I am repairing a Delphi MT34 ECU, and after further investigation I came to a problem I couldn't understand or fix. After removing the triple regulator IC and all components in the track, the short is still there and it seems to be between the layers, I have never had such a problem and I don't know how to deal with it. The first picture is the top side and the second picture is the bottom side. How to find this short and how to fix it? There is literally nothing on that track until the resistor, and i removed the resistor, the track is very short, I have no idea what to do except scratching the tracks and try to remove the copper to block the track and test again. The short is between the two pins shown by the arrows, it is the lowest resistance i can find which is 0.7ohms. The pin with the resistor at the end of the track is the shorted one, and that track shorted to ground, the capacitor on the other pin is shorted, it seems to have failed, but the important track that outputs voltage from the regulator is P1.

Edit 1 : I tried shining a light as suggested nut it seems like that side is obstructed by something, on the top side between the P1 and P2 pins there is only one track coming from a ground, and the resistance is about 1.1, so i am not suspecting it.

Note : the burn mark in P1 track is just a marker i used, there is nothing wrong with the track

Note : the circle is there to define where both tracks end on the bottom side, I even removed the capacitor on P2, the P,1 track is very short snd doesn't go anywhere, already removed all components

Edit after Mr Dean pointed out it's a 4 layer PCB I tried to check continuity to the nearest capacitors, and found one to have continuity both ways but it's showing 0.7 ohm from P1 to this capacitor and 1.2ohm to the other side of the capacitor so I am doubting it, now it could be the culprit and it could be not, I will remove it later and see if the short will go away, if anyone has a better method of finding this short please inform me.

Top side

Bottom side

Top side showing the short points

Bottom side showing the short points, curcle indicates the track ends

enter image description here

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Large view of the section

  • \$\begingroup\$ Shine a light through from the other side of the board - can you see anything between the 'pins'? Show us photos of the board with the components removed. \$\endgroup\$ May 14 at 1:35
  • \$\begingroup\$ Tantalum caps like the one in the top photo can fail short. So can ic's for that matter. Like Bruce Abbot says, try shining a light through to see if it's really a 2 layer. \$\endgroup\$ May 14 at 2:01
  • \$\begingroup\$ If there is a tiny short in an inner ground layer from a whisker, a capacitor discharge of sufficient mJ energy should fuse open the short. Using a constant current DC across might work but not leave much margin in the gap. \$\endgroup\$ May 14 at 4:31
  • \$\begingroup\$ Added new pictures as requested, the most important track here is P1, but I don't understand why the light doesn't shine through, this also happens on other places in the PCB. \$\endgroup\$
    – ghost
    May 14 at 8:00
  • \$\begingroup\$ It sure looks like a 4 layer board, not 2. Those two pins also look like the are both connected to an internal plane (not necessarily the same plane). \$\endgroup\$ May 14 at 8:06


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