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Digital Multimiter issue

belkzak

Member
Hi guys,

I have a digital multimeter from TTI reference 1604, it was involved in a short circuit with no fuse installed, and now, it's not functioning.
When I connect it to the power, it makes some noise from its buzzer, and each time I touch its power plug, it displays something new on the screen as you see in the following pictures:

IMG20210613081114.jpg
IMG20210613081203.jpg
IMG20210613081147.jpg

Where do you guys think is the problem!
Thanks
 

Visitor

Well-Known Member
Can you explain what actually happened when the meter was "involved in a short circuit with no fuses installed"? It sounds like maybe you tried to measure current directly from terminals on a power supply or wall socket?
 

belkzak

Member
Can you explain what actually happened when the meter was "involved in a short circuit with no fuses installed"? It sounds like maybe you tried to measure current directly from terminals on a power supply or wall socket?
It's not the case actually, it was installed in the setup that you can see in the following picture:

1623757202438.png
and the triac pins where shorted unintendedy, furthermore, the potentiometer blew up.
 

MacIntoshCZ

Active Member
It's not the case actually, it was installed in the setup that you can see in the following picture:

View attachment 131923
and the triac pins where shorted unintendedy, furthermore, the potentiometer blew up.
I dont know what you are talking about. You realized this schematic and connect ammeters (one 10A rating and second 10mA) from multimeter at the same time??? If you did so, congrats. Its kinda stupid, you connected 230V through 1k resistor and potentiometer to pwm.
 

belkzak

Member
I dont know what you are talking about. You realized this schematic and connect ammeters (one 10A rating and second 10mA) from multimeter at the same time??? If you did so, congrats. Its kinda stupid, you connected 230V through 1k resistor and potentiometer to pwm.
I have connected two ampermeters ! the one in series with the triac gate is the one dammaged !
 

MacIntoshCZ

Active Member
I dont know what you are talking about. You realized this schematic and connect ammeters (one 10A rating and second 10mA) from multimeter at the same time??? If you did so, congrats. Its kinda stupid, you connected 230V through 1k resistor and potentiometer to pwm.
So i guess triac can not withstand 230V breakdown and then blown ammeter. 10mA rating one? Also check if yours multimeter ground is same as mains neutral. It needs to be isolated
 

belkzak

Member
So i guess triac can not withstand 230V breakdown and then blown ammeter. 10mA rating one? Also check if yours multimeter ground is same as mains neutral. It needs to be isolated
The question now iw how to repair the multimeter because it's blocked !
 

MacIntoshCZ

Active Member
The question now iw how to repair the multimeter because it's blocked !
Diagnose it and fix it? What do you expect?Search for blown things? No one is able to diagnose it remotely.
 
Last edited:

Visitor

Well-Known Member
If the pot blew up, the current through it and the meter was way more than 10mA. The meter should have fuses for current measurements.

You say there was no fuse – if the meter's fuses had been replaced with the wrong type of fuses, the meter would have no protection against too much current.

Based on what the meter is doing, its controller has been fried. It's beyond being fixed. Sorry to be the bearer of bad news.

If certain ranges didn't work, there might have been some hope of getting it to work. But in this case, there's little chance it can be fixed.
 

schmitt trigger

Well-Known Member
VLSI digital ICs don’t require to blow up to become damaged.
By the description of your problem, most likely the main processor is damaged, although I suspect that additional devices must be also defective.
At the bare minimum you require a service manual with a full schematic.
Vendor can provide them, for a fee.
Second, what sort of troubleshooting equipment do you have?
As Visitor mentioned, this will be very difficult to repair/ calibrate.
 

MacIntoshCZ

Active Member
VLSI digital ICs don’t require to blow up to become damaged.
By the description of your problem, most likely the main processor is damaged, although I suspect that additional devices must be also defective.
At the bare minimum you require a service manual with a full schematic.
Vendor can provide them, for a fee.
Second, what sort of troubleshooting equipment do you have?
As Visitor mentioned, this will be very difficult to repair/ calibrate.
It looks like its in school laboratory. If is so, yours teacher is not able to give you an advice?
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
More than likely, there are some unintentional grounds and/or you exceeded the negative lead to ground voltage. With a lot of Keithley instruments that I used, that max voltage was 30 V.

Unfortunately, I've never had to troubleshoot such a failure.

It's a silly circuit anyway. Square wave current measurement?
Seems like it measuring would be more suited for differential scope measuremnts or if this was a lab, reduce the voltage to something safe, like 24VAC maximum. e.g. use a energy limited 40VA transformer. You can short the output and nothing bad happens,
They are common in HVAC systems.
 

belkzak

Member
If the pot blew up, the current through it and the meter was way more than 10mA. The meter should have fuses for current measurements.

You say there was no fuse – if the meter's fuses had been replaced with the wrong type of fuses, the meter would have no protection against too much current.

Based on what the meter is doing, its controller has been fried. It's beyond being fixed. Sorry to be the bearer of bad news.

If certain ranges didn't work, there might have been some hope of getting it to work. But in this case, there's little chance it can be fixed.
Why do they have ADC inside then ? Signal is not passed to the microcontroller directly i guess
 

MacIntoshCZ

Active Member
I mean what can cause this kind of blockage ? nothing is appearing to be blown !
Sensor circuitry is probably gone. You can sell it on ebay as slightly used =).
hehe
 

MacIntoshCZ

Active Member
If the sensor circuitry is gone, why the display is blocked ? why the buzzer is always ON? my guess is the microcontroller !
And mcu cannot be part of sensor circuitry? :)
 

Visitor

Well-Known Member
If the sensor circuitry is gone, why the display is blocked ? why the buzzer is always ON? my guess is the microcontroller !
That's not a guess. It's virtually certain to be the case.

In the words of Star Trek's Dr. McCoy, "It's dead Jim."
 

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