Identifying the Diode

[sunil21]

Given below is the picture of an Ammeter/Wattmeter I was using.
One day during one power fluctuation it stopped working.
Can anyone identify the diode, it appears to be short.
Is it an inductor or a resistor next to it?

[stj]

Re: Identifying the Diode

it's a diode,
but without looking for markings you wnt know if it's a rectifier or a zener
the green thing is probably a choke.

[budm]

Re: Identifying the Diode

How is this diode connected in the circuit? Can you show the location? It is more likely to be ZENER for this capacitive (using cap as a voltage drops device to lower the AC line voltage to run the unit without using a transformer) power supply.

[sunil21]

Re: Identifying the Diode

I bought this stuff 2 years before on ebay.in. The current link to the item <http://www.ebay.in/itm/ENERGY-METER-ELECTRICTY-CONSUMPTION-METER-VOLT-WATTS-KWH-/190772664843?pt=LH_DefaultDomain_203&hash=item2c6aefda0b>
The price has gone up by 50%. I am not very good with smd but it is ok.
Acutally what happened when the house power consumption went up by a large margin i bought this and connected this to check and it helped me a lot and on one day I was trying to check a power saver and because its pin was loose, power fluctuated and after that this ammeter stopped working.
I opened and checked this and i saw one 78L05( next to this diode) and connected a 5v source to the output pin and the unit started working.
This diode (zener or signal -4148 or?) is sitting between diode (M7 -4007) and 78L05.
78L05 ground is connected to the anode of this diode, whose cathode is connected to the anode of M7.
If I get this diode out of the board , can i expect to see some marking like on the ordinary diode?
(mostly it is difficult to find the track, there is not much on the back side - looking like there is a hidden layer in between )

[budm]

Re: Identifying the Diode

OK, More likely to be 12V 1Watt Zener since typical 7805 needs difference voltage of around 5V between input and out put to regulate. That yellow is more likely to be used as the voltage drops and the out out is rectified by M7 diode.
I cannot be 100% sure unless I can trace out the board.
So if you look the Cathode of M7 it should be connected to that black filter cap positive leg, and also to the input pin of 7805. The Anode side of the M7 should be connected to one leg of the yellow cap, or similar to the attached PDF.

http://www.eetindia.co.in/ART_880064...N_5911b90d.HTM

[sunil21]

Re: Identifying the Diode

Great, It was..... 12v.. I Replaced it a with a new one and it worked. I had no smd so I cut and folded the leads of a non smd zener and soldered , it is working.

Mostly when I see SMD based circuits and wonder "How on earth do I find what is what".
There are you guys with good knowledge and experience.

But the display is not looking good , few pixels missing. I may have to clean the ribbon.

[budm]

Re: Identifying the Diode

Thanks for the follow-up. I use through hole device in place of SMD device when I do not have the SMD version on hand.