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I have a Premier Blue Comet Steam as well as a RailKing GS4 Daylight, both with failed boiler boards. Is this called the mux board?

Process of elimination and using a board tester for the main power and processor boards has confirmed it is the boiler board that has failed. If plugged into the PS2 3v set it caused garbled sound and constant resetting of the relay. Disconnect the boiler board and the PS2 3v board does all it should.

Can I still get this replacement board?

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Last edited by DdotCdot
Original Post

Yep, I have several of them in stock if you need them.  However, are you sure it's not something connected to the boiler board that's the issue?

That board failure would either be a PV diode shorting or opening, or a fet for lights.   Not sure how you are testing it with a PS-2 3V test set since there is no provision for that.  What is the engines issue when that board is installed.  It is the Receiver MUX in the engine.  The Tender has the transmit mux.

If it has issues usually it is a light problem.  Nothing to do with motion other then it does provide the return for Tach.   G

gunrunnerjohn posted:

Yep, I have several of them in stock if you need them.  However, are you sure it's not something connected to the boiler board that's the issue?

Yes, positive. This board has two Molex connections - 7 and 6 pin. I removed the output connection to the lights etc just to be sure it wasn’t anything post mux and just plugged that board itself straight into its input Lead socket from above the gearbox - as was factory designed. When the mux board is connected, regardless of anything connected post mux, the PS2 board does the following on power up: “TICK TICK......BUZZZZZZ.” (Retry.) TICK TICK......BUZZZZZZ.” (Retry.) ...and so on. I didn’t let that continue too long fearing damage. It’s as if the board keeps trying to reboot following a fault detection. The garbled buzz sound it makes is awful.

Disconnect that board and the PS2 board starts normally: “TICK TICK”....(Start up sound.) (Normal board behavior/sounds.)

GGG posted:

That board failure would either be a PV diode shorting or opening, or a fet for lights.   Not sure how you are testing it with a PS-2 3V test set since there is no provision for that.  What is the engines issue when that board is installed.  It is the Receiver MUX in the engine.  The Tender has the transmit mux.

If it has issues usually it is a light problem.  Nothing to do with motion other then it does provide the return for Tach.   G

I used process of elimination. Removed the PS2 3v and placed on my board tester. Board tested fine. Placed back in tender. Problem. Began disconnecting connections in engine, post mux. Same problem. Disconnected mux. No problem.

its definitely the mux in both locos.

No idea. The daylight was given to me by a previous owner with this problem because he couldn’t figure it out, so I inherited it.

the blue comet is a customer repair

the only thing both had in common was that they are somewhat drenched in smoke fluid. I wonder if this caused the issue. same symptom with both engines, from two different people

First you need to trace the wires to the mux.  If you had no wires plugged into the mux just the 10 pin to the engine chassis plug in the middle of the engine it would be a harness problem.  Does it have the thick blue wire soldered underneath the PCB?  Are the smoke fan and such in the right receptacles on the output side of mux?  SHorting out he PS-2 board with a buzz is going to be a 5VDC or PCB Ground issue overloading the processor.  There is only one chip powered by DC on the board  is it burned?  G

I would agree with George.  You mentioned smoke fluid outside the smoke unit itself.  You possibly have  a PV or P5V issue around or at the smoke unit.  Can you disconnect the PV wire going to the smoke unit and the P5V going to the smoke unit fan without disturbing the other PV and P5V connections?  Check your service manual 4-45 for the MUX wiring diagram.  Try it.

Bruce

267ECC46-9B25-42E7-A586-D75EBB57C85D

well, I think I’ve determined the cause of death to the mux boards. same exact finding in the daylight.

both smoke units look like this one (from blue comet). the wick was completely charred and there was a lot of char stuck between both elements, basically in the form of a fault or short (if it was a piece of wire between them). Fluid everywhere with nowhere to settle.

I strongly believe that either the charred wick at some point carried a current between the elements short enough to blow up the mux, but not long enough to crack the heaters or trip the breaker....ok, maybe a long shot theory. My other, more rational, thought is that the heaters just got too hot for too long with burning wick charring against them and that caused the mux to fail before the elements went too. Either way - a combo of poor factory wicking and lack of proper use.

both heaters did survive. I cleaned off and burned off the remains and both elements work just fine. Tested the heater set independent of the engine with my little handy bench 1033 on 10-12 volts for a few seconds.

did continuity tests everywhere. all wiring was just fine, no faults, no shorts, no broken insulation.

so..... I am going to ditch the lousy factory style of wicking that failed and rewick the way I do all my others that works great. Just slice up the wick to bits and fill up the tray with a nice soft padding of wick for the fluid to drench and be held and for the heaters to smoke. I think someone called this method “Reaganizing?”

Replacement mux boards are on the way...

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I doubt that is the problem.  That is just PV which is generated by the MUX diodes.  But since no short in element it is just burnt wick.  Usually that means the fan is not spinning.  So a bad fan motor, which is driven off 5Vs.  G

If the PV going through the mux boards is bad, it should be obvious, that's a significant trace.  If it was blown, it would be pretty obvious by inspection. 

The PV diodes are on Engine MUX.  That is why motor lead power goes to it as input.  If lights work, the PV is not bad.  He is equating burned wick to some damage to a board.  Not the case.  Run smoke dry, it burns wick.  Have a fan failure, wick will burn. Loose impeller too.

Clearly something in engine though is running the 5V power supply near max output to cause the clicking and shutdown.  Smoke fan is #1 suspect.  But could be damaged wire harness too.  Hard to say, but I have seen some butcher jobs done on the mux and such.  Even on repairs where some one turns the tender into an upgrade tender but leaves the mux wiring in.  Lighting and smoke don't like that.  G

GGG you were right. It was the fan motors in both engines, not the mux boards. Thank you for the input! Learned something.

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