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EEVblog 121GW Multimeter Issues

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J-R:
Yes, I can see the plastic pulled away from the metal shield...

EEVblog:

--- Quote from: J-R on May 24, 2021, 02:47:16 am ---Looks like PTC3 was pulled away from PTC4.  On mine they are still stuck together, which keeps PTC3 out of the way. So it seems plausible the metal shield had been doing some cutting into PTC3.

--- End quote ---

Yes, but even if it "cut" into the heatshrink of the PTC you still have the device encapsulent, so that's not enough for a 240V on it's own to cause an issue.

J-R:

--- Quote from: EEVblog on May 24, 2021, 03:08:51 am ---
--- Quote from: J-R on May 24, 2021, 02:47:16 am ---Looks like PTC3 was pulled away from PTC4.  On mine they are still stuck together, which keeps PTC3 out of the way. So it seems plausible the metal shield had been doing some cutting into PTC3.

--- End quote ---

Yes, but even if it "cut" into the heatshrink of the PTC you still have the device encapsulent, so that's not enough for a 240V on it's own to cause an issue.

--- End quote ---

Dunno, that metal seems pretty sharp to me...  How much would it need to cut into the PTC before it causes a short?

Could it be a combination of the proximity of the metal and a catastrophic failure of the PTC?

Monkeh:
If the edge of that shield is sharp enough to cut through a PTC it shouldn't be allowed to flap in the breeze.

EEVblog:

--- Quote from: J-R on May 24, 2021, 03:15:03 am ---Dunno, that metal seems pretty sharp to me...  How much would it need to cut into the PTC before it causes a short?

--- End quote ---

Just tried to get my exacto knife into one and didn't get very far.


--- Quote ---Could it be a combination of the proximity of the metal and a catastrophic failure of the PTC?
--- End quote ---

Possible. Although the OP said it happened imediately when touching the mains, so that seems to rule out a surge as a contributing factor.
Maybe a combination of variability in the PTC encapsulent thickness on the top and a small cut into it?

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