Hello, I'm very new to electronics and i know this question is very basic but can somone please tell me what this part is? The owner of the board put 230v sc across the terminsls that were only supposed to get a volt free contact. Thanks in advance. Gary
I can measure a good one and get the following readings
4.77 k ohm resistance

On diode test, 0.59 v with common probe on left and red probe on right
1.35 v with leads reversed

 

Hello, I'm very new to electronics and i know this question is very basic but can somone please tell me what this part is? The owner of the board put 230v sc across the terminsls that were only supposed to get a volt free contact. Thanks in advance. Gary
I can measure a good one and get the following readings
4.77 k ohm resistance

On diode test, 0.59 v with common probe on left and red probe on right
1.35 v with leads reversed
View attachment 191661

From what i can make out the part has M K 5D on it.

 

Welcome to AAC.

That is a diode. I don’t recognize the manufacturer, perhaps someone else does.

The markings on the diode ”5D” match the markings for several manufacturers diodes.

It should not conduct in the one direction at all, so it may well be damaged.

 

Welcome to AAC.

That is a diode. I don’t recognize the manufacturer, perhaps someone else does.

The markings on the diode ”5D” match the markings for several manufacturers diodes.

It should not conduct in the one direction at all, so it may well be damaged.

Thank you
On diode test i get 1.35 volts one way
And 0.59 volts the other way
??

 

You are giving VERY little information for any of us to help diagnose the problem. (I am assuming "230v sc" should be "230v ac")
What is the function of the board ? What is the intended function of the two terminals ? Some kind of relay or opto isolated switching input or output and what are the expected signal level to these terminals ?

Les.

 

Those aren’t good readings for an intact diode, but, the diode is in-circuit and so your measurements may be influenced by other components. The only way to be sure is to desoldering the diode from the board and test it.

Wby do you suspect the diode is bad?

 

You are giving VERY little information for any of us to help diagnose the problem. (I am assuming "230v sc" should be "230v ac")
What is the function of the board ? What is the intended function of the two terminals ? Some kind of relay or opto isolated switching input or output and what are the expected signal level to these terminals ?

Les.

Thanks les.
The circuit board is out if a boiler.
The terminals where the fault occurred are to switch the boiler on and off from an external volt free contact. The owner put 230 volts ac on these terminals...BANG!!
Sorry the information I'm giving it's not very good.
Thank you all for the advice

 

Knowing that high voltage AC was applied in the wrong place, and that there was a bang, I would first look for “skid marks”, that is missing components leaves a mark or components with cracks and black around them.

 

Those aren’t good readings for an intact diode, but, the diode is in-circuit and so your measurements may be influenced by other components. The only way to be sure is to desoldering the diode from the board and test it.

Wby do you suspect the diode is bad?

The readings im giving are from the same type close by on the board.
The damaged one has the following readings
On diode test 0.000 volts ( i think thats a short circuut) ?
On resistance ive only 0.3 ohms
Thanks for the help

 

The statement "from an external volt free contact. " means that no external voltage should be connected to either of the two terminals. They would be connected together (By a switch contact or relay contact.) to probably the ON state and the would not be connected together to probably give the OFF state. (It could work the opposite way round.) This is bad news as the terminals probably connect directly to logic level circuitry with little or no protection. Looking at the picture it looks like a track between the left hand connector and the diode has vaporised (Acting as a fuse.) You will need to trace out the schematic of the area connected to those terminals to understand what damage is likely to have been done. The fact that the diode has gone short circuit MAY mean it has protected the rest of the circuit.

Les.

 

The statement "from an external volt free contact. " means that no external voltage should be connected to either of the two terminals. They would be connected together (By a switch contact or relay contact.) to probably the ON state and the would not be connected together to probably give the OFF state. (It could work the opposite way round.) This is bad news as the terminals probably connect directly to logic level circuitry with little or no protection. Looking at the picture it looks like a track between the left hand connector and the diode has vaporised (Acting as a fuse.) You will need to trace out the schematic of the area connected to those terminals to understand what damage is likely to have been done.

Les.

I concur that the trace is missing and with some luck, that trace and the diode it runs to will be the only damage. It’s possible but I don’t know how likely. If it was me, in the absence of other skid marks elsewhere on the board, I would repair the trace, replace the diode, and test.

 

ommon probe on left and red probe on right

how you know it outputs + to red(X) and - to black(COM)
the first match google gave for is listed 1-st for some while . . .