Saturday, November 7, 2009

01/W FD Fix - LCD and FDD replacement (2009) Part3

I follow the smell and suspected the 3.5 inch FDD. I tested my 01/w after disconnecting the 3.5 FDD and the sound came back! However, strangely, all the sound from either program or combi sounded the same with no pitch-bend or modulation from joystick operation. I thought it was so because the sound data on the RAM was erased when I replaced the back-up battery on the main board. As I could not read the LCD, I just followed the manual step-by-step to reload the data from the default ROM of 01/W. The program and combi were loaded and the original sound was restored.

So, the source of the all the trouble began form the FDD. I guess the broken FDD is the cause of the LCD module damage as they share 5V power source. When I disassembled the FDD I could find a small burned electrolytic capacitor. As the part was Surface Mount Device (SMD) part, I could not easily replace the part. So, I decided to use a compatible 3.5 inch
FDD that is normally used on a PC.

I guessed the damage on LCD is irreversible because the screen status was the same when the FDD was disconnected and the sound was restored.

I searched the Web and found that someone did succeeded in replacing the Wavestation LCD module with compatible one with LED back-light.
(Refer to http://tellun.com/wavestation/wavestation.html)

I could get the same LCD module but could order from an online LCD shop, which sells one with similar spec. You can download datasheets and compare them before ordering. And don’t forget to compare the external and viewing area dimensions as there are some LCD modules with same dot matrix but different dimensions. (LCD module with LED back-light is a bit thicker than the original one but it can fit without problem)

There are many different kinds of LCD backlights. I prefer blue background and white characters as below.






You should make two modifications to use the compatible LCD module. As the original module and new one use the same graphic controller, the 1~20 pins are almost the same but the negative voltage to Pin-4 is a bit different for new LCD module. The original one requires about 13.5V difference (voltage difference between negative voltage from main-board’s Pin-4 and Pin-3 (5V for LCD logic power supply) for LCD contrast control . It means the original negative voltage from main-board’s pin-4 centered around -8.5V. The new one requires about 12~12.5V difference depending on brands and models (refer to manufacturer’s datasheets).

I used CBG24064A14-BIW-R from Chenzen AV Display (China).
(Refer to http://www.av-display.com.cn/en/default.aspx)
It is easy to find in Asian region such as in Korea and I ordered it from FINDLCD.COM. I used this one because the spec was similar to the Newheaven model, which was used
In the above mentioned Wavestation.

Compared to the Wavestation modification, I used 5K ohm one single turn trimmer (variable resistance) instead of using two resistances (3.9K and 698 ohm) to adjust the negative voltage from the main-board’s Pin-4 voltage source to Pin-4 of LCD. I used the variable resistance because the LCD models are different and they require a little bit different voltage for Pin-4.

I tried to understand the simple two resistance voltage adjusting circuit but could not completely understand it. I just guessed following circuit increase the negative voltage to the pin-4 of the LCD.

Main-board Pin-4 (-8.5 V) -- R1 (1K OHM) -- Pin-4 of LCD -- R2 (4K OHM) – PIN2 (Ground)
(You can adjust the variable resistance to get optimal contrast control voltage)

The ground is 0V and the combination of two resistances or one variable resistance will increase the -8.5V to around -7V to make the 12V difference (-7~+5V).




There is no appropriate place to weld the chassis ground line (green and yellow). So I welded it to Pin-1 directly. The hardest and time-consuming part of the replacement is welding the 19 pins (Pin20 is not used, I used heat-shrink tube as above). The middle lead of the variable resistance goes to Pin-4 of LCD, the other two leads connect to Pin-4 of M/B and Pin2 of LCD. It seems that taking the black 20pin connector as a whole out from the original LCD module and putting it on the new one is neater. I tried doing so but failed because tapping the cable for Pin-4 in the middle was not easy. I just cut the cable and welded step by step.

The other modification is back-light power 5V. The original module uses CCFL back-light , which requires high frequency, high voltage power that the converter circuit part on the power supply board supplies. The new one uses more durable LED back-light and its operating voltage is about 3.2V~3.5V (I guess it uses parallel array of LEDs). We need to supply higher than the operating voltage but the brightness of LEDs are controlled by the current and if current is too high, it will result in short life of the LEDs.

When I calculated optimal resistance using Ohm’s law, it was about 15 Ohm.

(5 – 3.2) V = 120mA (optimal current from datasheet) X R Ohm

R = 15 Ohm

However, 100 ohm was used for the Wavestation’s Newheaven LCD. So, I also used 91 Ohm (100 Ohm was sold out) and the brightness was just enough. It would be better to use higher resistance than the calculated 15 ohm because it is safe and good for LED’s life as long as it is bright enough. I used 1 watt class resistance because I heard resistance for LCD connection needs to be relatively high wattage and the back-light uses parallel connection of LEDs (even higher wattage). The LCD seller recommended 1 watt class.

You should remove and the transformer (TA042) and connect from 5V source to connector pin (white) to prepare the power source for the new LCD.





(Above : transformer removed and a resistance(90 ohm) was installed.

1 comment:

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