On the logic board you will find all circuitry in charge of controlling the optical drive. You will find components on both sides of the logic board. We picture on Figure 23 the side you see when you first open the drive, which is the solder side.

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Figure 27: Logic board main components, solder side.

On Figure 28 you see the components side of the logic board.

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Figure 28: Logic board main components, components side.

The controller doesn’t drive enough current to turn on or move the optical drive motors. So all optical drives use a motor driver chip. This chip is a current amplifier. It takes the commands sent from the controller to the motors and passes them to the motors, but with a higher current. So, this chip is located between the controller and the motors.

The Flash-ROM circuit is where the optical drive firmware is located. Firmware is the name given to a program that is stored inside a ROM (Read Only Memory). The hard drive firmware is the program its controller executes.

There are two RAM chips in this unit, one with a very small capacity (128 KB) used by the controller which we labeled as “RAM” on Figure 28, and another one to store temporary data to be transferred to the computer, also known as buffer. The higher its capacity, the less vulnerable to the infamous “buffer underrun” error while recording CDs and DVDs your unit will be. Actually this error means that the buffer chip was empty. The larger the buffer, the lower the probability of buffer underruns.

You can find out the capacity of your optical drive buffer on the chip manufacturer’s website. For example, the memory chip on Figure 28 is a Hynix HY57V161610DTC chip. Going to Hynix’s website at http://hynix.com/datasheet/eng/dram/details/dram_01_HY57V161610DTC.jsp you can find this is a 16 Mb (Megabit) chip. The capacity of memory chips is given in Megabits, while we use Megabyte to refer to memory capacity. Thus we need to divide the value given in Megabit by eight in order to have the value in Megabyte. So, this chip is a 2 MB (Megabyte) chip, so this drive buffer is of 2 MB.

Usually to find out a chip function we just type in the numbers located on the first line of the chip package on Google and it will return a lot of information about the chip. But with our DVD burner we could find only information regarding the main processor chip, manufactured by NEC. The other chips, which were manufactured by Hitachi, we had to “guess” their functions, since we couldn’t find any explanation or datasheet about them on the web.

This “guess” however is not so complicated. First, the motor driver chip usually has a heatsink attached to it, so this one was easy to point out. Since all optical drives need a laser power controller (also known as RF chip), we just followed the wires from the optical pickup unit connector and found out that they were mainly connected to one chip, so we assumed that was the RF chip.

Since we were able to get the NEC processor (actually, a microcontroller) datasheet and we could see that this is a general-purpose processor, we assumed that the other big chip is the specific controller that “knows” how to control an optical unit. So we labeled it as “DVD+RW controller”.

If you'd like to learn even more about optical drives, we suggest you to take a look on the websites under http://www.repairfaq.org. That's a terrific place to learn more  about CD and DVD technologies and repair and laser technologies.