Subwoofer amplifier PCB repair

From the translator: translation of the repair history of the PCB. Carefully, under the cut 3 MB photos.

That was how the amplifier looked after it was removed from the case. Pay attention to swollen capacitors (which was the cause of the breakdown). These electrolytic non-polarized capacitors spread over the board, hit the tracks, caused a short circuit and caused ignition. When the board was charred, it began to conduct even more current, and burned even more - as a result, everything broke, there was a lot of smoke and there was a terrible stench.


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You can clearly see the mark on the radiator and the body, where there was a fire. The size of the radiator is small, because CLASS-D amplifiers usually work with high efficiency and do not generate much heat (compared to the efficiency of 30-40% of class AB amplifiers).



The photo shows the bottom of the board after a long cleaning (with a solvent and a toothbrush) before removing any components. Sucks, agree. Most would have thrown her in the trash. But I like the challenges, and I do not belong to the majority.



Top view after removing components. For this, we had to cut the glue that held it all together with a clerical knife, without damaging the components, especially the enamel on large toroid inductors.



View from a different angle. Horror!



We start to clean off the charred area of ​​the board. If we measure the resistance in this part, there will be only a few clods. Very very bad.



We continue to clean. In the center of the hole, where the damage is most serious, the burnt part broke as coals.



View from above



Peeled edges. It is necessary to remove all traces of charring.



Bottom (not yet ready).



Almost all coal is removed from the board. I checked all suspicious areas for resistance, just to be sure. The next step is to make a double-sided patch of the same thickness and the same copper. I used two-shell copper (0.203 mm) and FR4. If you are not sure, take copper thicker and measure the thickness of the board where there are no tracks. I had factory maintenance instructions, so I was able to do a little bit with Photoshop after exporting PDF.



Here are the data from the instructions to work. It is necessary to reduce everything to a black and white picture of the desired size and remove everything except the tracks.



Two layers, correctly aligned, one of them is made translucent to see both.



Then I scanned the board with a hole, made a gray transparent area in place of the hole. You need to align everything very accurately. I scanned the board with 600 DPI. The method of trial and error has achieved complete coincidence with the manual.



Using the gray area representing the hole, I determined the optimal location of the patch that would close the entire defect. All the pictures in Photoshop were divided into layers, here you see a JPG, with which it would be impossible to work - they are just for illustration.



Then he deleted all unnecessary information, left only the tracks and tags "top" and "bottom". Here all the layers are opaque.



We run in the Photoshop Threshold on each layer, so that wherever the color is, everything turns black and the rest is white. Here is the patch and is ready for printing. We go to the press.



I use such a press, some use laminators. It seems to me that the layers are easier to align on such a press. I use Press-N-Peel for making all the boards.



Now to the cutter. If you do this often, then this cutter is simply irreplaceable. First, we cut in rough, then we clean the edges on the grinding machine.



Top view on the printed patch.



Bottom view



Now we need to clear the hole, make good vertical cuts.



Now grind the patch so that it fits into the hole.



Final shape after neat pruning.



Perfectly included!



Everything is the same!



Everything coincides with the main board.



Last check backlit. Fine!



Now you need to remove the coating from the adjacent tracks for soldering.



Bottom view.



We start to connect. Connections are made with solder and wire. You need to try not to make large hills of solder so that they do not interfere with the components.



Bottom view. Here height is not so important, but still.



The final form of the patch with all connected tracks.



Bottom view



Since the board is double-sided, and the upper layer will not get close after installing the component, we use the grommets. They are soldered before assembly.



Bottom view. You can see a slight bulge eyelets. I have a bunch of grommets, but there is no press for them.



We begin the assembly. Hellish capacitors are replaced by polypropylene, they will not fail. It is quite difficult to place, spare parts are bigger. Legs have to do as short as possible. Why these parts were not in the original? Because the original parts were for a dollar thing, and these - for 12! Unhealthy appreciation. As always, the manufacturer needs the product to reach the end of the warranty period, that's all.



The final result. Everything is collected and working. For fastening used white double-sided tape 3M. Since This is a subwoofer, everything vibrates inside and you need to fix everything properly. I do not like glue, it is very difficult to make repairs with it. I was happy when everything worked the first time. Thanks for watching, I hope everyone enjoyed it.