Do I HAVE to desolder the diode on a coil in order to test it?

Shavenyak

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Do I HAVE to desolder the diode on a coil in order to test it?

I'm having a couple of fuses blowing and I've started checking diodes. I've checked a few on switches (still soldered on) and they're coming up good. I have two coils, however, with diodes that are reading bad. Do I need to unhook one end of the diode on a coil to determine if it's good? It looks like such a pain, I'm almost willing to just put a new coil on it, but I hate to just throw money at the problem.
 
Yes, you need to desolder one end or the other.

Otherwise, you'll simply be measuring the coil, which is a much lower impedance than the diode.
 
If you want to be in this hobby, you better learn to 'suck it up, buttercup'. ;)

I learned recently that you even have to take some resistors out of circuit to test them
 
The resistance of the coil is much lower than the diode so you'd have false readings.

You must lift one end of the diode to test it.
 
Think of it this way...

The diode is a semiconductor device that reads lower in one direction than in the other. It allows current to flow one way only - provided you don't exceed its ratings and short it out.

The coil is a single piece of wire. Granted, it's wound around a form, but it's still a single piece of wire.

Which will read lower? The single piece of wire or the diode?

This same effect will cause many other devices to read bad while in circuit such as horizontal drive or horizontal output transistors.

When reading other devices in a circuit you will read through the path of least resistance. That is why you get false readings on transistors, diodes, resistors, capacitors, and other things in circuit. You can't always test components successfully in circuit because of this.

Use your 5 senses to help narrow down the problem. (Yes, I know you won't "taste" a diode, but the sense of taste/smell are VERY closely related)

Does it look funny? (discolored, cracked, burnt, bubbled, etc...)
Does it smell funny? (burnt, "hot", etc...)
What does it sound like? (Sizzling, squealing, buzzing, cracking, popping)
What does it feel like? (Finger blistering hot?)

Many times you can short circuit the troubleshooting process by doing this. Rather than look all the way through the circuit, look for and fix the obvious things first before digging deeper.

If you have a fuse being blown, look for the cracked/burnt diodes or coils/relays that are darkened by heat first before desoldering diodes to test.

RJ
 
If you want to be in this hobby, you better learn to 'suck it up, buttercup'. ;)

I learned recently that you even have to take some resistors out of circuit to test them


LOL

I hear 'ya. What about diodes on the switches? I would think it would be okay to test them without removing?
 
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