Replacement LCD display for the Alesis Fusion

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Re: Replacement LCD display for the Alesis Fusion

Postby 2ManyKeys » Wed Apr 25, 2018 7:52 am

The new screens from MPJA are a "transflective" type which means they are not as easily backlit and usually not as bright with a backlight but they reflect ambient light better and are usually easier to see in brighter conditions. With these new displays you should be able to read the LCD clearly even in sunlight.

This display type is great in low light and bright ambient light but not as good in normal lighting.

Something I may well do is add a backlight switch when I mod my Fusion. These displays actually lose contrast under certain lighting conditions when the backlight is on. So if you have a nice overhead light above the Fusion, being able to shut off the backlight might actually improve visibility.

I will be doing the LCD replacement in the near future as I just ordered an 8HD.
Last edited by 2ManyKeys on Wed Apr 25, 2018 11:44 am, edited 1 time in total.
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Re: Replacement LCD display for the Alesis Fusion

Postby 2ManyKeys » Wed Apr 25, 2018 11:39 am

It is strange to find a transflective display this large which is probably why MPJA had them so cheaply. Transflectives are generally becoming less popular.

Everything you might want to know about. transflective displays.

https://focuslcds.com/journals/lcd-pola ... nsmissive/
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Re: Replacement LCD display for the Alesis Fusion

Postby Jesse » Wed Apr 25, 2018 6:34 pm

you should be able to use the dimmer switch to turn the backlight way down
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Re: Replacement LCD display for the Alesis Fusion

Postby 2ManyKeys » Wed Apr 25, 2018 8:13 pm

Cool. I didn't know if the retro fit for the dimmer allowed that much dimming range.

Truth is, this display type might be better lit by a front mounted group of LED's that shines down on the LCD.
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Re: Replacement LCD display for the Alesis Fusion

Postby neomad » Sat May 12, 2018 10:18 am

Hi guys,
Even with the dimmer switch light is pretty low. I do not know what is happening.
I do have another display, I will switch it just in case the first one does not work properly.

It is clearly not a problem of dimming but retro light.
Keep you posted ;)

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Re: Replacement LCD display for the Alesis Fusion

Postby Jesse » Sun May 13, 2018 6:46 am

If you are using the 3.5 volt source you can try connecting to a 5 volt source, but the dimmer control may not work
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Hantronix LCD install improved!

Postby 2ManyKeys » Sun May 13, 2018 8:35 pm

So, after solving my partition issues and finishing the SSD install, I was all about replacing the LCD. This took a while as well. I used the Hantronix module sold by MPJA that is listed earlier in this thread.

Before installing the new display I spent some time with a variable power supply and some power resistors determining what current levels provided good illumination without getting the LED module too hot. I found that between 150 and 200mA the backlight was nicely bright while still running cool. At 300mA and above the LED module got too hot. I can tell you the datasheet provided by MPJA has the wrong LED backlight specs. This white LED would never survive at 900mA or 2A unlike the green one specified in the datasheet.

With that information in hand I took a closer look at the two connectors that connected to the stock CCFL backlight inverter. The smaller of the two indeed provides about 3.4 volts. Jesse and others mentioned connecting this directly to the new LED backlight. I did that and found it was nowhere near bright enough. Truth is, 3.4V is barely enough to turn on the LED's which is why they remain fairly dim and fortunately don't hit high currents and blow up. I should note that this "turn on" region of the backlight is rather nonlinear so each backlight will act a bit differently. The unit I was using is quite dim with the 3.4 volt supply. Others might be a bit brighter. In any case though, the LED module is not getting into it's fully-on region of around 4V.

Remember an LED is just that, a Diode that emits light. That's why an LED should never be hooked up directly to a supply. A diode goes from it's off state to it's conducting state when it reaches it's conducting forward voltage threshold. Once the threshold is met the diode or LED becomes a very low impedance current path much like a short. Hook this same backlight up to 5V without a dropping resistor and it would have a very bright, short life. We once had a new engineer at a place I worked who kept returning LED's to the component group explaining that they were very bright for a while but kept going bad. When the experienced component engineer figured out that the new guy was simply hooking them directly to the supply he just about killed the kid. :-)

Here's a nice summary of how diodes work. Note that once you hit that forward voltage threshold the current literally goes through the ceiling.
https://learn.sparkfun.com/tutorials/di ... cteristics

Okay, so the larger power supply connector that connected to the inverter board supplied 12.5V no doubt directly from the power supply. Even though this voltage is a bit high, I knew that after removing the original hard drive and replacing it with a 5V SSD, there was now plenty of headroom on the 12V supply rail as the hard drive had been the main 12V load. The other problem with the 3.4 volt connector is that it is output from the "3.3V" supply rail for the processors and DSP's. So even if the voltage had been high enough, the amount of current that could safely be drawn from the 3.3V supply is unknown. If that rail droops, the whole system would become unstable and start crashing.

I fished around till I found the right power resistor which I calculated to be around 50 Ohms. I found a 56 Ohm, 10W resistor that was perfect in that it wasn't physically too large but also would not develop high surface temperatures with the limited current load I was going to put through it. Upon testing this provided exactly 150mA current through the backlight providing nice bright backlighting and staying cool. At this current, the whole backlight system, LED and power resistor dissipate about 2W. The power resistor has an 8.6V (1.2W) drop across it meaning that at this current, the LED's have 4V across them. You simply can't get enough current through that 3.4V line to properly turn on these LED's. You'll note that actually more power is being dissipated by the power resistor than the backlight! True, but there was no convenient 5V supply available on that board and again the amount of headroom on the 5V rail is unknown as well. Using the 12V supply wastes a bit of power but it's the safest solution considering the whole system.

Fortunately the relatively small aluminum power resistor mounts nicely to one if the same holes that was previously used by the inverter board. I did have to drill out one of the resistor mount holes a bit to use the stock screw.

Here is an example of a similar power resistor at Mouser. These are common and easy to find.
https://www.mouser.com/ProductDetail/AR ... 80IJb1w%3d

NOTE: To be safe, all connections including the ends of the power resistor were insulated with heat shrink tubing.

So, after replacing the hard drive and the LCD my Fusion now pulls a stable 27W which is a full 25% less than the stock 36W draw!
That's huge and will no doubt make things easier on the supply hopefully contributing to it's longevity.

So for those of you who already did the display replacement and want it to be bright, this is how it's done.

Here are a few shots of the LCD install and power resistor. The shot showing the LCD operating makes the text look washed out. It's not, I just wanted to illustrate how bright it is.

Well, for whatever reason the board keeps telling me that the images I'm trying to upload are invalid. :-(
Jesse? The file size was to large

20180513_213749 Scott Tribbey 01a.jpg
20180513_213749 Scott Tribbey 01a.jpg (871.44 KiB) Viewed 108 times


2018513_1260 Scott Tribbey 02a.jpg
2018513_1260 Scott Tribbey 02a.jpg (892.74 KiB) Viewed 108 times


2018513_1259 Scott Tribbey 03a.jpg
2018513_1259 Scott Tribbey 03a.jpg (973.09 KiB) Viewed 108 times
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