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jacob80

Megasquirt powers off after a few seconds

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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:

 

Screenshot2010-07-28at113518PM.png

 

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.)

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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..."

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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.

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