EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: ober on April 28, 2021, 04:37:57 pm
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I have a Metrahit 27M that has one component (literally) vaporized, including a PCB trace leading to it. Since the fuse was missing at the time I got it, I think I can imagine what happened. Now I would like to put back the missing component, in order to see how much of the rest of the multimeter still operates. But I can't find any hi-res photos of the PCB (or, heaven forbid, schematics). The component is close to what might be MOVs or PTCs, visible even without the inner cover removed.
Did existing owners of 27M (or 27I) multimeters take such PCB photos?
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Oh, here is a photo:
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It is probably something in parallel or in series with the input. If it is in parallel, just leave it like this. If in series, put a jumper. It is probably the best shot to quickly test the input and see if the meter is alive. If you get positive result, then it is worth to dig some more, and think what this part might be...
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In DCV mode, the display is fluctuating between a couple V and a couple hundred V. Putting in a voltage or shorting the leads doesn't change things, but coupling in a bit stray AC to one or two of the leads does (up to a beeping overload indication).
So it seems the gap is in series. Just right to it is a 0-ohms resistor (probably also as a fusible), so another one of those might be the most likely assumption.
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You're probably right.
Before going straight for a 0 Ohm you could try fitting 10k ohms as a current limiting test, it may give you 10k added offset on Ohmmeter and should have little noticeable effect on Voltmeter.