# Duo phase diode mishap



## chongmagic (Feb 17, 2019)

I got in a hurry and lifted the solder pad on the anode of D1A. Is there any chance of salvaging the PCB at this point? Looks like it connects to pin 8 of three different TL074s.


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## Robert (Feb 18, 2019)

Yes, it's not the end of the world, it can be salvaged.    

Reinstall the diode, bend the lead over and solder it to the right end of the 4K7 resistor just above it.
Make sure there is continuity between the three red pads in the pic below.   If there isn't, install a jumper wire accordingly.


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## chongmagic (Feb 18, 2019)

Weird I have connectivity with the 4k7 and 4148 but nothing to pin 8 of the IC. I would think if the pad was completely damanged I wouldn't have the connectivity between 4k7 and 4148


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## Robert (Feb 18, 2019)

It's through-hole plated so the 4K7 / 4148 are probably making connection on the top side of the board.


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## chongmagic (Feb 18, 2019)

Ok I've got continuity for all three pads. I tested the anode side on the other side for the 4148 and it is around 8.5v but on the anode of D1A I'm only getting several mv. I think something is still awry. I haven't connected any 3pdt yet and just connected it to 9vdc. And the lights for the LDRs aren't even coming on. The ICs are close in voltage on both sides of the board, I am guessing they are mirrors of each other and should be close voltage wise.


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## Robert (Feb 18, 2019)

What voltage do you have on pin 1 & 8 of IC7A? (the charge pump right beside D1A)


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## chongmagic (Feb 18, 2019)

Right now there is a short somewhere.









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						New item by Jonathan Freeman
					






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## chongmagic (Feb 18, 2019)

I don't see any bridged connections not sure what is causing the short.


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## Robert (Feb 18, 2019)

What point is shorted?  And where is it shorted to? Ground?


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## chongmagic (Feb 18, 2019)

When I plug up the positive and negative to my test box it seems to cause a short back to the power supply. It causes the LED on the power supply to turn red until I unplug it. Not sure where it is stemming from. Maybe the solder pad I damaged is causing the issue. I think it must be shorted to ground


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## chongmagic (Feb 19, 2019)

Yes the anode side of D1A is going to ground but so is pin 8 of IC7A. It has to be stemming from there. But I see the the anode side of D1B is doing the same.


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## Robert (Feb 19, 2019)

Those points are all connected together, so a short on one will show up across all of them.

Pull the charge pumps and opamps one at a time and see if you can locate the short that way.


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## chongmagic (Feb 19, 2019)

Yeah the short is still there with all the opamps and charge pumps removed. I think this PCB is toast but I learned a good lesson, patience is the key.


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## Robert (Feb 19, 2019)

I would look very closely around where the pad lifted, if it's not one of the ICs there must be a short to the ground plane.


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## chongmagic (Feb 19, 2019)

Is the ground plane in the middle of the PCB?


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## chongmagic (Feb 19, 2019)

Is pin 3 of the charge pump ground as well?


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## Robert (Feb 19, 2019)

No, there are no internal layers, only top and bottom.

Yep, pin 3 of the charge pumps go to ground.


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## chongmagic (Feb 19, 2019)

Here is a close up of where the pad lifted and the jumper to pin 8.









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## chongmagic (Feb 19, 2019)

Maybe I should try removing the jumper.


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## Robert (Feb 19, 2019)

Remove the diode and jumper and clean the solder from around the area and see if the short goes away.


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## chongmagic (Feb 19, 2019)

The short remains.


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## zgrav (Feb 20, 2019)

while you have the ICs pulled, check to see if any of those pin holes are connecting to ground where they should not be.  might help you isolate the problem part of the circuit.


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