PS2 Reverse Problem

So "all systems worked well" initially.  Now the headlight goes out and moves at some minimum rate in reverse.  I'd say you have an intermittent wiring/harness short involving the wires to the headlight, reverse light, and/or the motor wires.

If inspection yields nothing, try removing the 12-pin 10-pin harness on the end of the large PS2 board that goes to the lights to see if the motor still runs itself in reverse.  Or remove the 5-pin motor connector to see if the headlight works in reverse.  This should only take a few seconds to try and might help isolate the problem.

Thanks stan2004 and GGG - I have to work this weekend and I don't want to rush this so I'll perform the diagnostics next week and report back.

Also, when Stan said remove 10pin he meant 12 pin.  This will disable the lights, but also sound.  I would check wires, then test with 5 pin removed (no motors).  See how the lights respond.  If normal, then reinstall the 5 pin and remove 12 pin and see what happens, just remember no sounds, lights or couplers.  Just smoke in DCS mode only.  G

I followed the suggested routines and found that:

Disconnecting the 12 pin allowed the motor to run in both directions but it was either on or off (no speed control).

Disconnecting the motor plug allowed the sounds, lights etc to work correctly but there was no "chuff" when I manually rotated the flywheel.

I connected another 3v PS 2 locomotive to the suspect tender unit and it worked perfectly.

I replaced the tach sensor and now everything now works as it should.

Under visual examination, the 'bad' tach sensor looks OK but I don't know how to test it. I don't know if I did something to cause the original tach sensor to fail or, if it just died after a few minutes use.

Thank you stan2004 and GGG for your help in this.

VERY odd that the tach worked in forward and not reverse.

Was it possibly angled relative to the centerline of the motor?

In any case THANK YOU for posting a follow up on the fix.

This is how we all learn to fix these engines.

That's really odd, it's hard to imagine why it failed, it's just the single sensor on the board.  Having it work in only one direction is even stranger.  I wonder if it's something really odd like some leakage in the photo-transistor that was more apparent depending on how the beam was reflected?

In the original post, the OP states the speed control sort-of worked in reverse in that he had speed control...but only above 10 sMPH or so.  I think the old tach board may be OK and there was a wiring issue...but it's moot at this point and this is just Monday morning quarterbacking...

I have seen other optical encoders only work in one direction, but never the PS/2 one.  I guess there's always a first time.

The exact way it was described is that it worked fine in fwd but when reverse was selected it moved off at 10 smph with out control input action on his part.

So I agree I am not sure how the tach sensor did this.  Tach sensors can fail, but it effects both directions equally.  Interesting one.  G

It sounds more like a wiring issue to me that was corrected when he opened it up to replace the tach reader. I just was driven crazy finding a short for a friends engine that caused the exact same behavior. PS-2 tach readers either work or they don't.

Could it be that the tack reader works, but it was skewed relative to the tack strip so that there was an intolerable bias affecting sensing the stripes in the reverse rotation? I think so.

Debris obscuring the tack reader also causes speed control issues.

I have seen optical encoders on other equipment fail in one direction only, so I know it's possible.

I have no idea if it happened here, or what the failure was.

I've had the same out of control situation in reverse happen before but in the 2 rail DC world. Ended up being the rail polarity was reversed from what PS2 wants.