Turbo Grafx CD-ROM Drive

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P/N: 03377077

Chip Info

  • IC301: +5V Regulator: 7805


Capacitor List

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.

  • P103
    • Pin 1: ASY
    • Pin 2: TE
    • Pin 3: GND
    • Pin 4: RF
  • P104
    • Pin 1: PLCK
    • Pin 2: 2.5v
    • Pin 3: TE-O
    • Pin 4: FE-O
    • Pin 5: FER
    • Pin 6: TER

CD Adjustments

From left to right, PCB facing down. Note the out of order numbering.

  • VR101 - E/F Balance (CXA1081, pin 12, 13)
  • 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)

Setting VCO

You shouldn't have to adjust VCO, but if someone has gone in and wildly twiddled the adjustments, VCO may need to be readjusted.

  1. Disconnect power
  2. Place frequency counter on PLCK at P104, pin 1
  3. Connect ASY on P103 to ground
  4. Connect power
  5. 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

  1. On the bench, put a long length (70 minutes+) audio CD in the drive.
  2. Press play
  3. Tap the side of the drive until a skip is forced.
  4. If audio resumes normally, skip to the last track on the disc
  5. Tap again and force a skip
  6. 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

  1. Dock the CD Drive and put in an early title that makes heavy use of FMV, such as It Came from the Desert
  2. 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.

Stuck Laser

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.

Re-Lubrication Guide

Consider cleaning & relubing the gears with this visual guide

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