Transformer Giving Out Double The Voltage

[garrymc123]

I HAVE A TRANFORMER OUT OF A KAM LASER LIGHT THAT WENT FAULTY. IT JUST WENT DEAD SO I REMOVED THE TRANSFORMER AND FOUND A JUMPER WIRE BURNT OUT SO I REPLACED IT WITH ANOTHER ONE BUT NOW THE OUTPUT VOLTAGE HAS DOUBLED FROM 12V TO 24V WHAT WOULD CAUSE THIS SORT OF PROBLEM WHAT DO I TEST/CHECK

PS I HAVE ANOTHER LASER TRANSFORMER THE SAME AS THIS ONE BUT IT IS DEAD I HAVE CHECKED THE GLASS FUSE WHICH I REMOVED AND CHECKED AND IT IS OK AND IDEAS WHICH ITEMS TO CHECK IS APPRECIATED


CHEERS

HERE ARE SOME PICS

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[Radio Fox]

Are you sure it was just a jumper wire? They are normally quite thick & will take a lot of current to burn one up. What was the board marking for the jumper?

[garrymc123]

it was just a straight line bellow the burnt wire i put the new wire on the bottom side because it was to tight at the top her is a pic

cheers radio fox for info

[Krankshaft]

If the 24 volts is stable check the components in the feedback loop of the PWM.

[stj]

a gas laser is like a flouro-lamp,
it needs an initial strike voltage followed by a lower running voltage.
maybe it's stuck in "ignition" mode.

unless it's a solid-state diode-laser.

whatever it is, unless it's bad soldering it's probably gonna be a bitch without a schematic.

[Krankshaft]

A burned trace is due to an over current condition are you sure that the laser it's driving is fine?

Confused me there the proper term for this board is a ballast board.

[garrymc123]

sorry folks i haven't explained the problem properly the power board is from a animation laser there is two outputs from the transformer board the twelve volt output controls the dmx board and the motors for the mirrors. then there is a 5v output for the laser itself which when tested gave 5v its the 12volt that has doubled to 24v is it the yellow tranformer on power board that drops the voltage from 240v to 12v and 5v could this be faulty i think it is a smps but no data on the yellow thing to tell me voltages or make model her is a pic hope this helps thanks again.

[garrymc123]

what is this yellow thing called and what does it do

cheers.

[stj]

that's the transformer.
what's the part number on the part stuck to the black aluminium cooler on the right?

[Dgtech]

That's gotta be a typo (240V). If the voltage you see on the primary of the transformer is 24 volts and the secondary has 12 volts then that could be right depending on the transformer's job. If it is supposed to step down the voltage so that the secondary could have higher current, then it most likely is fine.
Not knowing the circuit, is there any way the transformer could have been placed in backwards - causing a step up?
A transformer is a ratio device so a 2:1 could be put in backwards to produce 1:2.

[Krankshaft]

The 5 volts looks like it may be externally regulated on that outlying board.

A switching transformer has a fixed turns ratio to reduce a certain primary voltage to a certain secondary voltage this can't change. The only way this could happen is if the PWM feedback is off increasing voltage to the primary.

Get the datasheet for the 4 pin PWM IC and check the external feedback components.

Unless of course the switching transformer was reversed as posted above.

[garrymc123]

the thing with the black heatsink on the right is a n channel mosfet part no
FQRF 5n60

[stj]

makes sense,
have you removed the board from the metal frame and checked the soldering?

[garrymc123]

yes have removed board and checked soldering i have swoped the foiling items the yellow transformer,n channel mossfet ,the 3 rectifier diodes at the back with the metal silver heatsink across them and also the ic chip but still getting 24v instead of 12v i think i will change the black diodes and see if that helps and

any info appreciated cheers

[Dgtech]

I need to look up some info on this before you go too far. There is a systematic way to troubleshoot. Switching parts to try to find the bad one doesnt work most of the time. It just causes more problems. What is the exact name and model number for the whole device?

[skystormfarms]

?

[Jack Crow]

Guys,
Are we not missing something?
That beastie in the photo is a switcher not a linear.
At the frequency it's cranking there are very few home meters that can measure the AC output of that thing (aprox 50khz), let alone the square waves.

Another thing judging by your choice of words, your in the UK or a similar 220vac mains country.

Garry, these things can be a hazard to work with if you are not well equipped.
Im talking line isolation transformers, variacs, all that stuff.
It is plugged into the 'mains' of your building. Bad thing to get between that much voltage and current, to anything that smells like a ground. 220 may be more efficent but it's a better killer as well.

Few things to check with switchers.

First is they must be tested under load.
Don't run it into your laser, they tend to be expensive to replace.

Since your system is a solid state laser unit, good chance the regulated output is the +5 volt. So isolate the P/S from the rest and hang a load on there good for about a half amp. Let's say a ten ohm about ten watts, over kill for sure.

See if the rest of the outputs come into line when +5 is loaded.
If that's the case, your laser may have been popped for some reason, and is not placing the correct load on the P/S giving you the wrong impression about what is working and what is lying to you.

All the other outputs are in ratio to the 5 volt regulated control signal. So if the +5 is high, so will the others.
Welcome to the world of consumer electronics.
If it's cheap, and it works, it ships.
Yeech.

Hope this helps.
Mike aka Jack Crow in Herndon VA

[momaka]

Originally Posted by Jack Crow

All the other outputs are in ratio to the 5 volt regulated control signal. So if the +5 is high, so will the others.

I saw a circuit like that before in the PSU of a LCD monitor I fixed. You can get some amazing voltages on the other rails when the 5v falls out of regulation.

Originally Posted by skystormfarms

?

Dude! If you're going to dig up and old thread, at least have something more meaningful to say.
I wonder what happened to the minimum character limit - should have caught this.

[Agent24]

Probably a spammer or something