Ps2 3v steam engine runs away

Yes the ps 2 3 volt boards can be repaired!

have you tried a conventional reset with z 4000 transformer? might make a difference there are also some chips on the board that can cause this issue or tack tape is it it in good shape! not coming loose on flywheel!good stripes and not faded!

sent you an email!

Chances are this is heat related and may not be repairable.  The typical board failure is the Power Supply for speed control.  Are you sure harness and the PCB at engine are good.  Solder joints can fail at engine connector (PCB).

But, you can swap another PS-2 3V PS on the processor and see if the problem goes away.  If not, processor board has issues.  Rare, but I have seen it.  IF the harness and wiring not the issue.  G

I have one processor board with a speed control fault in my junk box.  If it's the power supply, that's good news, it's more easily repaired.

NYCBuffalo posted:

...If i stop ( with dir button or drop track voktage) and start up again it will again usually run for a shorter period then drop chuff and take off again. I put in a new tach, no joy. Can the ps2 board be fixed or is it hopeless?

I take it you're interested in a DIY repair vs. sending it in.  I like G's idea that this might be heat related - and to try swapping in a different PS2 3V power supply board (the smaller board of the pair).   If you don't have a spare, or impractical/uneconomical to "borrow" a board from a fellow DCS operator (this would be a true test of a good friend ), you might try this simple experiment.

There is a $1 IC chip (circled in yellow) that processes the tach signal from the sensor.  It has been known to fail.  It can be a heat related phenomenon.  Let's say you can repeat the failure with the shell off.  When the failure occurs (chuffing sounds vanish and engine suddenly accelerates), lower the track voltage - something under, say, 10V - or wherever the engine is moving a some slow speed.  Then take a can of component-cooler spray (the red tube in photo) and spray as shown.  Ideally you'd want to cool just the chip itself but when the board-pair is installed you really can't access the chip with the side-mounting brackets.  So I show the spray hitting the other side of the circuit board to the IC chip.  Again, not ideal by any means...but if all of a sudden the chuffing returns and the engine decelerates as if under speed control, then I'd say it's enough to justify replacing the IC chip which can be quite a soldering hassle.  If you don't have component-cooler spray, even a can of compressed air should have enough cooling effect to lower the chip temperature.

Update: swapped the power board from a good engine, problem remains. Going to try the proc board to see if that is it.

Well not the proc board. Put whole board set from good loco in the trouble engine and it still eventually ran away. Put boards from bad loco in good engine and its fine. Maybe my new tach is bad?

Its odd it runs so long before dying. Like as it runs the chuffs get less and less till there is just one random chuff sporadically.

You didn't mention what model this is.  If the boards are in the tender, you need to take a close look at the tether.  I think it's time to use an ohmmeter and meter out the leads from the tach sensor to the board.  The tach reader goes to the 7-pin connector on the board, you should have continuity from all three pins.  Pins 1, 2, and 3, connect to the tach reader.  If they all don't have continuity to the tach reader, you'll get a runaway.  Top three pins go to the tach reader.

Obviously, the tach sensor could be bad, I've put a bad replacement in a couple of times.  However, if my replacement doesn't work, then I get my 'scope out and see if it's really generating a signal before replacing again.

NYCBuffalo posted:

Well not the proc board. Put whole board set from good loco in the trouble engine and it still eventually ran away. Put boards from bad loco in good engine and its fine. Maybe my new tach is bad?

Its odd it runs so long before dying. Like as it runs the chuffs get less and less till there is just one random chuff sporadically.

If the chuffing and speed control come back after letting the engine cool down, it still sounds heat related.  

If you can run the engine with the shell(s) off, I'd run it till the chuffing disappears and lower the voltage so it's not zipping around the track.  Then use a popsicle stick or the like at poke at all the connections from the tach board thru any harnesses etc. back to the power supply board.  Then, if you have component-cooler or even compressed air dust-off, spray the windowed sensor chip on the tach board.  Or blow hard thru a soda straw at the chip!

the tach reader board is very cheap so why not get one or take the tach board out of a another  good engine that works and try that then you'll be sure if it works you'll know exactly what the problem was! I doubt it is a bad connection on the tack board but this will prove what your problem is if it works after substituting   a know good tack board from another engine! 

Well, before ripping engines apart, I'd just make SURE the connections are secure.

I said that in the beginning to check wiring, though it would be weird for wiring to be fine for 30 mins.  Since this is PS-2 3V steam, is it a premier engine or a RK with more features.  It could be a mux set up where the 5V comes from the MUX board in the engine for the tach reader.

But at this point, I am with alan to replace the tach reader.  After that you will need to look at the mux board.  Does the lighting function stay on in the engine when it looses speed control? G

gunrunnerjohn posted:

You didn't mention what model this is.  If the boards are in the tender, you need to take a close look at the tether.  I think it's time to use an ohmmeter and meter out the leads from the tach sensor to the board.  The tach reader goes to the 7-pin connector on the board, you should have continuity from all three pins.  Pins 1, 2, and 3, connect to the tach reader.  If they all don't have continuity to the tach reader, you'll get a runaway.  Top three pins go to the tach reader.

Obviously, the tach sensor could be bad, I've put a bad replacement in a couple of times.  However, if my replacement doesn't work, then I get my 'scope out and see if it's really generating a signal before replacing again.

my first one gauge challenger did something like this. As it got worse I finally realized that it was the tether. All it needed was to have the solder joints re-melted. It has been fine ever since.

I believe what happened for me was just the sound was cutting out. That's because in one gauge, the board set is in the boiler.

Are the tach wires sent thru the tether in this model?  would that even cause a runaway?

GGG posted:

I said that in the beginning to check wiring, though it would be weird for wiring to be fine for 30 mins.  Since this is PS-2 3V steam, is it a premier engine or a RK with more features.  It could be a mux set up where the 5V comes from the MUX board in the engine for the tach reader.

But at this point, I am with alan to replace the tach reader.  After that you will need to look at the mux board.  Does the lighting function stay on in the engine when it looses speed control? G

However, since he's already replaced it, I'd say look for other causes before replacing it again.

From the original post to start the thread.

NYCBuffalo posted:

I put in a new tach, no joy. Can the ps2 board be fixed or is it hopeless?

Sure.  But I have had bad tach readers. They are sensitive.  Still have not seen a wire issue that ran for 30 mins fine.  Cracked solder joint will open when stress of harness moves it in a curve.  Same with tether break.  But hey, never say never.  G

NYCBUFFALO, before I had stationary rollers to run an engine in place, I would shim under the front pilot and cab with playing cards or business cards just enough to raise the drive wheels off the tracks about a 1/16". Once you have the perfect height, put a rubber band around the stacks of cards. That way you can run the engine at a slow speed, and move the tether around to test it, without it taking off around the layout. You will need a ground wire with alligator clips to ground the chassis if the engine has no front pilot or cab wheels for ground. The pickup rollers will still make contact with the center rail if you don't go too high.

I had a failure about two years ago with exactly the same symptoms.  It was (as Gunrunner John has suggested) a bad tether.  The engine has been fine since.

RAK posted:

I had a failure about two years ago with exactly the same symptoms.  It was (as Gunrunner John has suggested) a bad tether.  The engine has been fine since.

 

Run for up to 30mins and then by stopping engine it will work fine again?  Got to admit I have never run across it, but anything is possible I guess.  For the PS-2 3V changing tether is easy enough normally.  It typically is the first thing I do, followed by engine PCB reflowing of solder.  G

Usually, if it's a bad tether I can put it on the rollers and wiggle the plug around and force the failure.  As far as heat build-up, I keep a can of freeze spray and my small nozzle heat wand handy to heat and cool parts for troubleshooting.  Also, don't discount a very close physical inspection, more than once I've found a surface mount part with a bad solder joint that just needed to be touched up.  I find this tool valuable for inspecting small components, I can zoom in and have a tiny chip resistor fill the screen.  It also allows you to record pictures and video to a micro-SD card.

600X 4.3" LCD 3.6MP Electronic Digital Video Microscope

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