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Thread: Quick question for engineers

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    Quick question for engineers

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    So I'm working on this mod, and I like to check continuity along the way (instead of all at once at the end) because there's a lot of steps. I don't know a ton about electronics (as this thread will make clear), but I know enough to (usually) successfully complete some little projects like this.

    The issue is, on this one resistor, I'm not getting continuity on one side of it.

    On the attached schematic, it's R7 (150 ohm). I'm getting continuity on the one leg that's going to R34, but on the end that's going to the transistors (Q10 and Q11), I'm not.

    It wasn't until I took this picture that I noticed what appears to be a severed trace. I had looked under a magnifying glass at it, but I guess the light wasn't right or something. This morning when I took the picture (for this post), I noticed it (see photo).

    If it is indeed a lifted trace, I have no problem making a jumper. Before I do that, though, I just wanted to double check that there's nothing special about checking continuity with transistors. In other words, I should be able to get continuity from the point A (top leg of R7) to point B (transistor), even without current running through the circuit, correct?

    I know this is probably a really stupid question, but before I noticed that issue with the lifted trace in the photo, I couldn't tell if that actually was a trace or if it was just maybe a scratch. In the photo, it's much clearer that it almost certainly is a trace that's been severed.

    Thanks!
    Attached Thumbnails Attached Thumbnails mod-schematic-jpg   pcb-jpg  
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    Hi,
    It does look pretty clear cut.
    I think you've figured it out for yourself.

    Point B on your diagram looks like the pair of transistor legs that should connect to top of r7 in your schematic, and it looks like the trace there has been damaged and curled back towards point B.
    The easiest thing to do is to replace R7 but leave the leg long and bent it back towards B, solder it on, and snip the excess off at that point,
    or just solder in a little piece of bridging wire/component leg.
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    Quote Originally Posted by Steenamaroo View Post
    Hi,
    It does look pretty clear cut.
    I think you've figured it out for yourself.

    Point B on your diagram looks like the pair of transistor legs that should connect to top of r7 in your schematic, and it looks like the trace there has been damaged and curled back towards point B.
    The easiest thing to do is to replace R7 but leave the leg long and bent it back towards B, solder it on, and snip the excess off at that point,
    or just solder in a little piece of bridging wire/component leg.
    +1. WRT to continuity checks around transistors? Yes, should be fine and most DDMMs I have used do not produce enough voltage to turn on Silicon devices (but might Germanium). You can check though, if you get a reading that does not tally with the schematic, reverse the leads and see what you get then.

    'Diode Mode' will of course cause devices to conduct.

    NB. Most meters have a 'Bleep' function. That MIGHT bugger some devices but is invaluable for checking cables on the fly.

    Tip from an old valve jockey: Sharpen the probes to a needle point so they stab through PCB resist.

    Dave.

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