Below are a few examples for users as references:. Increase output capacitance values to reduce the output ripples: this method is simple and straightforward, but the drawback is the increase of cost. Change the PWM dimming frequency to avoid the audible frequency range, which is about 20 kHz. However, the drawback is dimming linearity will be compromised.
Replace with an MLCC from the noise reduction solution: The output capacitance will affect how large the ripples are. Large ripples may cause resonance in between the layers, which will induce noises. The noise-reduction capacitors have the superior performance over the cross-voltages, that is, less capacitance change at higher DC biases. Figure 10 shows the comparison of the equivalent MLCC capacitances between the new noise-reduction and conventional fabrication processes.
Figure The comparison of MLCC equivalent capacitances between new and conventional fabrication processes. For some models, only the short channel will be off, while for others, it is the driver circuit to be turned off.
It will clamp the output voltage at the voltage set by OVP, without turning off the circuitry. Figure 12 shows the RT protection mechanism flow.
In recent years, the features of 3D and local dimming have been incorporated in high-end TV models. They are to be introduced as below:. In 3D mode, due to the decreased PWM duty, the higher brightness from backlight modules is needed.
Figure 13 illustrates a 3D dimming functional diagram. This approach is used for advanced models to enhance the contrast. The blacks with local dimming are perceived darker because the backlights of that section are dimmed. On the contrary, the backlights behind brighter sections can be brighter. Henceforth, local dimming has the advantage of consuming less power. Figure 14 illustrates an example of a zone local dimming.
The more zones the screen is divided into, the more noticeable the benefit of local dimming is. However, the trade-off is the complexity of control and cost will be correspondingly increased.
For local dimming applications, the limited bandwidth of the commonly used I2C Interface is no longer acceptable. The architectures for LED backlight driving systems vary in accordance with various requirements, such as energy efficiency, cost down and performance enhancement.
The driver ICs should then be changed accordingly. Finally, to tackle the audible noises, to enhance the system efficiency, and to meet the surface temperature requirements for all the components are also important aspects to consider for customers.
Figure 1. Edge-Lit Type vs. Direct-Lit Type Backlighting Backlight Modules, as the lighting source of LCDs, consist of light sources, light guides and backlight diffuser plates, etc. Figure 3. Edge-lit Backlight Module For direct-lit backlighting technology, LEDs are placed in a flat array behind the light guide plate and the LCD screen, which the light is directly emitted to.
Figure 5. The application schematic diagram of a power solution Dynamic Headroom Control DHC function is created for this purpose. Figure 6. Programmable soft-start capability is available for both the primary TFT supply and LED driver to control the inrush current. Figure 1. The panel is not activated and stays in a low current state until V ON is present. This delay gives the column drivers and the digital part of the LCD panel time to get ready before the panel is turned on. The fourth switcher in the LT is a boost regulator designed to drive up to 20 LEDs in two strings to power the backlight.
Figure 2 demonstrates the current matching between the two LED strings. Proper layout is important to achieve the best performance. The power cable for the backlight was soldered to the output side. Before attaching the electronics together, I tested every individual piece separately.
For the back light this meant testing with 16 volts from the bench top power supply. The DC boost converter was tested with 5V from the power supply, and I adjusted the voltage so that the output was set to 16V.
This step is critical — just blindly connecting to the boost converter will most probably result in overvoltage that will destroy the backlight.
After this I connected the backlight to the boost converter, still powered from the separate power supply. Finally the boost converter was connected to 5V power from the sampler, and the sampler was powered on. No surprises here, everything worked. After the test, the components were disconnected and each attached separately to the sampler. The backlight was slid into the LCD panel.
Next the LCD panel was screwed in place. The best way to do this is to first attach the two screws on the right, then slide the LCD panel in place and make sure the top screw goes behind the backlight, attach the screws on the left side to secure the LCD in place, and finally tighten everything. Remember to connect also the LCD cable. In order for the boost converter to fit in place of the original inverter, I cut a piece of scrap PCB board.
The positions for the holes in the inverter and in the boost converter were marked there and drilled with a 3 mm drill bit. After this, the boost converter was attached to the PCB with some raisers and screws, and the raisers of the original inverter board were attached to the other side of the scrap PCB piece.
At this point I did some final adjustments for the backlight brightness. I ended up to use about This might require higher level of brightness, but I was OK with the original blueish color.
The cable for the backlight needs to take a slightly different route than the original EL backlight cable. There is a tiny part of flexible ribbon cable between the connector and the backlight. In order to avoid stressing this part, the cable was attached to a post in the front part of the sampler body with a zip tie. The cable has to be routed carefully through the opening in order to avoid damaging the weak spot! When the LCD was in place, the front cover was closed and the five screws on the top were installed back in place.
Next the boost converter was attached with the original screws in the same place where the inverter used to be, and the power cables were connected to it. As all cables were now back in place, they were tied together with a zip tie like they used to be. Then the top cover was closed, three screws at the bottom of the front panel were put back in place, and the volume knobs pushed in their shafts. A quick test drive revealed no problems. The backlight was bright and even, and there was no disturbing noise anymore.
This was not only a repair but an upgrade! I had to do some post-processing and adjust the overall brightness of the images to match each other. I prefer to do modifications to the vintage equipment so that they are fully reversible, and this is such upgrade as well.
Apart from a zip tie that had to be cut, no original parts were damaged. All parts for this upgrade could be obtained for as little as euros. This repair is not limited to just this specific sampler model, but any equipment that uses EL film for LCD backlight.
Cutting a mobile phone backlight to required shape is easy, and as long as the LED strip is not damaged, wide variety of display sizes can be targeted. I would suppose some tablet backlight could be used for even larger displays than this. There could be opportunities for utilising these backlights for wearable electronics or cosplay as well.
The backlight is slightly flexible, but the thickest film will break if bent too much, so some reinforcement may be needed in those use cases. It seems that these are occasionally available. Very detailed explanation and a lot of useful info for we, the old Akai samplers users! I have to try this, as a whole display replacement seems to be impossible to find.
Thank you very much for sharing info! Like Like. Thank you so much for sharing this. This is of great value for oldschool sampler users, who do not want to give money to the many greedy replacement parts sellers out there.
I have just cut the backlight to shape — still works, yay — and was wondering what kind of tape you have used to seal the edges. Standard electrical tape does not seem to stick properly. Many thanks and best regards. Great info! Once you have finished with the project, I can add a blog post with your pictures. Just drop a message here when you are ready. This is a great, detailed walk through. The DC to DC boost converter replaces the original inverter.
Like Liked by 1 person. Hi — a very useful and concise guide, thanks. There are connectors for both cables of the inverter. This naturally applies if you use a full replacement inverter module. Akai S has a different and smaller LCD screen. Where was the LED backlight supplier on ebay? Thank you for documenting this so clearly. I just followed your example but in an Akai MX master keyboard.
It uses the same display. So good to get rid of that whining inverter! I cracked the backlight while cutting it so have just ordered a new one. Would a 2A DC step up like this work? Sorry it took long time to reply.
0コメント