3.1v on CPU socket Pin 2

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t120r
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3.1v on CPU socket Pin 2

Post by t120r » Sat Nov 02, 2019 9:56 pm

So I was doing the tests ad I'm getting 3.1v on pin 2 of the cpu socket (CPU not installed). This doesn't make sense as it's a straight run to pin 1 according to the schematic.

jbelanger
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Re: 3.1v on CPU socket Pin 2

Post by jbelanger » Thu Nov 07, 2019 10:47 pm

You're not reading the schematic correctly as pin 1 and pin 2 are not connected together.

Jean
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t120r
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Re: 3.1v on CPU socket Pin 2

Post by t120r » Fri Nov 08, 2019 12:25 am

What I had was the following voltages on the CPU socket: Pin 1 = 3.29v, Pin 2 = 3.10v, Pin 3 = 3.29v. What I found was the board was shorted in this area. I'm not sure how, but I must have overheated it. According to the schematic, Pin 2 should not be connected to anything, just goes to pin 1 of the BDM header.

jbelanger
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Re: 3.1v on CPU socket Pin 2

Post by jbelanger » Fri Nov 08, 2019 1:24 am

Is it possible that you have too much solder which has shorted pin 2 to either one of the other pins on the socket? It's easy to see on the bottom of the board but pretty much impossible to see if that happens under the socket.

You might want to try to use solder wick to remove some solder on pin 2 but be careful not to overheat the board. It's not a big deal if you lose connection between the BDM header and pin 2 so heating that pad should not be an issue.

You can try to see if you have a problem when you put the CPU in place. The worse that could happen is that it won't give you an RPM output. If that's the case and you can't get anywhere with solder wick, you can always bend pin 2 on the CPU just enough so that it doesn't go in the socket. That will have the same effect as no connection.

Jean
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t120r
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Re: 3.1v on CPU socket Pin 2

Post by t120r » Fri Nov 08, 2019 11:51 pm

Thanks for the suggestions. I'm going to pick up some solder wick.

t120r
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Re: 3.1v on CPU socket Pin 2

Post by t120r » Sun Nov 17, 2019 11:39 am

So i used the solder wick in conjunction with my solder sucker to transfer my components to the new board i bought from you. Pins 1 and 3 are 3.29v and pin 2 is now 0v. So that's that problem sorted.
I do have negative voltage of -1.18v on pins 15 and 16 though. It was there with mý old board as well. I wonder did i cook Q1 or Q2 ???

jbelanger
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Re: 3.1v on CPU socket Pin 2

Post by jbelanger » Sun Nov 17, 2019 1:48 pm

There is no way to actually have negative voltage on the board so there is something not quite right with the way you are taking the measurement. Having said that, the only way you can have voltage on those pins if there is something bad with Q1 and Q2, is if you have installed the pull up jumpers. If there is a short on Q1 and Q2, either through a failure or a solder short, then you could see the voltage from the pull up. And depending on how you take the measurement, that could show as a negative voltage.

Jean
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t120r
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Re: 3.1v on CPU socket Pin 2

Post by t120r » Sun Nov 17, 2019 7:59 pm

Well my negative lead is attached to the ground header pins. Pins 1 and 3 have +3.29v. Move the same probe to pin 16 and it inverts to a negative voltage. There are no jumpers installed.

I agree it makes no sense. I'm going to replace Q1 and Q2 on spec anyway. See what the change is. In another post i asked you about the 2nd trigger staying dimly lit but still flashing. A bad transistor could probably be doing that.

jbelanger
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Re: 3.1v on CPU socket Pin 2

Post by jbelanger » Sun Nov 17, 2019 9:59 pm

Since you're going to replace Q1 and Q2, check the voltage on pins 15 and 16 after removing the current transistors and before putting the new ones in. And check that they are not connected to anything (ground or 3.3V). And check that R21 and R24 are only connected to pins 15 and 16, respectively, and only one pad on Q1 and Q2. You should also check the other pads on Q1 and Q2 to make sure there are no shorts and they are connected to the correct places.

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t120r
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Re: 3.1v on CPU socket Pin 2

Post by t120r » Thu Nov 21, 2019 8:55 am

So i removed Q1 and Q2 and everything checks fine. Put in new ones and still get -1.4v on pins 15 & 16 of the CPU. These are the only abnormal readings i get. I put the cpu in anyway and everything works fine. I have a good trigger pattern on tuner studio. I used to have a problem with the 2nd trigger keeping the led dimly lit during the tach tests, that's gone now. I'll just chaulk up those negative voltages to my Fluke meter not liking transistors. As long as my MS3X gets the proper tach signal, I'm happy.

Still can't upload my wheel pattern though. I'll save that for another day.

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