Help with MBP 3PDT-05 with LED always on

[dchang0]

Hi, everyone--

First time poster.

I have a MBP 3PDT-05 PCB that has the LED always on.

The IN/OUT bypass works as it should, but the pole for the 3PDT switch that is supposed to disconnect or connect the LED's negative leg to ground doesn't work. All three pins in that one pole are always measuring continuity with each other. The other two poles flip back and forth between throws properly.

It's as if the 3PDT switch has one shorted-out pole inside itself.

However, this is unlikely, as the 3PDT switch probably doesn't have a metal slider inside that is long enough to touch all three pins of that pole at once. Also, if the metal slider inside were stuck, it would probably block the switch from operating, since they are mechanically linked.

What is more likely is that there is some short to ground on the PCB, possibly from bad soldering, so that the LED's negative leg is always grounded, thus making the three pins of that pole of the 3PDT switch always seem to be shorted to each other, even though they are really shorted via some joint outside of the switch.

Has anyone else seen this problem before?

I am asking first before I attempt to remove the 3PDT switch from the board, which will be a massively difficult operation due to having to desolder 9 pins all at once. If I removed the 3PDT switch entirely, it would be very easy to determine where the fault lies, as I could measure the switch's continuity itself and measure the PCB's continuity itself. But it would likely mean using a heat gun to heat all 9 pins at once, which probably will damage/melt something.

I'm hoping that someone has seen this problem before and can guide me to where the problem is before I have to take the switch out. If I'm lucky, it's something as simple as a bad soldering short to ground somewhere else on the 3PDT-05 PCB that can be cleared easily. My solder joints look good (I've been soldering semi-professionally for decades), but I can make mistakes.

For now, I have removed the LED, hoping that it might have been where the short to ground was happening, but no luck there.

Thanks very much in advance!


UPDATE:

I figured it out.

I began to suspect that the short was under the 3PDT switch, so I sucked out some of the solder from those three pins.
Also, I figured out that two of the pins are always in continuity as specified in the schematic, so what really matters is continuity between the square solder pad and the center pin of that throw.

This question is now moot, but please leave it here to help someone else in the future.

[jimilee]

Hi, everyone--

First time poster.

I have a MBP 3PDT-05 PCB that has the LED always on.

The IN/OUT bypass works as it should, but the pole for the 3PDT switch that is supposed to disconnect or connect the LED's negative leg to ground doesn't work. All three pins in that one pole are always measuring continuity with each other. The other two poles flip back and forth between throws properly.

It's as if the 3PDT switch has one shorted-out pole inside itself.

However, this is unlikely, as the 3PDT switch probably doesn't have a metal slider inside that is long enough to touch all three pins of that pole at once. Also, if the metal slider inside were stuck, it would probably block the switch from operating, since they are mechanically linked.

What is more likely is that there is some short to ground on the PCB, possibly from bad soldering, so that the LED's negative leg is always grounded, thus making the three pins of that pole of the 3PDT switch always seem to be shorted to each other, even though they are really shorted via some joint outside of the switch.

Has anyone else seen this problem before?

I am asking first before I attempt to remove the 3PDT switch from the board, which will be a massively difficult operation due to having to desolder 9 pins all at once. If I removed the 3PDT switch entirely, it would be very easy to determine where the fault lies, as I could measure the switch's continuity itself and measure the PCB's continuity itself. But it would likely mean using a heat gun to heat all 9 pins at once, which probably will damage/melt something.

I'm hoping that someone has seen this problem before and can guide me to where the problem is before I have to take the switch out. If I'm lucky, it's something as simple as a bad soldering short to ground somewhere else on the 3PDT-05 PCB that can be cleared easily. My solder joints look good (I've been soldering semi-professionally for decades), but I can make mistakes.

For now, I have removed the LED, hoping that it might have been where the short to ground was happening, but no luck there.

Thanks very much in advance!


UPDATE:

I figured it out.

I began to suspect that the short was under the 3PDT switch, so I sucked out some of the solder from those three pins.
Also, I figured out that two of the pins are always in continuity as specified in the schematic, so what really matters is continuity between the square solder pad and the center pin of that throw.

This question is now moot, but please leave it here to help someone else in the future.

Nice job. Sometimes it helps to talk it out.


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