TEAC PD-155
A compact disc player with a motor-driven drawer, a three-beam laser, and a service manual that expects you to own an oscilloscope.
Audio publications of the late 1980s regularly grouped the PD-155 with the era's other compact disc players in their buyer's guides and product roundups. Coverage appeared in Audio (October 1988, p.164) and HiFi-Stereo (October 1988, p.122).
Overview
The PD-155 treats the disc as a precision optical problem first and an audio source second. TEAC's own manual lays out the guts plainly: a three-beam laser pickup, CIRC error correction, and 16-bit linear D/A conversion at the standard 44.1kHz sampling frequency. That's the baseline every first-generation CD player was built on, and the PD-155 doesn't pretend otherwise.
The loading mechanism is motor driven and horizontal. The drawer slides in and out on its own instead of relying on the user to push it home. The output stage is specified at 2Vrms maximum, which is on the hot side for a CD player and gives downstream gear plenty of signal to work with. Channel separation is listed at more than 75dB at 1kHz, and the signal-to-noise ratio at more than 80dB. That's respectable for a player of its generation, though neither figure is exceptional by the standards of later decks.
Frequency response is quoted at 20Hz–18kHz, ±1dB. That top end will raise eyebrows today, but it's worth remembering that the CD format's theoretical ceiling is 22.05kHz, and plenty of players from this era rolled off well before that. Harmonic distortion is specified at less than 0.07% at 1kHz, which is a figure that looks modest next to modern gear but was entirely normal for the period. Wow and flutter is described in the manual as "quartz precision," which is TEAC's way of saying the clocking is crystal-controlled and the mechanical speed variation is effectively nil. In practice, that's the whole point of digital playback — the transport's job is to deliver bits, not to sound like anything.
The feature set is where the PD-155 shows its age. Program functions cover up to 16 selections, with repeat for all tracks or just the programmed ones. There's instant program selection with music skip via the ▶▶I and I◀◀ buttons, and a separate search/index function using the ▶▶ and ◀◀ buttons — though the manual notes that index search only works in stop mode. Forward and backward scanning is done with sound, which was a novelty at the time and remains a useful way to find a specific passage without staring at the display. Reset is a press of the STOP button, and pause is available for each selection. None of this is exotic, but it's a complete toolkit for the way people actually used CDs in the late '80s.
Physically, the PD-155 measures 435×90×290mm and weighs 3.4kg. That's a standard-width component footprint, so it sits in a rack next to a receiver and a cassette deck. Power consumption is listed at 9 watts. The manual covers multiple voltage variants: 120V/60Hz for Canada, 220V/50Hz for Europe, 240V/50Hz for Australia and the UK, and a 110/220V 50/60Hz export version. General export models have an AC selector on the rear panel, accessible by removing a screw and a plate, so the same chassis could be configured for different markets.
Much of the service manual is devoted to keeping the player alive. There's a full procedure for checking the focus error signal. You connect an oscilloscope between test pin FE and ground, feed +10V through a 47kΩ resistor to the FOFF pin, and watch for a waveform that appears six times as the tray closes. The peak-to-peak voltage should be about 8V, and the top and bottom of the waveform should be symmetrical. If you can't get that confirmation, the pickup is faulty. That's a bench procedure, not a diagnostic flowchart.
The alignment section is even more involved. There are five variable resistors on the main board, all set to mechanical center from the factory: P101 for E-F balance, P102 for focus offset, P103 for tracking offset, P104 for tracking gain, and P105 for focus gain. The manual walks through free-run frequency adjustment. Short the boss terminals of C114, connect a frequency counter between the VCO test pin and ground, and rotate the core of the PLL OSC coil T102 until the counter reads 4.3218MHz. That's the master clock for the whole system, and it's adjustable with a plastic screwdriver. Focus offset is set by adjusting P102 until a DC voltmeter and oscilloscope read 0V ±10mV between TP07 and ground. Tracking offset is set to 0V ±50mV. E-F balance is set to 0V ±50mV.
The manual also covers the diffraction grid observation procedure, which verifies that the three beams from the laser pickup are aligned. The E and F beams need to be on the same pit line as the main beam. To check that, you short test pins TP17 and TP18, short TOFF to ground, pass the E and F signals through a band-pass filter, and connect them to a dual-trace oscilloscope. Play the fourth selection on the test disc YEDS4. The trigger of waveform F should be approximately 30µs behind the point where waveform E hollows out. If it isn't, the beams aren't aligned.
Jitter confirmation is listed as optional. The manual says it can be omitted if no jitter counter is equipped. If you have one, you connect it to the EFM test point and check that the 3T value is less than 25nSec. If it's 25nSec or more, you adjust P102. That's the same focus offset pot you set earlier, so the alignment is iterative rather than linear. You set focus offset, check jitter, then you might need to go back and adjust focus offset again.
The turntable height adjustment is another mechanical detail. The manual specifies that the turntable should be attached so its top surface is 14.05mm from the top of the chassis, and that this adjustment must be made when the motor is replaced. The focus gain and tracking gain adjustments have both a simplified and a precise procedure. The precise version requires a measurement circuit that most people won't have. The simplified version sets P105 and P104 to positions 15° from mechanical center, which is a starting point rather than a final answer.
The manual also notes parts changes by serial number. Several parts moved from the main PCB assembly to a newly made sub PCB assembly at specific serial number thresholds: 801795 and after for US models, 800301 and after for Canada, 801501 and after for Germany and Europe, 800201 and after for the UK, and 800001 and after for Australia. If you're sourcing parts or matching a schematic to a specific unit, check the serial number first.
The safety certification section is in five languages and carries the standard warning about low-power laser devices. Don't remove the covers, refer servicing to qualified personnel, and be aware that using controls or adjustments other than those specified can result in hazardous radiation exposure.
The manual is written for someone who owns an oscilloscope, a frequency counter, a test disc, and a set of plastic alignment tools. It assumes you'll check the focus error signal before you replace the pickup, set the free-run frequency before you chase a tracking problem, and verify the diffraction grid before you decide the laser is dead.
Whether the PD-155 sounds good is almost beside the point. The specs — 20Hz–18kHz, 0.07% THD, 80dB S/N — are competent but not remarkable. What's remarkable is that the thing was built to be kept running. The alignment procedures are documented. The test points are labeled. The serial number breaks are noted. If you're the kind of person who owns a scope and a test disc, the PD-155 is a player you can actually work on. If you're not, it's a decent-sounding CD player from the late '80s that will probably outlast a lot of newer gear simply because it was made to be fixed.
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