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Help with identifying component?

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
25,510
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25,510
That's in the diode test function setting.
In opposite direction is open.

Excellent. So you can determine the common connection, and whether they're common anode or common cathode?

It looks like an SOT-23 case (but verify that yourself) Then get some dual diodes in this package. Their voltage rating should be at least twice the voltage for the relay coil, and they should be rated for a current several times the operating current of the relay coil. I suggested a BAW-56 (I think) preciously.

Be very careful because these dual diodes come in several internal configurations and you need the correct one!

D23 is also obviously a diode. However I can't tell if it's a normal diode or a transient suppression device. Either is possible in this location and size of package. Given that the anode is connected to 0V, I'd grab a meaty rectifier (several amps, 200V)? may not be quite right, but should allow you to run tests.

It may be worth while reading the resistance across the relay coils after you remove the obviously damaged diodes. There is at least the possibility that they may also have been damaged.

It's supposed to be pdfcast.ORG

Damn! Sorry about that.
 

Nhrafan

Feb 21, 2011
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OK.

Thank you.
Looks like I have some work ahead of me. I will get on it either tonight or tomorrow and post back when I have more news!
 

Nhrafan

Feb 21, 2011
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Did a little digging around today and traced out the circuits as best as I could.
This is what I came up with.
Can anyone tell me if these items are definitely diodes, what type and if they are critical in this application?

I did unsolder one and make sure I wasn't tracing anything through any other circuits and such. Also learned I need to pick up a much finer point for the soldering iron to do these.

The reading between the -24V terminal and the pin out plug on the good board is 606 in diode mode. In relation to this, can someone tell me what exactly I'm measuring here? What exactly do you measure on a diode? Ohms?

Hopefully this works....
http://pdfcast.org/pdf/circuit-diagram-plc-control-card
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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25,510
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If that drawing is correct, then the diodes are common anode, and are VERY important.

They absorb the energy that is stored in the relay coil when it is turned off. Without them, a very large voltage will appear on the line connected to the control board. This voltage may kill the controller immediately, or it may take some time. In either case it will be VERY bad.

There appear to be more connections to the 0V line than you show in your diagram (labelled as -24V) and They are probably significant. I am leaning more toward this being a transient absorption device rather than a normal diode.

Maybe someone can decode the markings:

63
2C

that are on it...?
 

Nhrafan

Feb 21, 2011
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Crap.
Is is possible that I damaged the IC chip as well then when this happened?
Would it be possible to remove the damaged diodes, replace the capacitor and the diode attached to the terminal and reconnect this to do a quick test to see if this is the case?

I also assume it's next to impossible to replace an IC chip if it is damaged?
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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Well, you did say that the controller works fine with another board in it, so that means it is OK.

I would strongly recommend replacing the dual diodes before you test it with the controller.

Replacing an IC may vary between trivial and almost impossible.

Just looked at the board. OK, without the proper equipment it would be very hard.
 
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