4 connections show the lowest resistance lets you determine the x/y coordinate where the touch occurred.

 

[Bo Deadly]

I checked the resistance on both failed digitizer and a brand new one and on the 4 pins with every combination while pressing it, I got open circuit so I don't know, maybe it's so small I can't measure it or maybe I did wrong.

I know nothing of these things but a very quick search turns up many suppliers. From there you can read the datasheet to understand how these things work. Here is an example datasheet:

https://www.nkkswitches.com/pdf/FT_Touch_FPCtails.pdf

If you scan over the scription, you can see that it uses an ADC to read a voltage. So it seems there is a bias voltage applied and the voltage on pins changes depending on where you press. This would suggest that it's some kind of capacitive voltage divider (just like a resistor voltage divider but with capacitors instead). So to actually test it, you would need to provide a bias voltage and then monitor the voltage on pins. But you probably can't just hook it up to a conventional DMM. The capacitance is very small the impedance of the measuring device would need to be quite high. If the input was say the mosfet gate of a microcontroller ADC, just the capacitance of the gate would influence things (it might be the capacitor in said "capacitive voltage divider"). But this is all wild speculation at this point. Spending 40 minutes googling would nail it down. I just don't have the time ...

 

[damien]

I'm looking on aliexpress for a similar size digitizer. There's some very close to mine for GPS displays with a different connector. Thanks for the suggestion, that would be a nice place to investigate. LCD is 3.5" visible, with a 3.7" LCD. I 'll check that later on! thanks very much for your input.

 

[damien]

Hi DIYers,

So yesterday I replaced the touch screen with a new one. I had the fan working at really low speed with a pot before but was probaby not efficient enough. I installed a Fan regulator to kick in above 40°c with the probe just above the PSU, it's going to be better this way.

For the one stumbling uppon this thread with the same issue here is the list of the parts I used:

Zhiu ZF3-1L 5-12V Fan regulator
ADDA DC Brushless 5V Fan AD0405HB-K90 (40 mm x 40 mm x 6 mm)

This regulator is really nice, I set it to work in silent/Gate mode. The Fan doesn't spin at all. When the T° goes above 40°c it kicks in at its minimum starting speed (higher than the min speed while already spinning, or it won't start but buzz). The regulator is set to work at max output Voltage for a 10°c range so 40°c is min Voltage and 50°c is max output Voltage. Probe is attached just above the PSU regulators on the cage.

This way the area around the PSU and LCD are kept at around 40° which is pretty standard for electronic operations. Human Temp don't kill electronics

The Fan is a 40x40x6mm ultra slim fan to fit along the PSU and the side pannel of the mixer. Not the best, but this is the only 5V 6mm fan I found online. I'll probably redesign the right side of the PSU shield cage to accomodate a bigger fan for minimum noise while spinning and better airflow.
I Thought about a blower fan pushing the air out to the bottom of the case from the left side of the PSU, there's holes in the case for that but those air blowers are efficient but really noisy if I remember.