Multimeter measuring resistors wrong

Thread Starter

vojt444

Joined Nov 25, 2022
9
Hello,
I have multimeter OWON B35T for about 4 years. My problem with this multimeter is when I want to measure resistors it doesn't measure values correctly. For example when I measure 120 Ohm resistor it shows value 12 Ohms etc... Even if I dont connect any resistor to measure the multimeter shows value around 118 Ohms.
Is any possibility to repair that or can I throw in the trash can and buy a new one?
Can someone explain how this can happen? Can the multimeter somehow break itself like this or did I somehow cause it?
Thank you
 

Ya’akov

Joined Jan 27, 2019
6,856
Welcome to AAC.

Do other ranges work properly?
Are the batteries good?
Did you accidentally measure a high voltage while in resistance range?
 

Thread Starter

vojt444

Joined Nov 25, 2022
9
Welcome to AAC.

Do other ranges work properly?
Are the batteries good?
Did you accidentally measure a high voltage while in resistance range?
Yes, other ranges seem to work fine.
Batteries are fine.
I maybe measured resistor when the circuit was active, but there was max 5 V.
 

Ya’akov

Joined Jan 27, 2019
6,856
Can you take some photos of the meter malfunctioning showing where the leads are plugged in, with the range switch is set to, and what the display says? It’ll make it a lot easier to help you if we can see what you see.
 

MisterBill2

Joined Jan 23, 2018
13,805
I once repaired a multimeter for a friend, which had a similar problem. No fault was obvious except for a slightly sticky film everywhere.
What had happened is that a previous battery for the resistance function had deposited a conductive mist over everything. So I removed the new batteries and very carefully washed all of the wiring and switches with a lot of hot water. I was careful to avoid getting water into the meter movement section. I washed it for quite a while, about ten minutes. Then I dried it and rinsed it with alcohol after it had dried for a couple of hours. Then I let it bake in a hot car for a day. After that I put the battery in and it worked very well.
So the lesson learned is never leave carbon-zinc batteries in a piece of equipment.
If the other ranges really do read correctly, then there may be just a bit of contamination around the switch, or around the battery area.
 

Thread Starter

vojt444

Joined Nov 25, 2022
9
Can you take some photos of the meter malfunctioning showing where the leads are plugged in, with the range switch is set to, and what the display says? It’ll make it a lot easier to help you if we can see what you see.
Of course, there is one photo with 10k resistor and one without a resistor
IMG_20221205_202325.jpgIMG_20221205_202308.jpg
 

MisterBill2

Joined Jan 23, 2018
13,805
I see a "range" button and think that the meter may not be quite auto ranging. In fact, it may have a few functions that are strange to control. That would probably lead to strange readings. So a study of the instruction book may be in order.
 

Dodgydave

Joined Jun 22, 2012
10,591
The range button is for manual mode, each press of the button increases the range from the lowest to highest, it seems strange that with nothing connected to the probes it should read OL..

Screenshot_2022-12-06-13-45-30-501_com.adobe.reader.jpg
 

MisterBill2

Joined Jan 23, 2018
13,805
I am wondering if this error response is related to the range selection and the range in use. It seems that probably the resistance measurement is done by passing a specific current through the resistor and measuring the voltage developed.
One accidental application of voltage may have damaged a current regulator circuit, as not all meters are adequately protected against errors in use. Not sure how to verify that without additional test equipment.
 

Tonyr1084

Joined Sep 24, 2015
7,199
I maybe measured resistor when the circuit was active
When measuring resistors in circuit - other parts of the circuit will skew the reading. If you have two 100Ω resistors in parallel your meter will read 50Ω. Other variations will produce different results.

Was going to comment about shorting your leads together. Though someone else mentioned it - I'd suggest shorting them together then pressing the blue delta button. Then test your free hand resistors again. It's purpose is to negate any potential variations in the test leads.
1670339177596.png
Now that I mentioned test leads - there's a possibility you may have a faulty connection in the socket or the leads themselves may be interfering with the reading. Short them together and test for zero ohms. While testing, move the leads about. Flex the leads where they enter the meter and at the test probes. Also wiggle the leads at their sockets. They can be dirty - or I once had a meter with fractured solder where the test leads were connected to the board inside the meter.
 
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