# Can this multimeter be repaired?

Joined Nov 21, 2018
810
Hi,
I have a MasterCraft digital Multi meter, which can't measure the resistance now as picture show.
I just guess if it can be easily repaired?
All resistance arrange got random number in empty test prod.
Thanks

#### DickCappels

Joined Aug 21, 2008
8,685
And if you short the test probes together what do you get?

Do you know how an ohmmeter like this works?

You won't know whether it is easy to fix until you try. Most likely, if the meter has been treated nicely (nobody tried to measure the resistance of the AC mains, etc.) the problem is likely to turn out to be a poorly working switch contact, a broken component, or poor soldering.

#### Martin_R

Joined Aug 28, 2019
105
Noticed the 'bat' indicator is on. First thing to do is replace the battery.

#### rsjsouza

Joined Apr 21, 2014
350
From what it shows, @Martin_R may be right indeed. Ideally, low battery illumination should have a setpoint to just warn the user of an impending need for a battery change without influencing the measurements, but not all meters follow this rule.

If the battery change does not help, the multimeter's PCB may be dirty. I would open it and check for grime and/or residue around the input jacks and other components. Isopropyl Alcohol helps with this. Post good resolution pictures of both sides of the board so we can try to spot anything.

Obviously that, in the end, it may well be a bad switch or a broken component as @DickCappels mentioned.

Joined Nov 21, 2018
810
And if you short the test probes together what do you get?

Do you know how an ohmmeter like this works?

You won't know whether it is easy to fix until you try. Most likely, if the meter has been treated nicely (nobody tried to measure the resistance of the AC mains, etc.) the problem is likely to turn out to be a poorly working switch contact, a broken component, or poor soldering.
Thanks.
1. short the test probes together got 0 at R；
2. I don't know much about how an ohmmeter like this works? need help please;
3. The meter fall in this situation just after a mistake measure;

A picture attached, can you help by steps how to start?

Joined Nov 21, 2018
810
Noticed the 'bat' indicator is on. First thing to do is replace the battery.
Thanks.
I'll.

Joined Nov 21, 2018
810
From what it shows, @Martin_R may be right indeed. Ideally, low battery illumination should have a setpoint to just warn the user of an impending need for a battery change without influencing the measurements, but not all meters follow this rule.

If the battery change does not help, the multimeter's PCB may be dirty. I would open it and check for grime and/or residue around the input jacks and other components. Isopropyl Alcohol helps with this. Post good resolution pictures of both sides of the board so we can try to spot anything.

Obviously that, in the end, it may well be a bad switch or a broken component as @DickCappels mentioned.
Thanks.
The reason is a mistake measurement. Guess measured a high V in a wrong gear.

#### Deleted member 115935

Joined Dec 31, 1969
0
if your lucky ,
you've blown the fuse, I cant see from the photo,

if your unlucky, its the IC under that black blob if plastic,
impossible to repair,

Joined Nov 21, 2018
810
if your lucky ,
you've blown the fuse, I cant see from the photo,

if your unlucky, its the IC under that black blob if plastic,
impossible to repair,
Thanks.

Joined Nov 21, 2018
810

#### panic mode

Joined Oct 10, 2011
2,114
to be more sure you may remove PCB and check the other side. there may be more components or signs of trauma on the rotary switch...

#### DickCappels

Joined Aug 21, 2008
8,685
When the rotary switch has problems, that's a really bad sign.
Thanks.
1. short the test probes together got 0 at R；
2. I don't know much about how an ohmmeter like this works? need help please;
3. The meter fall in this situation just after a mistake measure;
(Some text removed for clarity)
1. A good sign. There is hope that this is still working.
After you replace the battery per @Martin_R measure some resistors and see whether it is working correctly or not.

2. I don't know much about how an ohmmeter like this works? need help please;

The measurement circuitry measures the voltage across the probes and applies a constant current to them. The IR drop shows up as voltage across the probes. There may be other means but this is the only means I have noticed on inexpensive meters and several expensive ones too. Knowing this might help you find the problem.

3. Please describe the mistake measure? That might help to figure this out.

Even if you can't get it working again the way you like it, all is not lost, now you have a set of resistors that you can use to make a precision voltage divider for your own projects if you decide to scrap the meter.

Joined Nov 21, 2018
810
Result report:
Take some time trying to do some thing.
Measured one of it's Transistor 1AM, measured all pins total 6 reads = 001, guess its gone, removed and measured again, not that bad, but the Soldering joints seems all three just conduct? anyway changed another one transistor of BC547. The R aranges 20K and 200K work, others still fault as was.

Joined Nov 21, 2018
810
Careful with the springs/contacts/bearings that may fly off.
Thanks.
I should have saw your post early.
That did.... and I replaced it.

Joined Nov 21, 2018
810
When the rotary switch has problems, that's a really bad sign.

1. A good sign. There is hope that this is still working.
After you replace the battery per @Martin_R measure some resistors and see whether it is working correctly or not.

2. I don't know much about how an ohmmeter like this works? need help please;

The measurement circuitry measures the voltage across the probes and applies a constant current to them. The IR drop shows up as voltage across the probes. There may be other means but this is the only means I have noticed on inexpensive meters and several expensive ones too. Knowing this might help you find the problem.

3. Please describe the mistake measure? That might help to figure this out.

Even if you can't get it working again the way you like it, all is not lost, now you have a set of resistors that you can use to make a precision voltage divider for your own projects if you decide to scrap the meter.
Thanks.
Actually I have a few of Multi meters, juts like to learn some thing from it.
1. changed a new battery, same;
2. learning.
3. All other measurement well, the R can't read, and got value when empty.

#### DickCappels

Joined Aug 21, 2008
8,685
It may be time to assign this one to the scrap heap. I have a Fluke DMM that is 32 years old. The resistance measurement stopped working about a year ago, but it is still very good for everything else. I think I value its accuracy, which has been verified over the years over the value of a few scrap parts.

The meters that cost $10 to$20 though, which are very good values, I can easily value for their parts over performance when things go south.

#### Audioguru again

Joined Oct 21, 2019
4,539
I am glad that I paid a little extra for my 32 years old Fluke DMM that still works perfectly today.

#### Audioguru again

Joined Oct 21, 2019
4,539
You should see the quality of the probes.
My 32 years old Fluke probes (they are marked "Fluke") are looking a little dirty but they work perfectly.