TIU Rev L - Variable vs Fixed channels - Reliability or Robustness differences ?

Well, the fixed channels have the same vulnerability to voltage spikes damaging the DCS signal generator, but the variable channels also have the FET drivers that carry power even in fixed mode.  So, given there are more components that can fail, it makes sense that the fixed channels would likely be somewhat more resistant to the ills that can befall electronics, less electronics in the path.

Edit: fixed typo!

gunrunnerjohn posted:

Well, the fixed channels have the same vulnerability to voltage spikes damaging the DCS signal generator, but the variable channels also have the FET drivers that carry power even in fixed mode.  So, given there are more components that can fail, it makes sense that the variable channels would likely be somewhat more resistant to the ills that can befall electronics, less electronics in the path.

Thanks for the information John.

Two more questions:

1) Should I understand that, to the exception of the FET drivers on the Variable channels, the rest of the circuitry is identical on all 4 channels ?

2) Are those FET drivers on the Variable channels known to be fragile ?  i.e. is it common to see those failing ? (still in the context of operating in "FIXED MODE")  

Don Merz 070317 posted:

GRJ I think you have a typo here that reverses what you intended to say. I think you meant to say that the FIXED channels might be less likely to have problems because there is less electronics to fail. Instead, your last sentence makes this claim for the VARIABLE channels. Right

 Thanks, I corrected that, wrong word used!

Daniel Auger posted:

Thanks for the information John.

Two more questions:

1) Should I understand that, to the exception of the FET drivers on the Variable channels, the rest of the circuitry is identical on all 4 channels ?

2) Are those FET drivers on the Variable channels known to be fragile ?  i.e. is it common to see those failing ? (still in the context of operating in "FIXED MODE")  

The output stage looks to have most of the same components for mixing the DCS signal into the track feed, so that's pretty similar.  Besides the driver FET's, there are some other gate components in the variable channels, but the most common failure item is the output FET's.  The output FET's are a fairly common failure, and they're certainly more fragile than the relay that cuts power in the fixed channels.

Thanks for the additional information GRJ.  It does answer my questions.

Define fairly common please?  As techs we get stuff that fails, but we don't get told how many customers have TIU with no failures?

I keep records of expended parts.  I have replaced 12 receiver chips, 21 installed TVS diodes, 22 Var Channel FETs and 53 Transmit buffers since about 2011. 

This is the vocal part of the hobby on the forum.  Need to be careful of data.  I do not get many TIU back even those without TVS mod.  G

GGG posted:

Define fairly common please?  As techs we get stuff that fails, but we don't get told how many customers have TIU with no failures?

I keep records of expended parts.  I have replaced 12 receiver chips, 21 installed TVS diodes, 22 Var Channel FETs and 53 Transmit buffers since about 2011. 

This is the vocal part of the hobby on the forum.  Need to be careful of data.  I do not get many TIU back even those without TVS mod.  G

Considering the context of my initial question:  "There is a belief at our club that the two real Fixed channels are more reliable or more tolerant to shorts, spikes, etc..., than the two Variable channels.  Myth or reality?"

In general, have you observed more "expended parts" associated with the Variable channels ?  (The count of "22 Var Channel FETs" replaced seems to suggest that it is the case, even if the overall failure rate is low)

As Danial says, I was just comparing the fixed to variable channels, not trying to do a statistical analysis of TIU failures.   FWIW, I've probably done the 1500W TVS replacements most, followed by the transmit buffers and FET's.  I have yet to have to replace a receiver chip.

I'm not a repair guy like John and GGG but I do own the L.  I got it when it first came out,whatever year that was, but it was a while ago.  I use the VAR channels in both modes, varying from year to year.  I have never had an issue with any component in my L.  

A plug for the positive side!

walt