jacob80 Posted July 29, 2010 Share Posted July 29, 2010 Hey guys! Well I've run into a problem I can't seem to pinpoint myself. Lately, I've been working on installing an additional relay output on my PCB in which I have successfully done just that, but not I've run into another issue. Last night, I was performing some tests on my new output when, after about 5-10 seconds (it will vary some), all lights went out and all Megatune gauges went red and there was no signal from the computer. Upon removing the stimulator board and reinstalling it, it would sometimes come back on but it would not come back on if you left it plugged into the board for an extended time and tried this. When the stim was plugged in, I could adjust all the knobs and everything worked fine. My stimulator is powered by a plug-in wall adapter and I confirmed it was getting power and it is (~12.5v DC). After I confirmed this, I went ahead and performed this test with the exception of one of the steps: "stim voltage (~9 Volts), on the pin nearest the DB9, the middle one should have less than 1 Ohm to ground (use the heat sink, or the center pin of the voltage regulator, as a ground), and 5.0 Volts on the pin furthest from the DB9." The step I did not fully complete is the resistance test. IIRC, I put the black lead of my multimeter on the "GND" of the proto area and the other on the middle pin of U5 and had a reading of ~1.7ohms IIRC and it says the resistance should be less than 1.0ohms, so perhaps this is my problem and I just need a new voltage regulator at U5. Here is a datalog right before the Megasquirt powers off. I'm looking at the voltage and I want to believe that is my problem: Thanks for your help guys, I do appreciate it! (Matt Cramer, I have emailed you about this issue. This has been posted on the Megasquirt forums, as well.) Quote Link to comment Share on other sites More sharing options...
jacob80 Posted July 30, 2010 Author Share Posted July 30, 2010 Stimulator Board power voltage: 13.79v S12: 13.86v S12C: 12.86v Center leg of Q9: 13.79v Center leg of Q12: 13.79v Non-banded end of D3: 13.75v Left leg of U5 (closest to DB9): 12.8v Banded end of D9: 12.75v And for the 5v stuff: S5: 4.046v Two +5V holes in the proto area: 4.037v Non-banded end of D9: 4.987v Right leg of U5: 4.990v Banded end of D19: 4.041v CPU Pin 1: 4.035v CPU Pin 20: 4.035v CPU Pin 31: 4.048v Everything looks to be up to spec! However, when placing the negative leads of my multimeter on the Gnd of the proto area and the positive lead of the multimeter on the center pin of U5, I get a resistance of -2.0ohms (the multimeter leads have .2ohms of resistance). Is this okay? I'm concerned about this because of what I read in the megamanual: "the middle one (pin of U5) should have less than 1 Ohm to ground (use the heat sink, or the center pin of the voltage regulator, as a ground), and..." Quote Link to comment Share on other sites More sharing options...
naviathan Posted July 30, 2010 Share Posted July 30, 2010 When it does power on, does the 5V regulator get hot really quick? Quote Link to comment Share on other sites More sharing options...
jacob80 Posted July 30, 2010 Author Share Posted July 30, 2010 It gets hot fairly quickly, but not super hot. I've ordered another one just in case. Quote Link to comment Share on other sites More sharing options...
naviathan Posted July 30, 2010 Share Posted July 30, 2010 Yeah I'd say that's probably it then. The 5v regulator shouldn't get warm until it's under a decent load, which the stim board doesn't provide, at least mine never has. Quote Link to comment Share on other sites More sharing options...
jacob80 Posted July 30, 2010 Author Share Posted July 30, 2010 I don't understand. How could it be faulty if it is receiving good input voltage and outputting the correct voltage? The only potential issue I could forsee is the ground resistance. Please enlighten me, I am interested! Quote Link to comment Share on other sites More sharing options...
naviathan Posted July 30, 2010 Share Posted July 30, 2010 It could be anything inside the chip causing it to heat up excessively and shutdown. If you think the ground resistance is the problem get the schematics and follow that trace to see what could be causing it. Could be a diode causing the resistance that needs to be changed, but I don't believe a high resistance on the ground pin would cause the 5v to over heat. Quote Link to comment Share on other sites More sharing options...
jacob80 Posted July 30, 2010 Author Share Posted July 30, 2010 Okay, I will try this. Matt Cramer suggested that because D21 and D19 are getting hot (which he said should be cold to the touch) I should replace these. I will let you know what I find out, the parts are on the way. Thanks man! Quote Link to comment Share on other sites More sharing options...
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