Teardown: Platinum Tools LANSeeker TP500

-November 15, 2017

Having recently reviewed the TP500 LANSeeker from Platinum Tools, I figured it's time to take it apart. It's mostly a microcontroller, some LEDs, driver components, and a DC/DC converter.

At first look, you might be tempted to assume that the LANSeeker's case snaps shut and can't be opened without damaging the case. Still, you can't open it without leaving evidence of tampering because the main unit's three screws and the remote unit's single screw are hidden under their front labels. Peeling back the base unit's label (Figure 1) revealed two screws, but not the third.

Figure 1 Screws are located under the labels.

With the case open, the single board (Figure 2) is accessible.

Figure 2 The main unit's PCB connects the the cable under test and to a 9 V battery.

The heart of the LANSeeker is a PIC16F722A-I/SO microcontroller from Microchip. It stores 2048 words in flash memory had has up to 25 I/O pins. The I/O pins can source and sink enough current to drive LEDs directly.

The corner of the board holds the power circuits (Figure 3). U5, marked "OE HH" is a ELM1117HH or similar, a 1 A, low dropout (LDO) voltage regulator that drops the battery voltage down to 5 V. A 220µF; type AHA capacitor (C5) filters the regulator's output. D11 is a BZX84 series Zener diode across the LDO's output and is in parallel with C5 and C2. Q5 (also used in other places) is a BSS84 MOSFET.

DC/DC converter circuit
Figure 3 The DC/DC converter consists of a low-dropout regulator and filtering capacitors, among other components.

Moving toward the RJ-45 connector, we see a 74HC4351D 8-line mux (Figure 4). This device most likely is used to select and push test current to the four pairs of lines from the RJ-45 connector. The eight 100 Ω resistors connect to the mux to limit current. Devices U1 and U2 are SRV05-4 transient voltage suppressors that protect the circuits from transients and ESD on LAN cables. U3 appears to be an MMBD1501A diode based an a search of the A11 marking. That seems odd to be designated U3 given that all other diodes are designated with "D." The via between R17 and R18 runs to capacitor C1. The same pin also connects to U2 pin 5.

74HC4351D multiplexer
Figure 4 A 74HC4351D connects to the RJ-45 and selects wires on the cable under test.

While Figure 4 shows three of the five LEDs on the main unit. Figure 5 shows a close up of the LEDs. D5 is the shield indicator. The cables I used in my tryout lacked shields.

TP500 base unit LEDs
Figure 5 D1 corresponds to RJ-45 pins 1&2, D2 covers pins 3&6, D3 indicates the status on pins 4&5, and D4 indicates pins 7&8. D5 indicates a good cable shield.

The section of the board below the µC (bottom section in Figure 1). Contains the test-result LEDs—short, miswire, reversw, split pair— as well as the tone generator. The hole in the board is for the rubber pushbutton. Figure 6 shows that section, which include three more BSS84 MOSFETs.

tone generator circuit
Figure 6 This section contains circuits for the tone generator and for the test-result LEDs.

Inside the remote unit
Peeling off the remote unit's label reveals a single screw holding it together. The LEDs in the remote unit (Figure 7) get their drive current from the base unit through the cable under test. Diodes D2, D5, D6, D11, D12, and D13 are BZX84-B30. D3, D5 D9, and D10 are the commonly used MMBD4148.

LANSeeker remote unit PCB
Figure 7 The remote unit contains LEDs and steering diodes.

The LANSeeker is an easy-to-use LAN cable tester whose base unit consists of a single board that controls the tests, drives the indicator LEDs, and sends test current through the cable under test. It's no-nonsense design gets the job done.

Martin Rowe covers test and measurement for EDN and EE Times. Contact him at Follow me on TwitterVisit my LinkedIn page

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