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One problem I can't manage to fix


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Okay so I have assembled 6 boards in the past with no problems, then today I made a stupid mistake. Channels 5-8 weren't working. Well turns out I was rushing and accidentally had r1 and r16 switched, which I assume is what was causing the issue. I then desoldered them both and corrected that issue. Well long story short that didn't fix it. Checked all Solder joints, rest of the board works perfect. Any ideas?

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Not sure which board you are building, but I'd be looking closely at the 74C273 chip (part number may vary), but that would be one of the common points that would cause you problems for mulitple channels, consecutively. Make sure all 20 pins are soldered, etc.

And you're sure everything looks ok with the R16 network?

Might be worth putting that board under the magnifier one more time, checking for shorts, and reheating connections just to be sure.

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I solder boards under a microscope as part of my day job. There’s a lot of times that an IC pin will look fine with the naked eye (and I have very good eyes up close) but under the microscope, only the pin is soldered and it didn’t flow onto the pad.

It’s worth resoldering even the pins that look good. You won’t know which one was bad but who cares, you have a working board.

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  • 4 weeks later...

I just wanted to add a similar experience I had and what the problem turned out to be... ;)

I also had channels 5 thru 8 not working so I thought maybe I messed up the soldering or put the wrong resistor network in R16. I checked, resoldered, checked again, resoldered more, checked, swapped a couple resistor networks, and man I was stumped.

Then I got my DMM out and measured good voltage and the tabs on channels 5 thru 8? WTH???

Turns out the vampire ends I used were bad??? All four of them I couldn't get to work even when re-terminating them. I ended up putting four new ends on and I was good to go. Talk about going in circles???

So anybody reading this in the future... remember to check the simple things. :D

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