C D R O M i n g (I)
I discoverd this drive mechanism in a Memorex CDRW drive (model CDRW 4420). This was built by Ricoh during the time where good R&D money was spent in developing optical drives. Not only does it show engineering sophistication, but it is also pretty good looking. Of the many CDROM drives I’ve dismantled, one would be proud to show this mechanism outside of the drive enclosure.
The typical mechanism is designed to be hidden from sight (because it is ugly) and most of them look similar to the one depicted below:
There is even a technical write-up published by Ricoh [link]. The model number for this optical drive platform is: Ricoh MP7040A. It was introduced in 1999 at a retail price of the US dollar equivalent of 500!
According to the report, the “pick up module” or PUM has been optimized for read/write speed and shorter seek time (good for data, but probably not important for audio). The picture below is from the technical paper.
The earlier optical drive mechanisms employ linear local regulation (as opposed to using switching regulators). Like most computer peripheral devices, it requires 5V/12V power. By tracing the power lines I found that the external 5V supplies the Renesas 2933 (3.3v) linear regulators and the external 12V supplies an 8V linear regulator.
According to the data sheet the 3.3 V regulator has a noise figure of 50 uVrms (10Hz- 100KHz). That is pretty good noise specification for a high current regulator. It is comparable to the LT1963 and way better than the common 78xx types. You can see here how regulators stack up in terms of noise figures.
Since this drive is over 10 years old, I changed the original electrolytic capacitors whenever possible. I added additional capacitors to the 5V and 12V input lines.
I made sure the drive continued to work after every mod and dis-assembly (I used a CDROM controller kit and listened through the headphone output).
Since the local regulators are linear, there is benefit of also using linear regulation for the external power. I built a simple dual 5V/12V power supply with standard fixed voltage 780x regulators. The transformer was salvaged from a VHS player. Old VHS player use linear power supplies and the transformer is perfect for this application: The typical transformer will give you (at least) two ~8V secondaries and one ~15 V secondary. The second 8V secondary can be used to power the CDROM drive controller kit.
The digital output comes from the Toshiba TC9450AF chip (I traced the spdif output pin to this chip). This chip is a servo controller chip. According to Toshiba [link]:
In response to speed-based competition in the CD-ROM market, Toshiba has developed a series of products that realize a playback speed of 32 times: the TC9450F digital servo one-chip processor; the TA2119FN head amp; the TC9466FA buffer RAM; and the TC9467F ROM decoder.
- Pin 1: Digital Gnd
- Pin 2: BCK (Bit clock)
- Pin 3: AOUT (Data)
- Pin 4: DOUT (SPDIF)
- Pin 8: CLCK
- Pin 100: LRCK
TESTING I2S SIGNALS
Luckily all the interesting pins are connected to board traces that also have vias. I used 30 ga wire through the vias and affixed them with electrical tape on the back side (no need to solder).
I used my new DSO to check the signals and got the following results:
- Pin 100: 44.4KHz (eye-balled) : confirmed LRCK
- Pin 2: 1.42MHz (eye-balled): This is 32x the sample rate. Confirmed BCK.
- Pin 3: Not a regular signal, meaning it is data modulated. Confirmed DATA
Trace for LRCK (Note, the scope has not been calibrated, or compensated, just updated with the latest firmware):
Trace for BCK:
Trace for DATA:
To be continued…