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Brighter backlight in UG-24U01 display (like in RU940), display repair
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Post 1 made on Monday March 8, 2010 at 15:28
Junior Member
March 2010
Hello everyone!

I recently purchased a defective pronto ru940. I spent a few hours to on the unit, and thought it might be interesting for some of you.

1. Display repair
When I received the unit, the screen was black (or white if the contrast dial was set to minimum). I disassembled the remote, got my magnifying glass, and had a look at the foil cables connecting the lcd itself to the printed circuit board. After some minutes of fruitless staring I discovered the error: The foil cable on the shorter side of the pcb was broken, causing a missing connection at half of the signal lines.
The foil itself is heat resistant, so I decided to start a repair approach.
I got some thin wire (pulled out of a UDMA/IDE cable), and soldered it over the broken connection. This is a hard peace of work. You'll need a good soldering iron an amount of patience comparable for the dissolving of one of those a rubic's cubes. Some experience in soldering 0.5mm pitch would be helpful, too.
After completing this task, I put everything together, replaced the batteries and - it worked!

2. Enhancing the backlight brightness
I was surprised how dim the backlight was. Hard to read, even in the evening. So I decided to improve it.
The backlight consists of a electroluminescent foil. A high voltage supply is needed to drive it. The display pcb contains all necessary components, so I didn't have to change anything on the main pcb.
Heart of the power supply is a HV823, an integrated power supply controller. According to the data sheet there is an easy way to raise the output voltage and hence the brightness of the foil: You can simply hook up the switching inductor used in this circuit to a higher voltage. The whole circuit is powered by the remote's internal 3.3V supply rail, switched by a transistor (might be a dual version) in a tiny SOT23-6 case. The easiest solution is to disconnect the inductor from the 3.3V rail by cutting the connection on the pcb surface with a sharp knife. Look for the connection between the SOT23 transistor (I can't read the stamp code, therefore I can't tell you more about this component). Then you can solder a thin cable to the inductor, and connect the other end of the cable to the "+" battery contact.
Please keep in mind that the battery is connected directly to the inductor now, without the switch philips designed between the battery and the high voltage supply. To make sure that the battery is not drained too fast I measured the current in the connection. It was approx. 1-2 µA, which should be no problem.

If anyone is interested in this issue, I can take some pictures of the pcb to illustrate what to do. Just let me know...


BTW: Please keep in mind that you'll have to pay with foil lifetime for the enhanced brightness...

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