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| August 31st 2026 | Kasper Bergholt |
The photo shows a Trust 14K4 modem from around 1995, produced by the Dutch company Trust Computer Products, which is still in existence.
The modem in the photo was assembled in Taiwan. From around 1993 to 1996, I ran NetLock BBS using a similar modem from US Robotics, if I remember correctly.
The Trust one in the photo was the closest I could find reasonably priced on eBay for an archival project like this.
Maximus-based NetLock BBS was a Danish bulletin board system (BBS) running in the 1990s on the Maximus BBS platform, from a basement in Hillerød, Denmark.
It operated on a PC and ran around the clock (after acquiring a second phone line) with a 14,400 bps modem connection.
NetLock served as a digital home and community hub for early tech enthusiasts during the pre-web dial-up era.
Around 1996 my interests shifted, and I closed the BBS.
Camera: Nikon D3. Lens: Carl Zeiss 50mm f/2 Makro-Planar.
Sources on NetLock BBS
Kasper Bergholt on Github
NetLock BBS | pouet.net
NetLock BBS | Demozoo
NetLock BBS | Wikidata
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This is the circuit board of an external 14,400 bps data/fax modem from around 1995. The date codes 9549 and 9551 correspond to weeks 49 and 51 of 1995. The board is marked "WS-1414EV7G" and "Made in Taiwan", and the serial connector is made by Wieson.
1. UMC UM92144EF (large QFP chip in the center): The modem's main controller/chipset IC. It handles AT commands, data compression, error correction and coordination between the other chips.
2. UMC UM92960L and UM92961L (two square PLCC chips at the bottom): Part of UMC's "data pump" chipset. They perform the DSP work, i.e. modulation and demodulation of the signal on the phone line.
3. UMC UM92963 (elongated DIP chip): Probably an analog front end/codec that converts between digital data and the analog line signal.
4. Winbond W78C31BP-24 (PLCC, bottom right): An 8051-compatible microcontroller running at 24 MHz, which executes the modem's firmware.
5. 27C512 EPROM (large DIP chip with the "V0.10 / 169" label): 64 KB UV-erasable memory holding the firmware. The label indicates firmware version 0.10.
6. Winbond W24257AS-35: 32 KB static RAM with 35 ns access time, used as working memory and buffer.
7. Small 14/16-pin SO ICs near the DB25 connector: RS-232 drivers and receivers of the 1488/1489 type. They convert between logic levels and ±12 V serial levels.
8. Other small SO ICs (U8, U5 with "QC OK", U21, etc.): Logic, op-amps and support circuits, e.g. for audio and signal processing.
9. LM2575T-5.0: A switch-mode step-down regulator that supplies a stable 5 V to the logic.
10. 2A/250V fuse (glass fuse, top left): Protects against short circuits and overcurrent.
11. Large electrolytic capacitors (black cylinders): Smooth and filter the supply voltage.
12. Inductors (L2, L11, L12, etc.): L2 is the energy storage element for the switching regulator; the others are noise filters.
13. Diodes and Zener diodes (D7, ZD1–ZD6): Rectification, reverse-polarity protection and voltage clamping.
14. DC power jack ("POWER", top left): Input from the external power adapter.
15. NAIS relay (yellow): The off-hook relay, which "picks up the receiver" and connects the modem to the line.
16. Line transformers (KUAN HSI D1A050000 and the transformer with yellow windings at the bottom): Provide galvanic isolation between the modem and the telephone network while passing the signal through.
17. Optocoupler (near the relay): Detects the ring signal and passes it to the logic in isolated form.
18. Varistor/surge protector (black round disc): Protects against overvoltage, e.g. lightning strikes on the line.
19. Orange film capacitor: A high-voltage capacitor, typically used in the ring detector or for DC blocking.
20. Blue ceramic capacitors: Suppress high-frequency noise (EMI filtering) on the line and serial port.
21. 2 × RJ11 jacks ("LINE" and "PHONE"): One connects to the phone line, the other lets you plug in a regular telephone.
22. Crystal (metal can Y1): Provides the precise clock frequency for the chipset.
23. Speaker/buzzer (black, round): Plays the dial tone and call progress sounds, i.e. the classic modem "screech".
24. Rotary potentiometer (right side): Volume control for the speaker.
25. 8 red LEDs: Status lights, typically HS, AA, CD, OH, RD, SD, TR and MR (high speed, auto answer, carrier detect, off-hook, receive data, send data, terminal ready and modem ready).
26. DB25 connector (Wieson): RS-232 serial connection to the computer's COM port.
27. Transistors (TO-92, e.g. Q2, Q5, Q10): Small switching and amplifier stages, e.g. for driving the relay, LEDs and speaker.
28. Resistors and SMD capacitors (R and C numbers throughout): Decoupling, filtering, biasing and current limiting.
Some of the part numbers are hard to read precisely in the photo. This applies especially to the small SO ICs and the varistor, so those entries are educated guesses based on placement and function.
