Turbo Grafx CD-ROM Drive
- IC101: CD RF Amplifier: CXA1081M
- IC102: CD Servo Signal Processor: CXA1082BQ
- IC103: 4558
- IC104: CD Power Driver: BA6290A
- IC105: CD Power Driver: BA6290A
- IC106: CD Digital Signal Processor: CXD1135Q
- IC107: SRAM: CXK5816MY-15L
- IC108: D78C140F
- IC109: D9309GF
- IC110: D4364G-12L
- IC301: +5V Regulator: 7805
C101 100uf 6.3v C102 3.3uf 25v C113 33uf 6.3v C114 33uf 6.3v C117 3.3uf 25v C122 100uf 6.3v C127 4.7uf 16v C129 22uf 6.3v C136 100uf 16v C139 1uf 50v C149 100uf 6.3v C159 47uf 6.3v C200 22uf 6.3v C201 100uf 6.3v C202 100uf 6.3v C205 10uf BP 10v C206 10uf BP 10v C215 4.7uf 16v C216 4.7uf 16v C219 4.7uf 16v C220 4.7uf 16v C223 4.7uf 16v C224 4.7uf 16v C226 100uf 6.3v C229 100uf 6.3v C300 470uf 16v C301 470uf 16v C302 100uf 6.3v C303 100uf 16v C304 100uf 6.3v
CD Test Points
The test points are marked on the underside of the PCB, grouped into two connectors.
- Pin 1: ASY
- Pin 2: TE
- Pin 3: GND
- Pin 4: RF
- Pin 1: PLCK
- Pin 2: 2.5v
- Pin 3: TE-O
- Pin 4: FE-O
- Pin 5: FER
- Pin 6: TER
From left to right, PCB facing down. Note the out of order numbering.
- VR101 - E/F Balance (CXA1081, pin 12, 13)
- LASER CONNECTOR
- VR102 - Focus Error (FE) / Focus Offset Bias (CXA1081, pin 18)
- VR105 - VCO (CXA1082, pin 30)
- VR103 - Tracking Gain / Tracking Error (CXA1082, pin 45)
- VR104 - Focus Gain / Focus Error (CXA1082, pin 48)
You shouldn't have to adjust VCO, but if someone has gone in and wildly twiddled the adjustments, VCO may need to be readjusted.
- Disconnect power
- Place frequency counter on PLCK at P104, pin 1
- Connect ASY on P103 to ground
- Connect power
- Set VR105 for a reading of 4.3Mhz
I don't have a published spec, but a reading of ~4.3 - 4.4Mhz seems to work across a variety of test discs. I measured an almost-new Turbo CD drive and recorded 4.295Mhz.
I've found two methods of determining if VCO is set correctly:
Method 1: Audio CD bench test
- On the bench, put a long length (70 minutes+) audio CD in the drive.
- Press play
- Tap the side of the drive until a skip is forced.
- If audio resumes normally, skip to the last track on the disc
- Tap again and force a skip
- If audio resumes normally, VCO is roughly correct.
If the audio become choppy after a skip, VCO is incorrect. Tweak until both inner and outer tracks resume normally after a skip.
If the audio disappears completely after forcing a skip, something else is incorrectly set.
Method 2: FMV game test
- Dock the CD Drive and put in an early title that makes heavy use of FMV, such as It Came from the Desert
- If long videos briefly glitch out but otherwise the drive seems fine AND the disc is clean, it may be due to an incorrectly set VCO.
It appears that the early programs written to stream video are intolerant of buffer under/over runs, so if the disc speed is incorrect, you can get a video that will briefly glitch out, usually accompanied with a harsh white noise in the audio, and then the sequence will end prematurely.
One of the more frustrating problems with the TG16 CDROM is that some drives seem to be prone to having the laser get stuck toward the outside of the disc.
To help prevent this condition, when you're done using the system, remove the CD from the drive and look for the laser eye. If the laser is not next to the spindle, power the system off and back on again, and with the lid closed, press Run on the controller. This will bring the laser back to the inner track area and keep it from getting stuck the next time that you use the system. Cleaning and relubrication can help prevent this condition.
I have created a visual guide to disassembling and reassembling the CD gears.
Before making any tracking adjustments, it's probably a good idea to clean the gears of any old lubricant and reapply fresh lubricant.
The plastic gears SHOULD NOT be lubricated. Added lubrication will collect dust and gum up the gears. At worst it could ruin the gears if a plastic-incompatible lubricant is used. If you add a lubricant with shear-thinning properties, at first everything will seem to run great, until you try to use it the next day and the motor won't be able to turn the gears. The factory didn't apply lubricant to these parts, presumably because they are a self-lubricating plastic like nylon.
The brass worm gear and the cluster gear shaft were the only parts lubricated by the factory. Use an appropriate light grease for electronics, moly or silicone based. The opinions regarding the best grease vary widely, and I can't say I have any particular opinion in the matter. Don't forget to clean the gunk out of the laser's nylon follower that clamps onto the worm gear. This is accessible from above, by removing the large black metal plate the covers the laser & spindle assembly, and removing a single screw in the laser assembly.
I have observed minor wear on the brass worm gear where it seats in the top hat bushing, but I would not add any lubricant to this spot. The worm gear needs to be able to move in and out of the top hat bushing just slightly. If you add lubricant, air won't be able to flow freely and you can get into an air bubble / vacuum situation. This can cause the laser to get hung up at the end of its travel.
You may also wish to lubricate the cluster gear shaft, but at this time I don't yet have any long-term observations to draw from. A very thin coating should be sufficient.
The rail that the laser slides on should also be cleaned and lubricated.
Adjusting Motor Gear Mesh:
The 2 screws that hold the motor into the frame of the laser assembly can be adjusted to improve gear mesh, reducing noise and prolonging the life of the fragile cluster gear.
After you've properly cleaned and relubed the mechanism, spin the cluster gear back and forth with your fingertip. Do so delicately, and do not use tools or you may damage the teeth.
While spinning the gear back and forth, adjust the tension on the motor screws until the least amount of resistance is felt in the gears.
If you find that the optimal setting requires one of the screws to be loose, use tape to shim the frame so that alignment is maintained when the screws are tightened.
These are adapted from the specs for the NEC CDR-35, which is based on the same hardware design as the TG16 CDROM.
Maximum Data Capacity: 540 MB Data Transfer Rate:150K Bytes/Sec Access Time: 1500 ms Error Rate:<10 MTBF:15,000 Hrs Sampling Frequency: 44.1KHz Frequency Response: 20Hz-20KHz Dynamic Range: 76db Total Harmonic Distortion: 0.7% Channel Serperation: 70dB Output: 1.2V Phono Jack: on disk unit