Original PowerMaster Repair

You may want to post this on the electrical forum!

You won't have to do anything but "plug and play". I use the 135 PowerMasters with a variety of high power transformers. If you have an overload, the PM-1 will trip.

The cutoff device in this PowerMaster is the MosFET transitor that is used to vary the output voltage, interrupt the current to trip the E-unit, and introduce the DC offset to blow whistle (or horn), or on opposite DC offset ring the bell.  This transistor is so sensitive to short-circuit currents that it must protect itself.  That is because only a MosFET transistor is quick enough to have the required speed.

I have only the smaller PM's also (7.5 amp) but I did get a New ZW (as they were then called) and saw that each of it's 4 circuits used the same rating of MosFET for the 10.5 amp outputs.  So you won't have any trouble with derailment shorts.

IIRC, these MosFETs were 35 amp transistors.  But that requires heat sinking (the aluminum plate(s)) adequate for that, and I imagine what's there is only enough for 10.5 amps at most (steady current, of course).  I didn't measure them; the PM plate may be smaller (or not).  For the short circuit currents, the MosFETs are silicon but bonded to a heavy copper slug.  The slug soaks up the heat produced for as much as a full cycle (1/60 second) if necessary, without the temp rise exceeding limits.

Right away you'll see that these MosFETs are actually the device that is protecting the 180-watt brick when a heavy short occurs-- this current can be as high as 110 amperes (77 amperes in the smaller brick, which I measured).  The device in the brick is a light relay contact (rated 10 amps in the 135-watt brick... I took one apart... and as reported here, 15 amps in the larger brick.  The 10-amp is a MillionSpot device from Hong Kong, and is not rated to break more than 10 amps.  These relays are intended only to enforce the limits on running output--10.5 amps and 7.5 amps respectively, not to handle severe short circuits.  Without the MosFETs, a heavy short will eventually either burn the 10/15 amp contacts open or weld them shut.

This situation explains the special plugs on the output of the Lionel bricks.  These can only plug into the various MosFET equipped controllers; or the so-called Lionel Lineside Shack, which contains a relatively heavy contact... the contact alone is nearly as large as the whole Millionspot relay, altho is still small enough to be fast-acting.  The UL Standard 697 was modified to not require the entire protection of these brick transformers to be within the transformers themselves, conditioned on other measures (the special plugs).

Another caveat is that the very first batch of the original PowerMasters lacked the calibrated wire on their circuit board which activated the high current interruption feature of the MosFETs.  These were released to be powered by a postwar ZW through a special cable having an in-line glass fuse.  There was a way to identify these-- by serial number or revision letter, but I cannot recall the number or letter.  Is there anyone out there who still remembers?

[I can open mine to see, but you need to be a machinist to make a tool to get  the cover screws out.  Then you need to know what to look for--hardly practical for all.]

So if you are worried, limit your average running current to 7 amps, and connect the PowerMaster to the 3d rail lockon lug through an inline fuse.  Those fuses were in the European millimeter size (8x20??); I never did figure out the rating, but it's possible that the fuse length varied with the amp rating in this series (they were unmarked, unlike USA automotive fuses).   --Frank

Frank, This is interesting, but when ever I have a short or minor overload on my layout, the Power House breakers trip.  Your implying the Power Master trips first?  G

Based upon what gunrunnerjohn has posted in the past, I would say, just pitch it and go get the new Legacy PowerMaster.  This is the Michael with three kids and not a lot of time on his hands. My opinion might change if I was retired and was looking for something to do.

The PM-1 always trips first for me when used with a PH-1 or any other transformer. The inline fuse has never blown, either.

Not me, The PH 135 or the 180 always trip first.  If the MOSFET is shutting off, how does it reset, how long?  Doesn't make sense you would want the chip to save itself.  That means it was pushed to or near a limit.  I would rather the breaker on the transformer.

 

I can understand why a fuse doesn't blow it is way too slow.  G

If you read my 1st post completely, you'd see that the new Legacy PowerMasters are not an option.  They get their command the same way locomotives do, therefore if I were to put a command locomotive on the track it'd sit there waiting for commands.  I want to be able to run command locomotives conventionally with the Cab-1.  Yes I know, horribly backwards.  But my goal is to have an around the ceiling layout in my bedroom.  The command bases (one TMCC and one Legacy) will be on my main layout in the back room.

Hey Frank,

And now for the long version of your response!

 

See you at York in a few weeks.

You can raise the output current limit of the older PMs by simply shortening the loop of current sensing wire.  Desolder one end of the wire and pull about 3/16" of wire through the hole, and then resolder.  The newer units with the switch accomplish the same thing by switching the values of the resistors in the current-sense amplifier.  I have made this mod to several units.

 

Those .1uF capacitors are across the incoming power bus.  I have seen them blow out.  It could be from an overvoltage surge, or they could get cooked if the current sense wire just below the capacitors is running very hot for some reason.

 

Check the FETS to see that they aren't shorted from Source to Drain.

I was hoping you'd show up Dale.  I'll get this working before I mess with the current output, but I want to make sure I know which is actually the right wire to adjust.  Unfortunately I don't have the unit in front of me.  Could you let me know what it is marked on the PCBA silk screen as?  And as which way to pull it, you mean put it 3/16" out the bottom of the board?  Do you cut the extra off, or do you leave it since the case is plastic and won't short out with it?  Does it matter which side of the wire you do it on?

The main problem with those capacitors is their size.  They must be squeezed into a tight space.

The 180W brick has two time constants - a quick one for gross overloads and a slower one for marginal overloads.

So happens that's another of my hobbies, so I don't have to look too hard.

Sinclair--  Seems like your Powermaster is in good hands.  --Frank

 

 

Okay, an update.  With it being said that the caps were a filter, and that it "should" work without them, I did try it and this is what happened (PH-180 as power, and a PS-1 equipped MTH GP38-2 with lighted passenger car on the track:

 

-Switches in Run and Conventional

When I turn the PH switch on, green light on PM-1 and locomotive marker lamps flash and sounds start.  Then sounds die.  So there is a surge of power to the track when the PM-1 is initially powered.  I try addressing it with TR and pressed 1 thru 9 one at a time and turning the red knob (TR-1 turn red know CW then CCW, TR-2 turn red know CW then CCW,...) and nothing.

 

-Switches in Program and Conventional

Following the manual I slid the RUN/PRG switch to program and push TR 1 Set and then slid back to Run.  Again tried TR-1 and turning the red knob, nothing.  SO I turn the power off.

 

-Switches in Run and Command

Turn the PH on and track power come on, locomotive fire up and passenger car lights up.  Try addressing the PM-1 and nothing.  Pushed the HALT button and power remained on.

 

-Switches in Program and Command

Also tried programing it and nothing.

 

All in all, the red light never came on or flashed on the PowerMaster.  Because even the HALT button was also ignored from the Cab-1, which should of worked even if I didn't have the correct address, I'm wondering if the receiver is bad.  So I need to find if any of my EE or radio friends have equipment to test it as Frank said, unless you have some more info Dale.

Step #1 is to verify that the crystal is properly seated and working.  You can swap a crystal from a Base for testing.  Also check both loop antenna wires.

Any troubleshooting beyond that requires an oscilloscope.  Using the schematic, look for the uC's oscillator (fairly small signal) and the output of the Data comparator - TP4.

The two wires are still attached to the PCBA for the antenna.  I didn't think to swap the crystal.  I'll try that next.  I don't have an oscilloscope, so that may take a while to get tested.