Grounded signal lines

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Grounded signal lines

Postby kbhayes » Sat Dec 20, 2014 10:06 pm

I have a 2.0.1 board that I have been building slowly. The board was completed and I was at the point of doing the testing before installing in the case. I had 12v at the power point. i had 5v at the test point. Then I tried to test the signal lines with a led and a 12v source. When I tested line one, I got a lit led when I connected power to it without grounding the signal line from the ecu. Line two did the same thing. Lines three and four worked exactly as intended. I went looking for solder bridges, cleaned the board and removed any solder that seemed excess. The result was that line four was now grounded as well. Not sure where to go with it now, I tested some random points. Since the problem appeared to be with ground, I tested the ground. I found that the lines that had a problem were grounded (had continuity with the ground test point).

The board is still loose, not in the case so grounding to the case is not possible at this point.

Any thoughts on where to go with this now?

As a side note, I need to replace the tip122's and tip426. I had mounted them the same way they are in the MS3. Got ahead of myself there. I am wondering if it would be a good idea to buy another bare board to move the chips to or at least to test against.

Thoughts?? (and thanks. I am impressed with how well these forums work.)
Ken
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Re: Grounded signal lines

Postby jbelanger » Sun Dec 21, 2014 2:26 pm

Replacing the TIP122 and TIP42C is not too difficult but moving the chips from one board to another is going to be quite difficult to do without damaging anything if you're not equipped and used to doing this.

You need to check that the all the diodes are the correct way in. Check that there is no solder bridge between the pins on the small transistors (Q6-9). Also, with power on check the voltage on pins 1 and 2 of each LM1949 chip; you should have less than 1V with nothing connected to the inputs. If you ground an input, you should have 5V on pin1 and more than 1V on pin 2.

Jean
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Re: Grounded signal lines

Postby kbhayes » Sun Dec 21, 2014 9:42 pm

Jean

Did the tests. All diodes are in right way round per the marks on the board and similar to the picture in the instructions. There are no bridges on Q6-9. I tested the pins for continuity and had no shorts. Nothing visual either. So with the power on, I had 4.96 volts on pin1 and 4.02 volts on pin 2 of the LM1949 for lines one and two with nothing grounded. I got the reading as soon as I hitched up. Did not try it grounded. The tip122's are removed from 3 and 4 so I couldn't test them. They gave readings, but they were strange. (floating)

Thoughts?
Again thanks
Ken
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Re: Grounded signal lines

Postby jbelanger » Sun Dec 21, 2014 10:42 pm

Check what voltage you have on the middle pin of Q6 and Q7 (you can use the pads on R14 and R15 closest to the transistor since it is connected to the middle pin).

I suspect that Q6 and Q7 might be damaged which is why you get 5V at pin 1 of the LM1949 regardless of the input. It is possible to burn these if you apply too much heat when soldering them in place.

Jean
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Re: Grounded signal lines

Postby kbhayes » Tue Dec 23, 2014 9:31 pm

I have 5v on the middle pin of Q6,7 & 9. I have 3.6v on Q8.
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Re: Grounded signal lines

Postby jbelanger » Tue Dec 23, 2014 10:03 pm

That sounds like you might well have damaged transistors. Normally, you should have about 0.7V on the middle pin and about 0V on the third pin which is connected to pin 1 of the LM1949. If you ground the input, you should have 0V on the middle pin and 5V on the third pin.

The 0.7V is the voltage on the middle pin when the transistor is on and that connects pins 1 and 3 and since pin 3 is connected to ground that means pin 3 should also be 0V which is also what you should have on the LM1949 pin 1.

The other possibility I can think of is that the middle pin is not correctly soldered. With a correctly soldered and undamaged transistor, you should never see more than about 1V on the middle pin. Anything higher means that you either have a damaged transistor or a bad solder joint.

Jean
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Re: Grounded signal lines

Postby kbhayes » Fri Dec 26, 2014 7:23 pm

Jean

I have 0v, 5v and 5v on lines 1 and 2. With the TIP122's uninstalled on 3 and 4, I took no readings.
So, yes, I think the transistors are toast. I have removed the Tip122's, Tip42c and Q6-9. I have ordered some replacement chips. I will post again when I get it back together. I cleaned the board up generally and the sockets for those chips, so I am ready to reinstall them.

Thanks for the help
Ken
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Re: Grounded signal lines

Postby kbhayes » Sun Mar 29, 2015 8:28 pm

Jean

Back at it again.
I decided to build the third board yesterday. All went well. I had 12v and 5v when finished. I connected the signal lines, driver lines and individual grounds one at a time to check it out. I did #1 and got a lit led when I grounded the line as per test instructions. The same went for #2 and #3. When I did #4, it also worked for a moment. Then I tried connecting all the ground together to test the lines in sequence. When I connected the grounds, something happened. I had a lit led with no signal lines grounded. I had mounted the LM1949 in sockets, so I pulled the chips from #3 and #4. I tested pins 1 and 2 of both sockets. #3 had minimal floating voltage. #4 had 3.3v on #1 and minimal on #2. I changed Q9, but messed up the pads in the process. I now have the led 1/4 lit with no lines grounded. From our previous dialog, I think I need to look at the TIP122's?? But what would have made them fry?? The power supply I am using is 12.3 volt. I have used it with the sim cards for the MS with no problems.

Thoughts?

Thanks
Ken
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