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4hv.org :: Forums :: General Science and Electronics
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DMM repair

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...
Tue Aug 01 2006, 02:57AM Print
... Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
Ok, I accidentally gave my protek 506 a bit more juice that I was supposed to (well I thought it was a low voltage transformer...) dead and it arked over in the traces for the mode selector dial... But that wasn't much of a problem (just scrape off the carbon and all is good)

BUT there were 2 components in series with the input labled ptc1 and 2 that look like thermistors, ao I am guessing that they were ptc thermistors. The the only problem is that I don't know what type... I measured the one that was not burnt and it read about 500ohms, but if I replace the other one with a 500ohm resistor the resistance calibration is off (it reads like 75ohms at a dead short). If I short either of the 2 thermistors it reads correctly...

Does anyone have one laying arround that you could measure for me to see what they should be? For now they are shorted, but I would like to put them back in wink
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Wolfram
Tue Aug 01 2006, 01:29PM
Wolfram Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
PTC1 = 350.8 ohms and PTC2 = 355.6 ohms when measured in-circuit. The temperature here is around normal room temperature. However, my Protek is broken in some way too, because a dead short measures as 256 ohms in resistance mode, so I wouldn't trust these numbers blindly.
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...
Tue Aug 01 2006, 03:15PM
... Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
hmm, perhapse a bulk buy once we get the right number tongue
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Conundrum
Thu Aug 03 2006, 06:26PM
Conundrum Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059
lol.. sounds like my meter. i think ptcs are a type of overvoltage crowbar.

-A
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