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VARIAX 500 PCB assistance needed.

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Fried the diode and another component on the power input of my pcb.


would like to know the value of this diode if someone from L6 sees this request.

also need to know the part/value is, of I7 that runs between the power input and the negative side of C111

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Not quite so in this case,... 

Typicial diode drop is due to trying to run VDI with battery still inside.

But yeah, that too what Charlie said, only way fewer incidents of that.


And depending on which diode,.... no, not any diode will do.

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  • 2 weeks later...

PIV (peak inverse volt) spec has to be correct, or it will blow again.

Current is trying to flow the other way.


Take the battery out before plugging into the VDI cable.


Er... what? 


Are you saying that if one is plugging in a VDI cable---say, to run to a Helix, or POD HD500---I need to remove the battery box from my Variax 500?


If so, that might merit a mention in the manual and maybe a service alert to owners. It's sure not in the currently available Pilot's Guide for the Variax 500/700.

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1) No, it's not BS. It's been the case with early Variax since before I came to Line 6.


"The Diode blows if you ever try to plug in the battery backwards"---

2) Yeah, backwards batteries will do it too.


"Specs on that diode should not be critical at all"---

3) Wrong. Exceeding PIV blows diodes, that's why diodes have a PIV spec in the first place,

so that you know not to go beyond that.


Pulling batteries when using VDI is even more important with the 700 Electric.

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Diode is a one way valve. Peak Inverse Voltage (PIV) is the maximum voltage that

can be sent in the inverse direction before the diode fails. Too much voltage beyond that,

and it overwhelms and breaks down the volt barrier,... and the diode fails.

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Some basic ones have 75V PIV.

But that also assumes volts coming from one side of the diode at a time.


Battery AND an XPS or VDI,... at the same time,... volts coming from both sides of the diode,

while the diode is on,... poof! Failed diode.


Even worse for Schottky and Germanium diodes.

It's not going to handle volts from both sides at the same time. Same with the 700 Electric.

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Diodes don't take sides.  There is either a forward voltage (diode is conducting) or reverse voltage (diode is off).  The reverse voltage rating is typically at least 100V on any general purpose silicon diode.  Forward current of 1 Amp is typical and more then enough for that application.  You are making much more of what that diode does than necessary.

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When the diode conducts and you have voltage build up coming the other way in

a circuit, while the diode is on (conducting), as in volts from VDI one way and battery

volts from the other,... there is an opportunity for the diode to fail. And it usually does.


I've seen it happen. Used to do this in school as a test to see how diodes fail. It's why

700 Electric boards were later revised. 

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