Blog
How to use the Tesmen TLP 900A/R network cable tester (toner, PoE, crimp check)
Short answer: hold the power button for a few seconds to turn the Tesmen TLP 900A/R on, then pick a function: scan (cable test), toner, or both at once. It also has a TEL port for phone lines, a PoE port that tells you if power is present, a crimp check where you just plug in one end of a patch cord, a flashlight and a non-contact voltage (NCV) detector. It works well for testing cables; the NCV is not reliable and there is no auto shut-off, so the 9 V battery can drain.
Why I made this guide
When I looked for help on this tester, Tesmen's YouTube channel had no video about it, at least as of 2026. So if you bought this model, or you have one and don't know what all these buttons do, here is how I use it step by step.
Power on, scan and toner modes
Push the power button for a few seconds and the unit turns on. The functions are printed on the front:
- Scan: tests a cable such as a patch cord.
- Toner: sends a tone so you can trace a cable with the probe.
- Both at once: you can run the toner and the scan at the same time. I'm not sure when you need both, but the option is there.
There are two jacks: the RJ11 port for 4-wire phone lines and the RJ45 port for data cables. To test a long patch cord (for example 50 m / 100 ft), plug one end into the main unit and the other into the remote unit; you don't have to turn the remote on and off, it just works.
TEL port: checking a phone line or PBX
The port marked TEL is for telephone lines, such as a landline or a PBX, and the kit includes a cable to connect it. I didn't have a landline to test, but according to the manual the LED tells you the line status: green when there is just a line, blinking between green and red when the phone is ringing, and another color if the phone was left off the hook. It also shows the polarity of pins 3 and 4 with different colors for positive and negative. Personally, I would prefer separate LEDs for ringing, polarity and off-hook so it's easier to read.
PoE detection and the crimp check
PoE: plug a Power over Ethernet cable into the PoE port and the tester tells you whether power is present or not.
Crimp check: this is a nice feature. Plug one end of a patch cord all the way in; the other end doesn't need to be connected to anything. If all the lights come on, the crimp is good. If some lights stay off (in the video port 1 and others don't light when the plug isn't fully in), the connector wasn't crimped properly or isn't seated all the way.
Flashlight and NCV voltage detector
The flashlight has to be switched on before you use it. It works, but I always carry a real flashlight, which to me is much better; still, if you have nothing else, it can be useful.
The NCV (non-contact voltage) function is meant to detect voltage without stripping the wire. You turn it on and hold it against something like an extension cord or power cord. In my tests it was not reliable: sometimes it detected voltage, sometimes not, depending on how I turned the cable. I have a $5 one from Harbor Freight that works every time.
Downsides: no auto shut-off and the battery
The main downside I see is that I couldn't find any auto shut-off. If you leave the toner on for hours, the battery will deplete and die. I have another similar tester that I like more because the toner only works while you hold a button and turns off when you release it, so you can leave the volume at maximum. With this one, carry spare batteries.
It comes with a 9 V battery from a knockoff brand I don't know. Cheap batteries like that can leak or rust the contacts inside, so I'd replace it. Another tester I bought came with a Duracell, which is the better choice.
Frequently asked questions
How do I turn on the Tesmen TLP 900A/R?
Hold the power button for a few seconds until it turns on, then select scan, toner or both.
Can it check a crimp without the other end connected?
Yes. Plug one end of the patch cord all the way in; if all the lights come on the crimp is good, and missing lights point to a bad or incomplete crimp.
Does it detect PoE?
Yes. Plug the cable into the PoE port and it tells you whether power over Ethernet is present.
Is the NCV voltage detector reliable?
Not in my tests. It detected voltage only some of the time depending on how the cable was turned; a cheap dedicated detector worked better.