DIY Cable Tester

We are all tired of fighting that intermittent connecting cable.

 So why not build a cable test box yourself?

It can be either quite involved or cover just the cables you typically use. Be sure to leave room for future expansion.

This is a general set of instructions, as there are many different cables, and listing how to build for specific ones is just too involved to list here.

Find a case style you like.

Install pairs of connectors for the types of cables you want to test. (BNC, F,  RCA, etc.)

Find a light bulb, say a 47 or 1847 and holder. 6.3 volts.

Wire up the connectors so one end goes to the power transformer, and the other connector goes to the lamp.

Add  2  fuses, line and output a power switch, and a pilot light. (I like to stick another fuse holder on carrying a spare fuse for ease of replacement if needed.)

For multi conductor cables, add a switch to select which wire in the bundle you want to test- like LAN cables.

The fuse is there to protect the power tx, and blow if the cable is shorted. 

In the case of coax or RCA cables, be sure to wiggle the cable ends in case you have an intermittent cable.

It is good to test known good cables so you will get an idea of how bright the light should be with a given length of cable, in case of a high resistance in the cable.

The reason for a pilot light that draws current is it will show up bad connections because of the current draw through the connector and cable.

If you use more than one pilot light for checking cable continuity be sure to use a filament transformer with large enough current capacity to handle all the bulbs, and change the transformer secondary fuse to match maximum expected current draw.

If you wire it up correctly, you will even be able to test cables that have different type ends on them, like a PL259 to BNC as an example.

Some of the commercially built units cost in the hundreds of dollars, where with a bit of scrounging or a good junk box it is quite possible to build a good tester for dirt cheap. 

Note: If you are building it to test multi-conductor cables, you may want to consider adding a bulb for each conductor- like mike cables- and a switch to check for shorts between wires in the cable.

         I built a similar box back in the 80's to test RS232 cables and with the rotary switch I used, and the way I set it up, I could even tell which wires were shorted to what other wire in a flat ribbon cable. (And yes, the factory that makes flat ribbon cables does have stray wires that can short completely across an entire 25 or 50 conductor ribbon cable ruining an entire 100 ft. roll of ribbon cable or a long run of it).