TMCC Lionel direct lockon

I just opened one up.  If it has it, it's really well hidden, I don't see it in there.

Thank you for doing that. Much appreciated. I wll pick some up at the local electronics sore store. Thanks again...Jeff

I think I better put some in mine as well.   Now that I've looked, I sorta' thought they'd have them as well.

I am new to the forum but have been reading non stoop it seems for the past week. I am fairly familiar with running DCS and Legacy so I understand most of the topics. I also see you post replies very often and they have been very helpful to me. I notice that many also put a TVS in each loco.  Is that overkill?  I actually have 5 legacy units in transit to Lionel for warranty work. All the problems are with smoke units and two of them have the three blinking cab light syndrome. I have talked with Lionel and explained my power source, breakers and track wiring. They say its all ok..the smoke unit problems did not happen all at once. It happened over last few months and I just decided to send all back at once. I know their smoke units have problems but 5 locos going bad seems excessive. Could not having a TVS led to this?  My Legacy E6 Pennsy Atlantic is on its fourth trip back. Last time they changed both smoak units and a board or two, not sure which ones.  

I was not done writing and I hit the "submit" button. Sorry. I wanted to add that I get the feeling  I am the cause Of at least some of the problems. I also have been running 4 MTH units with smoke during same time period and there have been no issues at all. I prefer the Legacy over MTH by far anyway. I run them almost daily for a few hours. 

While others have a different opinion, I feel that a TVS in each locomotive is not overkill.  I designed cockpit instrumentation and fuel systems for commercial and military aircraft for years, and the basic rule of thumb was always to put the transient protection as close to the protected load as possible.  Every input to an electronic system has transient protection, usually right on the PCB involved.

Whenever I open up a locomotive for other maintenance, I add a TVS if there isn't one there.  There's no downside that I can see to having the protection, and it hasn't affected the operation of any of them.

Gunrunner,

Could you please explain what a TVS is and does for an electrical neophyte like myself?

Joe

A TVS is a pair of zener diodes that clamp voltages over it's rated value.  So, in the case of the 36 volt TVS we're normally talking about for O-scale trains, voltage spikes over 36 volts would be clamped to the common lead.  For voltages under the rating, the TVS is basically not there except for some small stray capacitance and micro-amps of leakage current.  Obviously, the rating is not exact, so 38 volts might get through, the idea here is to clamp the spikes of hundreds of volts that can some through and kill the electronics.

Being new to the train world can anyone speculate why lionel hasn't designed any TVSs into their products.  It just makes sense!  Seems stupid in my own paranoid way, but is the reason not to have these, a means of keeping the economy going???

No idea why Dave.  I'd think that all the makers would be installing them in locomotives and tenders with electronics.  I guess the extra ten cents they'd have to pay for the extra component is too much to create a more reliable product.

I suspect that Lionel got burned when they installed an undersized TVS in one version of the Powermaster track power controller.  I have seen evidence that the TVS would fail as a short or explode. 

For a while, Lionel just didn't stuff the TVS on the board, and eventually they dropped the provisions for the TVS altogether.

When I repair a Powermaster, I install a TVS in the same location, but it is a much larger TVS than the original version.

By "much larger", which specific part do you use?  To the TPC's have a TVS?

I use the common 1.5KE part that we recommend here on the Forum.  I believe the original Lionel part was the 600 watt version, rather than our 1500 watt version.

The TPC has a terrible design.  It has a small TVS directly across the input power feed to the logic power supply, but there is no resistance in series to provide any "voltage compliance" in the event of a surge.  The surface mount device gets hit with the full surge and easily self-destructs.

I have had to repair a few TPCs with significant damage to the TVS, rectifying diode, capacitor and voltage regulator.

I guess that means I should probably use a real TVS with that one too.   I see your point about the series resistance, I'd be tempted to add a low value choke except it would have to be pretty big for a 15A or more load.