[SOLVED] energy meter problem

hi everyone,
i have a energy meter, it have a strange problem.
it show the correct frequency, but read the power and current as zero and voltage more higher of the real value (268v)


the follow picture show the frequency 49 hz


i opened the housing and i checked the components on the board but i have a doubt on one of this.

on board in its place printed zener diode simbol, but i don't know its feature.
it is an smd component.
on its body there is not any label, but only one blue line and the rest is orange colour


with my instrument (tester) it is in short circuit, so i think that first thing to do is to replacede it.
do you have some knowledge on this component.

i attach some picture of energy meter and the zener diode.
thank you so much everyone
erchiu

erchiu said:

hi everyone,
i have a energy meter, it have a strange problem.
it show the correct frequency, but read the power and current as zero and voltage more higher of the real value (268v)


the follow picture show the frequency 49 hz
..............
it is an smd component.
on its body there is not any label, but only one blue line and the rest is orange colour

Click to expand...

Have you connected a known load to the energy meter?
Then do the check .
How did the component is suspected as a faulty one?

of course,
i tryed different know loads, i read always zero amperes and zero watts.
only the frequency is correct. the voltage instead is more higher 268 v instead 220 v.
i removed the component (zener diode) because in short circuit (i measured on board).
after i measured it on my workbench and always in short circuit.
i guess is not should be in short circuit, rigth?

erchiu said:

of course,
i tryed different know loads, i read always zero amperes and zero watts.
only the frequency is correct. the voltage instead is more higher 268 v instead 220 v.
i removed the component (zener diode) because in short circuit (i measured on board).
after i measured it on my workbench and always in short circuit.
i guess is not should be in short circuit, rigth?

Click to expand...

without the circuit diagram , it will be a wild guess for the solution.

if zener short is confirmed , replacement and check is one option.

other than that , such meters may have a self test routine .
if you can activate it , then some clues may be available.

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srizbf said:

without the circuit diagram , it will be a wild guess for the solution.

if zener short is confirmed , replacement and check is one option.

other than that , such meters may have a self test routine .
if you can activate it , then some clues may be available.

Click to expand...

added:
self test option only if it has a controller.

your energy meter may or may not have one.

since it reads frequency and not power ,
my advice is to check the cureent sensing resistor that is usually included in the energy meter.

if you have exceeded the current rating at any time during the mesurement , then it would have gone.

(what is your meter rating ? voltage/current/frequency?)

the photos that are included didnt give clear idea .

may be a full view with high resolution and no flash reflection on the photos may do good.

still , as said , this is wild guess.


regarding zener , sometimes it may have been an inductor.(some energy meter circuits refer coils as Z).

unfortunately, i have only user manual of this meter, no service manual.
i measured all the components that i am able to measure and i found only zener failure.
under of this the simbol is of an zener as the picture.



the energy meter could be also other problems, but i wanted first of all and to see its behaviour.
there is not a way for identify this diode without component list?
thank you erchiu

One way you could try to find the voltage of the zener is to replace it with a variable resistor, starting off with the resistor at zero ohms. Be careful as the circuitry could all be connected to the mains. Connect a DC voltmeter across the VR and adjust the VR until the meter reads 1V. Check to see if the device is working (extremely unlikely). Readjust the VR to 2V drop, and check again. So if the zener is part of a DC voltage regulator, eventually the Vcc it supplies will be within the working range of the device and if that is the only fault , it should spring into life. I would not go beyond 12V. If you find that it works on say a 4V drop use a 5V zener as a replacement.
It could be that the zener is part of a voltage reference against which measurements are calibrated, so you might find that your voltage, which is reading too high at present falls to a more accurate level.
Frank

erchiu said:

unfortunately, i have only user manual of this meter, no service manual.
i measured all the components that i am able to measure and i found only zener failure.
under of this the simbol is of an zener as the picture.



the energy meter could be also other problems, but i wanted first of all and to see its behaviour.
there is not a way for identify this diode without component list?
thank you erchiu

Click to expand...

assuming that it is zener that has gone ,
can you trace the circuit around zener ,
and attach it.

a clear handdrawn circuit is enough.

will try.

i connected the energy meter on AC line without zener diode and it is working ok!
i connected at it an light led for to try.
starting to the top, the display show:
real time (hour:minute)
power (watt)
frequency (hertz)




pressing an button the display show:
-voltage (volt)
-current (ampere)
-total time (hour)


the circuit is power supply with 4,5 volts (3 batteries in series), but now i discovery that it work also without batteries when it is connected to AC line

these are others picture of the board and display.
there are two coupled boards both with the tracks on two sides.
i do them with higher resolution
this is show the simbol printed under the zener diode (d4)

the follow show the back side of that above:
here there is an little 78l05 (voltage regulator)
i checked also the big resistor (4,7 ohm colour yellow,green,gold,gold) and it's ok.

the next picture show the back side of display board

same picture with the plug for connection to main board.

one of three IC back the display board


the questions now are these:
i can to use this instrument in this way?
what good is this zener?
thank you so much everyone

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I'm sorry, but I had not seen your answers

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what range i must to use for variable resistor?
thank you

If the device can work of 4.5V then its processor is rated fro 3.3V Vcc and the zener probablely stabilises the Vcc at 3.3V. if you run it from the mains , your 3.3V line will be , say 3.9V or more leading to components over heating and being unreliable. Manufacturers do not normally wire in extra components without a good reason.
Frank

thank you chuckey,
i followed your suggestion.
i have connected an trimmer from 4,7 kohm instead the zener diode starting it to zero ohm.
so, i adjusted it and until 3,3 volt (about) the voltage shown was always high and the power shown was zero.
adjusting still, when the voltage on trimmer was about 5 volts the voltage shown from energy meter was same real value, but the power value was still zero.
about to 7,5 volt , the power shown also, was ok.
so i to tried with various zener diode values, starting from 3,3v_4,7v_5,1v_5,6v until 6,2v.
this last and 'was the right one.
now the energy meter working good.
thank you so much





current absorbed from led light


the new zener diode in its place


energy absorbed by my welder