electro-music.com   Dedicated to experimental electro-acoustic
and electronic music
 
    Front Page  |  Articles  |  Radio
 |  Media  |  Forum  |  Wiki  |  Links  |  Store
Forum with support of Syndicator RSS
 FAQFAQ   CalendarCalendar   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   LinksLinks
 RegisterRegister   ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in  Chat RoomChat Room 
 Forum index » Wanted, For Sale, Opportunities and Requests » Parts and Components
Resistor: confusion
Post new topic   Reply to topic Moderators: Scott Stites, Uncle Krunkus
Page 1 of 1 [9 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Author Message
rogerlatur



Joined: Dec 22, 2012
Posts: 118
Location: france

PostPosted: Wed Aug 21, 2013 7:45 am    Post subject: Resistor: confusion Reply with quote  Mark this post and the followings unread

I have a populated PCB and I want to check resistors values.
With the colors I get completely different values than the one listed in the BOM of the project, a module I bought populated and which a couple of functions are faulty, so I decided to check the circuit.
My question: with a DVM, when the board is not powered on, do I get the exact value between the 2 legs of a resistor which is soldered or not?
Now I get other values and it confuses me even more, so I am not sure the resistor is not influenced by the circuit, even when powered off.
This is why I ask here before I turn mad.
Back to top
View user's profile Send private message
PHOBoS



Joined: Jan 14, 2010
Posts: 1754
Location: Moon Base
Audio files: 347

PostPosted: Wed Aug 21, 2013 9:26 am    Post subject: Reply with quote  Mark this post and the followings unread

it depends on the circuit. Sometimes it'll work, other times you'll measure a resistance that is lower (it should never be higher).
removing IC's can be helpful in some cases.

_________________
"My perf, it's full of holes!"
http://phobos.000space.com/ http://www.acidtrash.com/ Stickney Synthyards
Back to top
View user's profile Send private message Visit poster's website AIM Address Yahoo Messenger MSN Messenger
Blue Hell
Site Admin


Joined: Apr 03, 2004
Posts: 20589
Location: The Netherlands, Enschede
Audio files: 148
G2 patch files: 318

PostPosted: Wed Aug 21, 2013 9:58 am    Post subject: Reply with quote  Mark this post and the followings unread

PHOBoS wrote:
(it should never be higher).


Unless the board was powered not too long ago - some capacitors may still hold a charge then which is always good for some extra confusion.

edit:

What you can try is to swap your measuring leads, when it reads the same value then you can be more sure about the readout - however it can still be lower than expected even then (when there are parallel resistors on the board).

_________________
Jan
Back to top
View user's profile Send private message Visit poster's website
rogerlatur



Joined: Dec 22, 2012
Posts: 118
Location: france

PostPosted: Wed Aug 21, 2013 11:48 am    Post subject: Reply with quote  Mark this post and the followings unread

Thank you for helping me here !

Blue Hell wrote:
however it can still be lower than expected even then (when there are parallel resistors on the board).

This is what made me wondered.

I know there is another solution, while powering the module on and measuring current + voltage, will give me the resistance. But I think I will post some pictures and ask here what you think, so that I am able to check all values relative to color codes after I got your advices.
Back to top
View user's profile Send private message
rogerlatur



Joined: Dec 22, 2012
Posts: 118
Location: france

PostPosted: Thu Aug 22, 2013 5:34 am    Post subject: Reply with quote  Mark this post and the followings unread

...
Last edited by rogerlatur on Fri Aug 23, 2013 2:20 am; edited 2 times in total
Back to top
View user's profile Send private message
rogerlatur



Joined: Dec 22, 2012
Posts: 118
Location: france

PostPosted: Thu Aug 22, 2013 5:56 am    Post subject: Reply with quote  Mark this post and the followings unread

...
Last edited by rogerlatur on Fri Aug 23, 2013 2:21 am; edited 1 time in total
Back to top
View user's profile Send private message
rogerlatur



Joined: Dec 22, 2012
Posts: 118
Location: france

PostPosted: Thu Aug 22, 2013 6:52 am    Post subject: Reply with quote  Mark this post and the followings unread

I unsoldered the
White Brown Orange Brown (Red)
because I want 91K not 9.1K
I wanted to put it with my 9.1K stock and replace it on the board with a 91K resistor, but first I measured it to control with my DVM. It shows 91.3K, not 9.13K !!!

I checked again in the online calculator and came to 9.13K.
I checked again the color code (on this old resistor the color is readable) and came to 9.13K.

If I take a 91K from my stock and measure it it says 90.8K (OK). It is:
White Brown Black Red (Red)

Why when I take this old unsoldered resistor
White Brown Orange Brown (Red)
and measure it it says 91.3K

It is weird!

The color code reading is very simple when colors are still readable, the measurement also with the DVM, mostly doing comparaisons to be sure (we never know !). I assume that some resistors can have wrong color codes then and this was really confusing.
Back to top
View user's profile Send private message
rogerlatur



Joined: Dec 22, 2012
Posts: 118
Location: france

PostPosted: Sat Oct 05, 2013 1:14 am    Post subject: Reply with quote  Mark this post and the followings unread

Update about these DIY modules that I bought "all done / complete" many years ago and never worked fine:
I simply changed all "weird" resistors. Most were completely wrong values and 2 had wrong color code indication compared to the measurements (or were faulty ?).
Anyway, the modules work now best with new resistors and the right values !
What a difference !
Back to top
View user's profile Send private message
Gaetano_AU



Joined: Oct 08, 2011
Posts: 49
Location: Australia

PostPosted: Sun Oct 06, 2013 7:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

Just for reference for anyone trying to check a resistor. The best way to check its value, is to unsolder one end and lift the end up out of the PCB, it's the only way to be sure what value it is.
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic Moderators: Scott Stites, Uncle Krunkus
Page 1 of 1 [9 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
 Forum index » Wanted, For Sale, Opportunities and Requests » Parts and Components
Jump to:  

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
e-m mkii

Please support our site. If you click through and buy from
our affiliate partners, we earn a small commission.


Forum with support of Syndicator RSS
Powered by phpBB © 2001, 2005 phpBB Group
Copyright © 2003 through 2009 by electro-music.com - Conditions Of Use