LOPT / FBT Tester Page!

This is the Dick Smith Electronics K7205 kit

They no longer make any kits


Download the complete K7205 kit notes as an Adobe Acrobat file! (370KB)
For Netscape users, right click here and select 'Save Link As...'
For Internet Explorer users, right click here and select 'Save Target As...'
Then save the k7205.pdf file to an appropriate subdirectory on your hard drive.

Many thanks to Bill De Rose at Dick Smith Electronics for providing these kit notes!

Right-click here to download the Espaņol translation of the kit notes as a 260KB zip file

A big "GRACIAS!!" to Fernando Flores Bonilla for making this available.

You need Adobe Acrobat Reader to view this file, so if you don't already have it, click on the logo and download it for free.


This little instrument identifies faults in horizontal output stages by doing a 'ring' test, i.e. it applies pulses to the LOPT / FBT primary circuit, and counts the number of damped oscillations or 'rings' produced. For each 'ring' down to about 15% of the test pulse amplitude, one LED in the 'bargraph' lights up... nearly all faults will greatly reduce the number of 'rings' and give a very low reading.

It can be used on both monitors and TVs because it's not frequency-sensitive, and the test signal amplitude is only 650mV- low enough not to forward-bias semiconductors in the circuit.

To do a basic test, you connect the test leads between chassis and the HOT collector... if more than 4 LEDs illuminate, the horizontal output stage is probably OK. It can check LOPTs / FBTs out of circuit if broken-down components prevent an in-circuit test.

It can't show up breakdowns which only occur at full operating voltage, and it has no facility for measuring EHT voltages etc... but then again it only costs a tiny fraction of the price of instruments that can! In general it will show up about 80% of failures in horizontal output stages, and is also useful for checking deflection yokes, switching power supply transformers and other high-frequency high-Q inductive components.

Brief Specifications

Measurement range: 0 to 8+ 'rings' of inductor/transformer under test
Peak test voltage: 650mV
Power supply: 6V DC (4 x 'AAA' cells)
Controls: Push on/push off power switch
Dimensions: 2.7 x 5.2 x 2.2 inches (69 x 132 x 56mm)


* Can generally test LOPT/FBTs in circuit, if no other components are faulty.
* Also useful for testing deflection yokes and switching power supply transformers.
* No fiddling with 'threshold' controls etc; readout is a clear 'bargraph' display.
* Kit instructions contain a huge amount of information and hints for using the
  tester and diagnosing horizontal deflection stage faults.

Feel like building your own?

It's not hard. Use 5mm LEDs and simply drill holes into the box lid for them. Download the PCB positive artwork as a .pdf file by right-clicking here. You can print this onto transparency film with a laser printer, but first print it onto paper and make certain that the board dimensions are exactly 2.0 x 3.0 inches. Adjust your printer settings if necessary.

To use the toner transfer method, right-click here to download the mirror-image version of the artwork. "Thank you!" to KzCorp for making this file available. As above, make certain that the printout is 2.0 x 3.0 inches before you make a board from it.

The new successor to the Dick Smith kit

This is the Blue Ring Tester kit from Anatek Corp in the USA, based on my K7205 design.

All the information you need is on the Alltronics website. Click here to go there!


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Last update: 25th October, 2018