K-Line Plymouth Switcher Smoke Design Mistake!

gunrunnerjohnOGR Forum Member SUPPORTING MEMBERDIGITAL SUBSCRIBER

I was looking at the smoke unit from a K-Line Plymouth switcher, the fan refused to run. The motor was good, it drew around 30 milliamps at 5VDC from my bench supply. When I measured the voltage, I got about 4.5V from the 5V supply. That's a bit odd... When the motor was attached, the voltage dropped down to under 2 volts and the fan didn't run.

On closer examination, I found out why! K-Line screwed up putting the three components for the fan power supply together! The filter cap in on the output of the regulator instead of the input! Initially, I couldn't figure out why a 100uf 10V capacitor hadn't exploded when running from track power, usually the input filter cap sees at least 20-25 volts! When I looked closer, I realized it was wired to the output of the regulator and not the input side. Of course, the 5V regulator doesn't regulate properly without an input filter cap, hence the odd behavior of the output voltage.

A simple chop of the PCB and a jumper wire, and the fan was back in the game. I'm curious, has anyone else run across this issue? It's hard to believe that was the only example since it was a finished PCB on the smoke unit.

9/6/2210:36 AM

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KeystoneOGR Forum Member

@gunrunnerjohn Curious if this was an across the board design error or just a limited factory production run defect. Is the wiring/assembly of what you found consistent with other K/L Plymouth switchers since they were produced over several production cycles in both individual units and specialty sets? Did K/L use the same or similar smoke unit design w/ their little Porter engines that were produced during the same period?

9/6/2211:22 AM

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RSJB18OGR Forum Member SUPPORTING MEMBERDIGITAL SUBSCRIBER

John- I have 6 Plymouth's, all purchased used, so I can't say what period they each are from. Smoke works well on all of them.

Guess you got one that was done on Friday afternoon.....

9/6/2211:26 AM

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Vernon BarryOGR Forum Member SUPPORTING MEMBERDIGITAL SUBSCRIBER

I might have run across this myself in the past and maybe forgot about modifying the circuit. FWIW, I have seen problems on other locos where I converted to TMCC and fed a traditional 27 Ohm fan driven smoke unit from the TRIAC output of an R2LC and was frustrated the more DC biased output of the R2LC would not run the fan.

Again, I'm sure if have seen exactly what you describe, bulk capacitance on the output instead of the input to a regulator and probably was a certain K-line Plymouth.

9/6/2211:27 AM

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gunrunnerjohnOGR Forum Member SUPPORTING MEMBERDIGITAL SUBSCRIBER

@Keystone posted:
@gunrunnerjohn Curious if this was an across the board design error or just a limited factory production run defect. Is the wiring/assembly of what you found consistent with other K/L Plymouth switchers since they were produced over several production cycles in both individual units and specialty sets? Did K/L use the same or similar smoke unit design w/ their little Porter engines that were produced during the same period?

As for the questions about the flaw, this was a design error in the actual PCB layout, not a wiring error. The PCB looked brand new, and probably was since the smoke didn't work!

Yes, I have a number of K-Line Plymouth engines, and all of them smoke fine. This was the first time I saw this, the fact that it was designed into the PCB struck me as very odd, how did they manage to test this design?

The Porter and Plymouth used different design smoke units, though they were similar.

Porter on the left, Plymouth on the right. Lionel lists only the PCB for the Plymouth, that PCB looks just like the one I modded, the fix was on the underside.

I believe the diecast "tank" is the same, the Plymouth uses that top hole to exhaust the smoke, the Porter uses the end.