NO BODY MARKING Diode

[dennis_elx33]

Hello Everyone,
I have 1 diode on a circuit that I suspected to be faulty because the forward and reverse bias has a voltage drop reading.
While compared to the reading of another diode from the next channel it won't read at reverse bias.
Now the problem is; it does not have any body marking.
So I tried to sketch the diagram and found out that it is connected to the base and collector of the C3632 transistor.
What do you think is this diode?
Can you please suggest what part number can i use to replace this faulty diode instead?

Hoping that you can help me on this.

Thank you so mch!

[harp]

This is likely to be 1N4148, small glass signal diode, very common, and probably not your problem - failt diodes tends to be shorted.
The silk screen have symbol of diode and marking D.

[lotas]

It is soldered in parallel to the transistor (this is the result).... If in doubt, you need to raise at least one pin and check it in the circuit.

[harp]

This is likely to be 1N4148, small glass signal diode, very common, and probably not your problem - failt diodes tends to be shorted.
The silk screen have symbol of diode and marking D.

[dennis_elx33]

lotas yes, i removed it already and measured stand alone. Also have tried to inject voltage to check if it is a normal diode or zener diode. But it seems that it is a normal diode because the voltage drop i read versus the voltage supplied is still same even i injected up to 6VDC already.

[dennis_elx33]

harp thank you so much! Will try your suggestion out😇 by the way, is there any risk if i use the 1N4148 directly and test the unit at the machine?

[harp]

I dont know, probably not shuld be any catastrofic risk... but, if you tested your diode out from circuit, and it is good, I suggest you that you put back like it is be.
If on pcb find only one mark ZD or symbol of zenner on silk screen, that mean that for sure your diode is not zenner. Zenner diode in glass package often have colored ring or two, like yellow, green or so...

[lotas]

The silk screen have symbol of diode and marking D.

Not all companies designate zener diodes on boards with the symbol Z, ZD.., they can all be designated D (in my opinion, a 7.5v zener diode is designated as D.

[harp]

Lotas, nice catch!

[dennis_elx33]

Thank you so much guys!
To make things clear, I attached herewith the images of the faulty diode (channel 1) versus the good diode (channel 2).

[CapLeaker]

Not all companies designate zener diodes on boards with the symbol Z, ZD.., they can all be designated D (in my opinion, a 7.5v zener diode is designated as D.

This is correct. I noticed that a long time ago as well.

[kasfamily]

Yes, there were times before and all the details were marked on the board.

[harp]

Yes, the diode is faulty. Have you noticed what Lotas pointed out, that on other diode is marking "7.5", so if you check with supply, voltage must be higher than 6v. Normaly zenner tester have about 50v and 1 or 10mA on probes.
Check, maybe your faulty diode has marking oriented to pcb side?

[R_J]

Any chance that you could provide the Make and Model ? or what equipment this board is used in?

[dennis_elx33]

Hello R_J, attached herewith is the photo of the board.

[dennis_elx33]

Hello All,

I was trying to post a new thread but i couldn't find the button for a new thread.

Anyway, i would like to post an interesting topic regarding 3-phase stepdown transformer which we suspect to cause an overcurrent (138A) which caused the High voltage power supply to tripped off.


Problem statement: Power tripped with inrush current of 138A.
Initial findings: low ohm L2 to L3 input voltage (25ohm)
Defects: IGBT and Diode shorted

Question: is this a normal resistance reading for the transformer at L2 to L3 reading?

Red Probe	Black Probe	Reading
L1 ( P7)	L2 (P6)	51.29K Ohm
L1 (P7)	L3 (P8)	51.31K Ohm
L2 (P6)	L3 (P8)	23.3 Ohm

[R_J]

The DC resistance of transformer windings can be low resistance.
It looks like a single tapped primary, so it will be connected across one phase of the three phase likely between L2 and L3, I suspect there is a line voltage select switch somewhere as well to switch between 208, 220, 240 input

one phase should connect to 0 on the transformer and one of the other phases should connect to one of the taps on the primary depending on the a/c voltage of that phase (likely 240 in your country)

Maybe a mod can move this to a new thread for you

[kasfamily]

Hello All,

I was trying to post a new thread but i couldn't find the button for a new [/ATTACH]

…

[dennis_elx33]

Hello R_J and kasfamily thank you so much..I will post it in a new thread..i will add some update as well.