New Blue2 Ring Tester is now available. Click here for details.
The original LOPT / FBT Tester Page.....
This is the Dick Smith Electronics K7205 kit
They no longer make any kits
Click to download the complete K7205 kit notes as an Adobe
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.
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
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
* Also useful for testing deflection yokes and switching power supply
* No fiddling with 'threshold' controls etc; readout is a clear
* Kit instructions contain a huge amount of information and hints for
tester and diagnosing horizontal deflection stage
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.
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Last update: 06 Mar 2020