EMA-1 disassembly/technical - two battery version

There are two common versions of the EMA-1. There are major internal differences between the two versions. The version examined on this page uses two button cell batteries. The three battery version is examined here.

There is no point taking the device apart. There are no user serviceable parts inside. You do not need to take the device apart to replace the batteries. See the battery replacement section on the updated instructions page. If you do not like to take things apart for no reason, please skip this page.

Case front with display, controls, appliance socket

Buttons are: MASTER CLEAR (in recess), UP, SET, FUNC

ELTO EMA1 Power usage meter New Zealand lcd panel and buttons

Back panel

Text on back panel:

 Type  EMA-1 CS 07442V
 Voltage  230-240V~50Hz
 Max. load
 10 A,2500 W
 Measurable current
 0.02 A - 10 A
 Line voltage display
 200 V~ -276 V~
 Wattage  0 W - 2760 W
 kWh display
 0.0 kWh - 9999.9 kWh
 Battery  2X1.5V AG13/LR44

ELTO EMA1 Power usage meter New Zealand case rear and label

Logic board

The logic board contains three easily identifiable chips. Standard operational amplifiers: LM324, LM358, OP07C. All have the Texas Instruments logo.

ELTO EMA1 Power usage meter New Zealand logic board

AC board

The earth pin/socket and neutral pin/socket pass through the case.  The phase pin is attached to a wire going to the main board. Unlike the neutral pin/socket and earth pin/socket, there is no direct electrical connection between the phase pin and the phase socket. The phase circuit enters the phase pin, passes through the main board, and then back out to the phase socket.

ELTO EMA1 Power usage meter New Zealand main board

AC Board - Close up of 'W1 Voltage' and 'W2 Current'

ELTO EMA1 Power usage meter New Zealand main board w1 volte

ELTO EMA1 Power usage meter New Zealand main board w2 current

Maybe 'W1 Voltage' and 'W2 Current' are used during manufacturing  to calibrate the device.

Interesting situation

I decided to see if the device display would operate without batteries. The display does not operate without batteries. When attempting to operate the device without batteries I experienced a situation where the attached appliance/load would switch on and off. I repeated this with two different loads.

(a) Standard 40W incandescent bulb
(b) Phillips Tornado CFL "N1537 D8 20W 220-240V~50-60Hz I=90mA WarmWhite 1350lm 67Lm/W Made in China"

The standard 40W bulb cycled two or three times over 20 seconds. After this I left the EMA-1 plugged in for another minute or so and the bulb remained on during this time. The CFL cycled more frequently and made an unpleasant sound while doing so. I removed the power immediately. I repeated the same test with an identical meter and the problem did not occur. I then asked a friend to repeat the same test with his identical meter and he did not experience the problem. I repeated the test again with the first meter and the problem did not occur. I was examining the user configurable over load warning feature around the same time.

Update and possible cause: I experienced a very similar problem again. In this case batteries were installed. The device was plugged in and showing a voltage reading on the EMA-1 but no power was being supplied to the appliance. I tried another appliance this made no difference. The appliance plug felt loosely seated in the EMA-1. I wiggled it a bit. When holding the appliance plug towards the EMA-1 on a particular angle then power was supplied to the appliance. I removed the appliance plug and carefully bent the pins outward by a couple of mm. This solved the problem entirely. I can only guess that the previous situation I experienced where a load appeared to switch on and off in a regular pattern was due to partial contact between the appliance plug and the EMA-1 socket. Still interested to hear if other people have experienced similar problems.

Discuss technical / disassembly


21/02/2011 9:04Robin WatsonI have purchased the EMA-1 and the line frequency starts off as 50 Hz. However, after a day or two, this shows as 53 Hz.

Is the unit faulty, or is this normal to not show the correct line frequency?
01/12/2011 16:59T KiddHi, My EMA-1 stopped working all together the other day, producing a faint burning smell !
The batteries were quite low at this point and may have had something to do with what i found..

When opened, i discovered the resistor R1 had gone open circuit, and had a big black scorched band where colours should be!!

Thanks to your photos, and what was left of R1, i guessed that it was around a value of 10 Ohms. Replacing R1 brought the unit back to life! 

The unit is about 5 years old, but has been in constant use for only the last 6 months, so not really the best reliability !
 08/08/2013 15:52 Brian Sandle R1 has also charred on mine. But the colour in the photo may be black brown black, or 100 ohms?