crt flyback transformer testing - Page 1
Forum section: electronics / beginners

author: Rerouter
author_rank: Super Contributor
timestamp: June 03, 2013, 10:50:01 am
content: Over the past few months when I find a few free minutes I've been repairing an old data precision 6000 spectrum analyserSo far I am up to the main 5v high current power supply/ CRT high voltage supply PCB, I have had to replace a number of parts specific to the 5v section but when I reached the CRT part for testing both the primary and secondary seem open circuitThere are only 4 connections to it, switcher in, CRT out, a pin labelled R and a pin labelled G connected to groundNow below I have attached an image of the offending flyback and am left wondering if short of in circuit testing, if there are some basic tests I can run on the thing or if it is fried if anyone has thoughts on how it can be replaced, if needed I can draw out the schematic of what drives it...

author: Psi
author_rank: Super Contributor
timestamp: June 03, 2013, 12:35:22 pm
content: Pretty sure it's only the voltage multiplier (tripler)If it had a flyback transformer inside as well i would have expected more pins.

author: Paul Price
author_rank: Super Contributor
timestamp: June 03, 2013, 12:39:17 pm
content: What you seem to show is not a flyback transformer, but what a flyback transformer connects to, a high voltage multiplier diode and capacitor assembly that converts some lower high frequency, high voltage AC voltage from a flyback circuit (about 3kV AC pulses in, 7000 to 12000 DC out). You can test it by feeding putting into the circuit it came from, it it develops the DC HV it is supposed to, then it is ok. If it instead gets hot, arcs over, or seems to otherwise overloads the pulsed transformer circuit that connects to it, then it is not ok.To test this device, you can create a circuit sometimes known as a Polish Inverter. Create a flyback circuit by borrowing a spark coil from your neighbor's car. Connect one side of the coil to a 1.5V power supply. Connect the other side to a .1uf/600V capacitor to ground. Now from the junction of the capacitor and the coil, connect an alligator clip lead to a large bastard file with sharp horizontal ridges. Now, take a second alligator clip lead and connect one side to ground and the other to a small screwdriver shaft. By rubbing the screwdriver lightly and rapidly along the ridges of the file, you will create a very fast switching circuit that should produce several thousand volt pulses from the spark plug side of the coil connected to the voltage multiplier input pin under test. You should then detect a 9000V to 15000V DC presence at the anode connector output.Watch out for shocks.

author: Psi
author_rank: Super Contributor
timestamp: June 03, 2013, 12:44:09 pm
content: Here's a picture of a flyback and tripler working together

author: smashedProton
author_rank: Frequent Contributor
timestamp: June 04, 2013, 07:20:33 am
content: How many days without posts from rerouter,would it be until it is safe to assume he is dead? Sereously dude, try not to mess with forces you don't control.

author: Rerouter
author_rank: Super Contributor
timestamp: June 04, 2013, 12:16:20 pm
content: Quote from: smashedProton on June 04, 2013, 07:20:33 ami'm not trying to mess with what i do not understand, it was a case of this thing came to me non functioning, as such i'm testing every component to find any that have failed or gone out of spec, and either replaced or made note of them, the crt not turning on was one of the problems, so i figured the fly-back may be a simple transformer and upon measuring albeit rare both the windings may have been cooked, though to be fair i do not know much control theory on high voltage fly-back supplies, just the theory of how they operate,(thanks very much psi and paul,)being a doubler and not a transformer is good news for me, as it means it cannot really go blowing out the tube which is my greatest concern,

author: Psi
author_rank: Super Contributor
timestamp: June 04, 2013, 12:44:35 pm
content: Here's some useful tripler info and pin-outs (voltages are probably for a TV rather than a scope)IN - from flyback (6-10 KV AC).OUT - HV to CRT (20-30 KV DC).F - focus to CRT (2-8 KV).CTL - focus pot (many megohm to ground).G, GND, or COM - ground.Symptoms of tripler failure are: lack of high voltage or insufficient highvoltage, arcing at focus protection spark gap, incorrect focus voltage, otherarcing, overload of HOT and/or flyback, or focus adjustment affectingbrightness (screen) setting or vice-versa.