Trying to fix board with 2 switching circuits .

[SwitcherMaze90]

Hello everybody. I am new member i am a berber from morocco with a diploma in industrial electronics repair and really happy to discover this board.

Ok back to the problem . I have an electronic welder with a pcb containing two switching circuits .

The main one is a 4 igbt half bridge configuration driven by an oscillator.

The second one is an auxiliary power supply that gives power to the main chopper , cooling fan and startup relay. It is based on a uc 3842 oscillator (empty circuit in the picture).

Now as far as i can see the problem is in the auxiliary circuit :

1) There is no stable Vcc voltage only fluctuating from 12v to 14 v.

2) There is no output signal from the oscillator.

Here is a picture of the auxiliary circuit with uc3842 , transformer and mosfet removed :

 

[BradtheRad]

Surface thinking wonders if excessive current burnt up a component? It's easy to let a welding rod solidify to the work. We must act fast to prevent ruin. Because even though wise design normally puts circuit protection in place, the tendency is to minimize components in the welding loop since any extra resistance wastes power.

If you think the power supply is still good then I guess you want to build a substitute oscillating circuit to apply to the 4 igbt half-bridge.

Do you have a schematic for your unit? Can you locate a generic schematic for electronic welders?

 

[ZASto]

Who entered with the soldering iron i this board?
Lots of scorching marks on components (capacitors).

What is make and model of that welder?

 

[SwitcherMaze90]

If you think the power supply is still good then I guess you want to build a substitute oscillating circuit to apply to the 4 igbt half-bridge.

Thanks i think ill build a subsitute.

I cant find the original aux power supply fault i also powered up the vcc with external voltage " 15 vdc" and still no signal from the uc 3842.

 

[SwitcherMaze90]

Who entered with the soldering iron i this board?
Lots of scorching marks on components (capacitors).

What is make and model of that welder?

i bought this unit like that , its a chinese generic model with too many clones.

 

[ZASto]

Did you try to put new UC3842 and new MOSFET?
Consult datasheet of UC384x, there is a generic application circuit, and AFAIK chineese are very often sticking to it.

 

[SwitcherMaze90]

Did you try to put new UC3842 and new MOSFET?
Consult datasheet of UC384x, there is a generic application circuit, and AFAIK chineese are very often sticking to it.

Yes i have changed the uc3842 and the mosfet and still get a bad drive signal for the mosfet.

any toughts ?