Class lights not working on southern pacific PS2 PS-4

@DashingDanLIRR posted:

Hi all,

I picked up a broken Pacific PS2 PS-4 on ebay for $100. I replaced the broken part which was the drive block and the engine is running great however I noticed the class lights on the front aren't lit. (headlights, smoke, firebox light, all work)

I reset the engine using the 1W5B method, reset in DCS with a factory reset. replaced the LEDs with new LEDs, so now I'm left to believe that the MUX board is the problem.

If anyone has any suggestions for what to try/check or if anyone has a spare MUX receiver board they are looking to sell (none are available on mthpartsandsales) please let me know!

Thanks,
Dan

FWIW, in some engine sound files, the lights are not on by default!!!

In other words, if you reset thinking by default after a reset they are on- did you actually go in and toggle on/off the class lamps in DCS?

I've seen this in one or more customer engines before.  They come to me for some repair, as a process, I check in DCS and then always reset the engine, but then also check in conventional after the reset- and that's when I caught this "OFF by default" behavior.

Part2 LED being polarity senstive, it's possible either the LEDS or wiring harness is reverse polarity- have seen that once or twice.

The catch 22 is, Mux engine side boards have long, long, long been out of stock. You would have to repair it by replacing the tiny surface mount failed transistor(s).

So yes, there is a good chance this is one of the 2 above errors- off by default in software, or reverse polarity from someone replacing them trying to get them to work.

I assumed the file was correct since the LMK/LNS buttons were working and correct, how do you turn on/off the class lights in DCS?

As far as polarity goes I bought new class lights from MTH and installed those so I don't believe its a polarity issue but I'll double check the connector.

Any idea which transistor would control the class lights?

Thanks,
Dan

The markers are on the "more" menu.  Unless something has shorted the lighting output to the frame, the mux board doesn't often fail.  It should be pretty simple to trace from the marker light pin on the 7-pin connector to the FET that controls the markers.  That would be pin-6, and the FET is an N-channel SOT-23 part.

Did you actually test the markers independently using a resistor and DC supply?

The markers on the tender are working, and via the dcs menu, the class lights on the boiler cover aren't working.

I didn't test the LEDs directly, i assumed a new set wouldn't be defective, are these 3.3v or 5v leds?

Thanks,

Dan

thanks @gunrunnerjohn and @Vernon Barry for your help! out of desperation i took a multimeter to the outputs and im getting 0V, I'm going to chalk it up to a bad MUX receiver board. for now its a PS-4 for 100 that runs perfectly except for the class lights so I'll ignore it (nothings ever perfect on a railroad). Maybe I'll come across a replacement mux board at some point that I can replace it with. My soldering skills are....poor so I'm not going to attempt to replace an SMT FET.

Thanks again!

Dan

Drop me a line, I have mux boards.

@gunrunnerjohn sent you an email, thanks!

-Dan

It's on it's way, or at least in the box with a shipping label.

Where else can you find technical knowledge and the willingness to help like this?  Eight hours after posting, and you have an answer and a part ready to be shipped! 

Beside mux board issues, it can be wiring break, bad solder joint at the 2 pin connector. Polarity issue if someone used wrong LED type.  G

Obviously the OP wants the lights working, but in reality class lights were not used on scheduled trains and were used at night, flags were used in daytime.  Extra trains ran white, multiple section trains had green which denoted another section following .  I wish all the class lights were off and lit only by command.