TIU variable channel 2 high voltage

Power FET is probably shorted.  G

Exactly what meter and meter setting are you using to measure the output voltage? 

Apparently you are measuring 18V AC at the TIU VAR2 input and 45V AC at the VAR2 output?  The TIU does not have the ability to "boost" the AC voltage so as GGG says there is likely a component failure in the VAR2 circuit.  Such component failures can alter the AC signal in a way that causes hobby-grade meters to incorrectly indicate abnormally large AC voltages.

Thanks for the response, is there any thing I can do?  Simple complicated, expensive.   What's is FET?

Solution: email GGG.  He repairs them, and does it well.

We have had the same issue on 8 Rev L TIU's  It is definitely the power FET  ( Field effect Transistor)    It uses small amounts of power to control larger amounts of power     It will read 45 volts with no load but as soon as you put a load on it the highest it will go is 10-12 volts.  The FET is a little component on the TIU board that is a major pain in the butt to change   Much easier to have George do it   According to MTh and BArry they haven't seen this problem and it was probably user error which I think is baloney.

That's awesome, don't really know the site how do you email?  I click on GGG but there was no where to email.  Again thanks y'all are great.

bluelinec4 posted:

We have had the same issue on 8 Rev L TIU's  It is definitely the power FET  ( Field effect Transistor)...

8 units?    Did you guys come up with a conclusion on the cause?  And/or did you come up with some kind of added protection?

Bryan posted:

That's awesome, don't really know the site how do you email?  I click on GGG but there was no where to email.  Again thanks y'all are great.

My e-mail is in my profile down on the bottom right.  Yes this can be fixed.  G

Bryan posted:

... is there any thing I can do?  Simple complicated, expensive.   What's is FET?

Best bet is send it to GGG.

The FET itself is not expensive (about $1-2) and they are readily available mail-order.  You can read the part number right on the device.  There are 4 FETs per Variable channel - photo below shows each FET screwed to a heat-sink.  There is a logical process on to how to repair it.  GGG knows all this.

Some guys have just replaced all 4 FETs with success.  Call me cynical but I figure you only read the success stories!  I assume there were cases where a DIY repair was attempted and things went south...

Bryan posted:

That's awesome, don't really know the site how do you email?  I click on GGG but there was no where to email.  Again thanks y'all are great.

GGG's email in his profile won't be a link, you will have to copy and paste it into your email program. If you haven't already figured this out that is.

Replacing all the FET's will certainly work, but you can also test the FET's.  Truthfully, in many cases, I just shotgun it and replace them all.