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Old 03-26-2008, 12:51 AM   #1
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Default Building MS- Q14 and Q15?

I'm building the MS and want to make sure I'm not crazy here. I have just installed Q14 and Q15, which is right after installing R37 and R38 for the driver FET current limiting circuit. Whenever I have soldered closely spaced parts like these transistor legs, I've checked continuity with my meter to make sure I haven't bridged any connections, and I haven't messed up any yet but these have me wondering.

I'm showing continuity between two of the three legs, on both Q14 and Q15, and they sure don't appear to be bridged by mere visual inspection. The thing is, it might be because the only thing between those two legs (verified with the schematic) is R37 or R38, which are only 0.5 ohms. My meter reads continuity across R37 or R38 alone, and I believe lacks the precision to consistently measure anything below 1 ohm and just sounds the continuity beep.

I wouldn't wonder at all if I hadn't just replaced the soldering iron tip, and I had to hold it on the components a bit longer to get the solder to flow. If you get the transistor too hot, can it be internally shorted? If that happened, would there even be any significant consequences given that it's only bypassing a 0.5-ohm resistor in a circuit that is supposedly optional to install? Or should I quit worrying and assume everything's fine until the magic smoke leaks out?

EDIT: Well spank my *** and call me Charlie, a more thorough search reveals that I'm not the only one who had this problem.
Guess I was worrying over nothing.

Last edited by ScottFW; 03-26-2008 at 01:07 AM.
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Old 03-26-2008, 01:05 AM   #2
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You can kill a transistor with too much heat IIRC from tech class in 6th grade.

2 legs of Q15 were jumped for me on a premade MS. It didn't cause any permanent damage. It only caused injectors 1 and 3 not to fire. That took me 2 weeks to figure out.
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Old 03-26-2008, 01:11 AM   #3
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I was editing while you were replying. I think I'll assume it's okay and was just the low resistance reading as continuity. But I will put it in my little miscellaneous notes file as a possible culprit in case I have injector problems when it's installed.
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Old 03-26-2008, 01:20 AM   #4
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I wouldn't worry to much about it. Normally you shouldn't have continuity but I have seen some weird results from testing installed transistors like that.

Sand the tip of your iron, then re-tin it and keep it clean this time.
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