Power Master

Believe there is one piece that blows out and causes it to go into full voltage mode.

Bet our OGR Forum repair guru's could fix it.

I think Dale Manquen might be the person you need to talk to. Maybe he will see this and reply.

Just a thought here, and I don't know a lot about all the Lionel stuff (Power masters being one of those 'stuffs'), but with all the good things that were said about the new Legacy Power masters an upgrade might be worth while?

Cheryl, email sent.

I have 3 others, I was just curious as to whether this would be repairable.  Thanks for the input guys.

The triac croaks in those and causes that failure I believe.  It's certainly replaceable.

Ok, GRJ, that's cool to know.  Now, just what is a triac? lol

The triac is the component that controls the power level, it's the usual suspect when you get a symptom like this.

If the Emergency Stop key doesn't kill power through your PM, then one or both of the output FETs (not triacs) is shorted. 

If the key does kill the output, you may have the minimum voltage function set incorrectly.

By chance did you look at the switch on the side of the PM.  Conventional or CMD mode.  Command mode is straight 18Vs.  May just be a switch setting.  G

Dale, I thought the old PM used triacs, my mistake.  In any case, the output device would be the culprit.

You would only need one Triac, as in the case of the TPC.  All of the FET stuff requires back-to-back FETs.

I didn't actually open one up, I just assumed based on the age of the design.   if I ever need to repair one, I'll check the numbers on the part.

Dale,

Isn't there a spike protector device that was used on some of the power masters. This part was prone to failure, too. I believe at one point you recommended a device with a higher rating?

I only found one TVS installed, and it was exploded and charred - an open circuit.  Since that TVS is across the FETs, not the input or output, I suspect that the transformer voltage was too high for the TVS rating, and when something shorted on the output, the transformer voltage was across the TVS.  Unfortunately, I couldn't determine what rating Lionel used for the TVS in the first place.

I have even seen a unit with the current-sensing wire loop melted away!  That must have been a spectacular overload!

While back at the ranch....,  Cheryl did you look at switch position by chance?  G

G,

Yes, I tried all possible combinations of switch settings just for giggles and no change.

I don't remember if the E-stop killed power, will have to check that and let you know.

Thanks guys.