How do I fix this "blown" pcb area?

What are the components on the other side?

I have seen motor controllers with a parallel groups of devices, say solid state switches (e.g., SCR's or mosfets) show that type of board failure when one fails shorted. I can't make out the typical 3-pin pattern on the reverse side you show, and I am not even guessing that is what the components on the other side are. But, there is a chance that if you show the other side, we may have some suggestions to save the board.

Otherwise, you could just keep soldering chunks of wire over every failure point until, eventually, the circuit fuse blows. The board still won't be working, though.

John

 

Sorry, but I do not recognize what appear to be the critical parts. Someone else may.

As a word of caution, some of the capacitors have fairly high voltage ratings (e.g., 850V and 400V) as well as capacitances. They can give you a pretty good shock and may not be fully discharged when you remove the board, so be careful. After disconnecting the mains power to the board, you would want to use a resistor to short across the leads to discharge them. Anything rated at less than 50V won't give much of a shock.

John

 

Do the black tombstones next to the inductor/transformer coil have any markings on them? They are physically close to the failure points.

John

 

They look like AC capacitors. I wonder if one or both failed, which is causing the over current. Since they are at the mains input, they are probably to prevent interference from the unit getting back into the mains.

I haven't read this article (I am cooking dinner), but the circuit shown is certainly consistent with what I see on your board.

http://www.acoustica.org.uk/other/filter.html

You will need to remove them to test them. Do you have access to a smaller soldering iron? Do you have solder braid to remove the solder? I hate to suggest what I do, because I will get jumped on. When I don't have solder braid (which is very rare), I melt the solder and flick the boards over a shop waste basket. That gets enough solder off to wiggle the parts -- maybe with a little more heat -- and eventually get them out without damage to the part or the board.

John

 

Usually if the fuse is the correct current rating and type, if it doesn't blow the problem causing the high current (probably a short between phase and neutral) is before the fuse in the circuit. Towards the input connections from the fuse.
Did you try a Google search for a circuit diagram, it might help a little, no guarantees though.

 

Many years ago, I learned that Sutton's Law* is rarely violated. The capacitors are near the problem and can fail short, but that doesn't explain why you get failure only under load. Nevertheless, they are simple to test. That is why I mention them. If those capacitor are OK, then the problem is downstream and the PCB traces near the capacitors were only the weakest link.

If the circuit to which I posted a link is reasonably representative for what you have, then a short test without the capacitors in circuit (after repairing the newly burnt out trace) should produce minimal harm to the "grid". I think your chance of success is relatively small, but it is not nil. Is there any way you can substitute a smaller mains fuse or maybe test the circuit in series with an incandescent light bulb to limit the current draw in the event of a short circuit?

John



*After Willie Sutton, a bank robber.

 

One rectangular block block is labelled CP24 so is probably a capacitor in the power section.

The printed circuit track could be linked with a strand of thin wire. Most flexible cables are made with wire of thickness 0.0076 in or 0.2mm. This has a fusing current of about 6A so you could use this to lonk the track. What is the fuse rating fitted?

If there is a lot of solder, I use a solder sucker to remove most of it and then use braid to clean up further. If you do not have the braid, you can use braid from coaxial cable. It needs to be free of corrosion and could be smeared with a very small of flux to aid wetting.

I am not skilled enough to use a solder gun to get the right temperature.

Edit
If the circuit blows instantly presumably the power is switched before the board, not in the board.