jaytee Posted October 3, 2013 Report Share Posted October 3, 2013 I was just finishing up step 4 in the sammichSID assembly instructions and I'm running into a problem I want to fix before I get any further. On step 4.19, I am to check for shorts between all the voltage regulator pads. Everything seems to check out except the middle pin of my 7809 (should be ground) and the pin closest to the edge of the PCB. For some reason this connection is giving intermittent beeps when I test for continuity with my multimeter. I can't seem to reproduce it consistently, and 95% of the time it's fine, but that little beep every once in awhile has me worried enough to pause. My soldering skills are beginner, but there's no visible mistake I can see. No obvious shorts, the joints look OK.... Could I have fried a component somehow?....would that even cause a short? Checking some surrounding joints, I'm actually getting the same issue with the next nearest joint as well, one of the leads of C9. Ivette Reid redoing each of these joints with no change.... I'm afraid of doing more harm than good at this point; frying something trying to fix a joint that might not even be bad. Any ideas? Quote Link to comment Share on other sites More sharing options...
MrAureliusR Posted October 4, 2013 Report Share Posted October 4, 2013 (edited) Instead of measuring continuity, measure resistance. The threshold of multimeters for what is 'connected' can differ. It might be right on the edge of your meter's threshold so you get an intermittent beep, but its probably actually fine. Especially if you're confident in your soldering. Measure the resistance and post the values here. Plus what are these particular pins for? Obv the one on the regulator is ground but what's the other one? If its a voltage rail that has a capacitor going to ground nearby sometimes the ESR is low enough to trigger continuity (happened to me once a while back) and makes you think there's a problem when there isn't. (Or sometimes there is a problem like a bad cap or a short to ground) Edited October 4, 2013 by MrAureliusR Quote Link to comment Share on other sites More sharing options...
jaytee Posted October 4, 2013 Author Report Share Posted October 4, 2013 (edited) The resistance seems to be continuously increasing. I took a look at the circuit diagram and it looks like the non-ground pin on the voltage regulator is connected to a big capacitor. If I understand you correctly, that means the continuity and resistance readings I'm getting are correct, right? I'm not 100% confident in my soldering skills, but I'm even less confident in my electronics knowledge. I spent some time soldering a few years back, but it was all circuit-bending, so troubleshooting wasn't really part of the M.O. I just want to make sure everything's ok before I move further on this project. :) Edited October 4, 2013 by jaytee Quote Link to comment Share on other sites More sharing options...
MrAureliusR Posted October 4, 2013 Report Share Posted October 4, 2013 Can you post some numbers of what you're seeing? Quote Link to comment Share on other sites More sharing options...
jaytee Posted October 4, 2013 Author Report Share Posted October 4, 2013 I'll post some of the actual values when I get home after work today, but they never settled enough to get a single reading. Basically, the resistance value would start out negative, rise toward zero steadily, and continue well into the positive numbers until it passed the maximum number for whatever mode the multimeter was in. I do remember that the 200ohm mode (smallest possible setting on my meter) was too small to be much use; it'd pass zero and go past 200ohns within a couple seconds. With the multimeter in continuity mode, it would beep through all the negatives, right up to just past zero, then stop. I believe this is the expected behavior, yes? Like I said, I'll post actual values when I get home. I also took some pictures of the circuit boards and the areas in question, but they don't want to upload from my phone, so I'll have to post those when I get home as well. Quote Link to comment Share on other sites More sharing options...
kpete Posted October 4, 2013 Report Share Posted October 4, 2013 The readings that I observe you seeing are normal. If there is a short then you would be reading valves like .5 ohms or lower.When you measure across the capacitor of the power supply, your meter will measure it as an electrical short for a very short time. As the voltage being supplied by the meter charges the capacitor in the circuit, the ohms reading on the meter will increase until the capacitor is charged and no more current flows thru that capacitor.Before I apply power to any of my projects, I check for shorts with the ohm meter like you are doing, then I visually check that I haven't soldered the electrolytic capacitors in backwards. It never hurts to double check this.Pete Quote Link to comment Share on other sites More sharing options...
jaytee Posted October 4, 2013 Author Report Share Posted October 4, 2013 Awesome! I was really concerned at first, but the more I read and the more I learned here, the more things sounded normal. I'll get started on step 5 tonight, just as soon as I finish a visual inspection of the board like you said. Quote Link to comment Share on other sites More sharing options...
jaytee Posted October 10, 2013 Author Report Share Posted October 10, 2013 Just thought I'd update this thread in case anyone else has these readings and is confused about them. Continued the build without issue, everything worked out fine! Quote Link to comment Share on other sites More sharing options...
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