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Diodes


Beast

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Yep....just fixing a pin and some diodes are attached different ways...didn't notice any probs on the switch matrix but also not sure whether these switches were working in the first place as some wires were disconnected on several switches and some switches missing.
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Does the banded side of the diode always go to a non-wired lug on a microswitch??

 

I say the NON-band faces the microswitch, IE the band goes to GND Wire

 

Are you doing something like this?

 

http://www.dsbelec.iinet.net.au/DiodeM-Sw.jpg

Edited by dezbaz
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I say the NON-band faces the microswitch, IE the band goes to GND Wire

 

Are you doing something like this?

 

http://www.dsbelec.iinet.net.au/DiodeM-Sw.jpg

 

Dez, no, the diodes are part of a matrix so the diode actually goes across the switch to allow scanning.

 

In answer to the OP, it does not matter to the switch which way the diode goes on, but it does to the wires on the switch. [as a switch is not "polarized" the wires may have been swapped at some point]

 

That means, make sure you replace the diode AND wires the same way on a new switch, and all will be well. [a footnote: usually they will have tried to keep to a wiring standard in the factory so what you say is correct, however you have no idea if they may have swapped wires due to a wiring change at the factory, or because some op "fixed" it but may have swapped the wires on the switch too]

 

Worst case scenario, if you get the diode in the wrong way you will get a diagnostic error of a shorted row/column. It will not blow up/short anything, just cause problems reading the switches until you get it right.

 

If you are replacing more than 1 diode, then you MUST get it right, if only because it will be a royal pain in the ass to figure out which one (or more) is wrong!

 

Cheers

Jacob

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Dez, no, the diodes are part of a matrix so the diode actually goes across the switch to allow scanning.

 

In answer to the OP, it does not matter to the switch which way the diode goes on, but it does to the wires on the switch. [as a switch is not "polarized" the wires may have been swapped at some point]

 

That means, make sure you replace the diode AND wires the same way on a new switch, and all will be well. [a footnote: usually they will have tried to keep to a wiring standard in the factory so what you say is correct, however you have no idea if they may have swapped wires due to a wiring change at the factory, or because some op "fixed" it but may have swapped the wires on the switch too]

 

Worst case scenario, if you get the diode in the wrong way you will get a diagnostic error of a shorted row/column. It will not blow up/short anything, just cause problems reading the switches until you get it right.

 

If you are replacing more than 1 diode, then you MUST get it right, if only because it will be a royal pain in the ass to figure out which one (or more) is wrong!

 

Cheers

Jacob

 

the only thing i would add to this is that the way it is before you touch it is not always correct. I have had two machines that have arrived with diodes wired incorrectly, it plays hell with the switch matrix. its a good thing to check if the closure of switch 46 is registering as switch 64...

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TESTING SILICON DIODES (NOT LED OR ZENER)

To test a silicon diode such as a 1N914 or a 1N4001 all you need is an ohm-meter. If you are using an analog VOM type meter, set the meter to one of the lower ohms scales, say 0-2K, and measure the resistance of the diode both ways. If you get zero both ways, the diode is shorted. If you get INFINITY both ways, the diode is open. If you get INFINITY one way but some reading the other way (the value is not important) then the diode is good.

 

If you use a digital multi-meter (DMM), then there should be a special setting on the Ohms range for testing diodes. Often the setting is marked with a diode symbol:

 

Its always advisable if you are new to this, to have the power turn off.

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TESTING SILICON DIODES (NOT LED OR ZENER)

To test a silicon diode such as a 1N914 or a 1N4001 all you need is an ohm-meter. If you are using an analog VOM type meter, set the meter to one of the lower ohms scales, say 0-2K, and measure the resistance of the diode both ways. If you get zero both ways, the diode is shorted. If you get INFINITY both ways, the diode is open. If you get INFINITY one way but some reading the other way (the value is not important) then the diode is good.

 

If you use a digital multi-meter (DMM), then there should be a special setting on the Ohms range for testing diodes. Often the setting is marked with a diode symbol:

 

Its always advisable if you are new to this, to have the power turn off.

 

excellent explaination, I understand exactly what to do now. I wondered what that symbol represented on my mm. I think the better mm's this setting also buzzes?? I can try this out as I have been told a problem I have may be a shorted diode, so now I can test this out. Thanks heaps

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