Bad resistors
in [Design]
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From: crasic on 23 Jun 2010 03:49 On Jun 22, 10:00 pm, "Phil Allison" <phi...(a)tpg.com.au> wrote: > "Jan Panteltje" > > > Got 10 resistors on tape marked 2M7. > > Used one, circuit did not work right. > > Took some testing ... before I measured the resistors. > > Of the 10 several are 620 k and not 2M7. > > Bought fromwww.voti.nl, so beware. > > All are marked with the right color code for 2M7. > > > New to me :-) > > ** Though pretty rare, I have come across wrongly marked resistors in a > piece of commercial equipment !! > > Dozens of resistors colour coded as 3.3kohms were in fact 4.7 kohms. > > The correct value WAS 4.7 kohms - so the equipment maker knew about the > wrong coding !! > > .... Phil The bands can change color, especially with age or heat. Or it could have been a batch of mismarked resistors that the equipment maker got for cheap
From: JW on 23 Jun 2010 05:21 On Tue, 22 Jun 2010 22:59:38 GMT Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote in Message id: <hvrf99$5u8$1(a)news.albasani.net>: >On a sunny day (Tue, 22 Jun 2010 22:09:48 GMT) it happened nico(a)puntnl.niks >(Nico Coesel) wrote in <4c21346d.364231437(a)news.planet.nl>: > >>Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: >> >>>Got 10 resistors on tape marked 2M7. >>>Used one, circuit did not work right. >>>Took some testing ... before I measured the resistors. >>>Of the 10 several are 620 k and not 2M7. >>>Bought from www.voti.nl, so beware. >>>All are marked with the right color code for 2M7. >> >>Sure you didn't hold the resistors while measuring? > >LOL, no I know about that one :-) >I was so suprized I measured them 3 times, and then again a little later. I have a pair of Fluke test leads that when measuring high resistance I'll get a low reading if the leads are touching each other, though nowhere near what you're seeing, perhaps about 5% error. I'd also check your resistors on another meter for verification.
From: Sylvia Else on 23 Jun 2010 05:28 On 23/06/2010 9:54 AM, DrParnassus wrote: > On Tue, 22 Jun 2010 21:51:47 GMT, Jan Panteltje > <pNaonStpealmtje(a)yahoo.com> wrote: > >> Got 10 resistors on tape marked 2M7. >> Used one, circuit did not work right. >> Took some testing ... before I measured the resistors. >> Of the 10 several are 620 k and not 2M7. >> Bought from www.voti.nl, so beware. >> All are marked with the right color code for 2M7. >> >> New to me :-) > > A normal handheld DVM barely measures 1MOhm correctly so anything up > there and over will not likely be easily measured with cheap handhelds. Still, you'd expect it to give the same wrong reading for the same resistances. Sylvia.
From: Sylvia Else on 23 Jun 2010 05:30 On 23/06/2010 3:00 PM, Phil Allison wrote: > "Jan Panteltje" >> Got 10 resistors on tape marked 2M7. >> Used one, circuit did not work right. >> Took some testing ... before I measured the resistors. >> Of the 10 several are 620 k and not 2M7. >> Bought from www.voti.nl, so beware. >> All are marked with the right color code for 2M7. >> >> New to me :-) > > > ** Though pretty rare, I have come across wrongly marked resistors in a > piece of commercial equipment !! > > Dozens of resistors colour coded as 3.3kohms were in fact 4.7 kohms. > > The correct value WAS 4.7 kohms - so the equipment maker knew about the > wrong coding !! Or just fed strips out of the 4.7K box into the machine that loads components onto the board, and never noticed that they were marked as 3.3K. Sylvia.
From: Jan Panteltje on 23 Jun 2010 06:16
On a sunny day (Tue, 22 Jun 2010 16:54:15 -0700) it happened DrParnassus <DrParnassus(a)hereforlongtime.org> wrote in <56j226hlh3iloar347o4bgsc3qjt0s61ks(a)4ax.com>: >On Tue, 22 Jun 2010 21:51:47 GMT, Jan Panteltje ><pNaonStpealmtje(a)yahoo.com> wrote: > >>Got 10 resistors on tape marked 2M7. >>Used one, circuit did not work right. >>Took some testing ... before I measured the resistors. >>Of the 10 several are 620 k and not 2M7. >>Bought from www.voti.nl, so beware. >>All are marked with the right color code for 2M7. >> >>New to me :-) > > A normal handheld DVM barely measures 1MOhm correctly so anything up >there and over will not likely be easily measured with cheap handhelds. In fact this is a common mistake in thinking Say if your meter has a max of 2 MOhm, and you want to measure 2M7 resistors, then how to do that? It is easy, you put 2 in parallel, and that should read 1M35. I have often argued against buying YAOEPOE (Yet An Other Expensive Piece Of Equipment), as we have (well OK not everybody equal amounts) brains to tackle simple problems. hehe |