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Has anybody used these instructions from Williams by Bachmann to add a lockout switch to their (early version) Williams e-unit board, and been successful?

I performed this mod, and in the “normal” or “unlocked” position, I got the expected F-N-R-N-F-etc. But in the locked position, the motor ran for less than one second, then just stopped. It would not do anything after that, even through cycling power on and off, until I changed the switch to the “Unlocked (or normal) position. Things worked normally again in unlocked, but when I changed the switch backed to “Locked”, it once again ran for a second, then shut off. This can be repeated any number of times, but it has never successfully locked the engine in one direction.

Looking at the instructions in line 1, they state: “Solder a wire from the junction of the 22K/10K resistors (see diagram) to one outside terminal.” The problem I’m seeing is that the only junction of those two resistors occurs on the left side of the resistors when looking at their diagram, not the right side as they have drawn. When I hook the wire to the left side, it pops my #91 breaker on my ZW. I have been unsuccessful trying to find a schematic for this board. I should add that my board appears to be identical to the board they show with the exception that mine does not have any sockets on the right hand side, just solder pads/holes.

I would appreciate hearing from someone who has successfully done this.

George

Last edited by GeoPeg
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Chuck and Stan - thanks for your replies. I wish I had seen the "Rev 4 only" note earlier. My board is R2, and although it is quite similar in appearance, there are some differences. It does not have the sockets (on the right end) as the one in your photo does. I also noticed that R1 is a different value, and the PWB foil patterns are different. So, thanks for the picture, that certainly helped to understand a very plausible reason why it's not working. I guess I'll just run it without a lockout for now.

I also noticed the relays are really wimpy! At 2a for AC and 1.25a for DC, I'm surprised the single MPC era Pullmor motor hasn't killed it yet! We'll see how long it lasts

George

@GeoPeg posted:

.... I guess I'll just run it without a lockout for now.



But are you still interested in a DIY lockout for version R2?

I'm sure we could concoct an inexpensive modification but it would take some sleuthing (reverse-engineering) to sketch out certain portions of the circuit.

Separately, does anyone know

1. why these E-units have two bridge rectifiers? 

2. are the two relays configured whereby one does polarity reversal (DPDT) for DC direction, and the other is performing dual-pole OFF-ON to disconnect the motor when in Neutral?

@stan2004 posted:

But are you still interested in a DIY lockout for version R2?

I'm sure we could concoct an inexpensive modification but it would take some sleuthing (reverse-engineering) to sketch out certain portions of the circuit.

Separately, does anyone know

1. why these E-units have two bridge rectifiers?

2. are the two relays configured whereby one does polarity reversal (DPDT) for DC direction, and the other is performing dual-pole OFF-ON to disconnect the motor when in Neutral?

Yes, I would still be interested in a Lockout. If someone has access to a schematic, that would be exceedingly helpful - even a Rev 4 schematic would make a great starting point!

George

So, OGR being a discussion forum, let's discuss!   The expedient "solution" is to just replace the Rev2 E-unit with one that has a plug-and-play lockout switch.  But where's the fun in that.   

So if we agree to the premise that the Rev2 E-unit stays, I see several alternatives to lockout.  I offer my ramblings, a.k.a. 2-cents worth:

Option 1. Add a DPDT switch and an external $1 bridge rectifier.  This requires no modification to the Rev2 board.  The external bridge rectifier converts track AC to DC just like the on-board bridge rectifier(s).  The DPDT switch selects between whether the DC-can-motor is driven by either (A) the Rev2 board with its reversing capacity, or (B) the DC bridge-rectifier output which locks the engine in a fixed direction.  The gotcha may be that the $1 DPDT switch must be able to handle the 1-2 Amps or whatever Amps current the engine requires.  Since your engine does not presently have reversing capability, I assume you'd need to cut a hole in the chassis to access the lockout switch so this could mean a slightly larger cut-out than a typical lockout switch (e.g., the type proposed by Wbb for their Rev4 board) which only carries a fraction of an Amp of current.

Option 2. Same as above but "steal" the DC voltage from the on-board bridge rectifier.  Still need a DPDT switch that can carry the DC motor current but saves the cost of the external bridge rectifier.  So this would require finding someplace on the PCB to solder 2 wires that represent the DC output of a bridge rectifier.

Option 3. Reverse-engineer how the 2 relays are driven to "force" them to be in the Forward position.

2 relay transistors

This is mere speculation, but my guess is the 4 states (F-NBR-R-NBF, NB=Neutral Before) of the E-unit map to the 4 possibilities of the 2 relays.  Each relay is driven by what is in effect an "on-off" transistor as circled in red.  If the lockout switch could force the 2 transistors to whichever on-off condition to make the relays drive the motor to the Fwd direction then we're done!  The currents involved with the transistors are minimal when compared to the Amps of current when dealing with the motor currents themselves.  So the lockout switch could be a smaller, less-expensive, double-pole switch.  The switch would either allow the transistors to be driven by (A) the existing circuit, or (B) by some circuit which "forces" the transistors to the desired on-off states.  This may require a few 10 cent diodes/resistors.  This would also involve some study of how the transistors and nearby components are interconnected which means sketching out the interconnections of the traces on the front and back of the PCB.

Option 4.  The available Rev4 WBB diagrams suggest the magic IC chip is the 4017.  This is an inexpensive 50 cent digital counter chip which counts 1,2,3,4,1,2,3,4,1,2,3,4, etc. to cycle thru the 4 possibilities of F,NBR,R,NBF, F,NBR,R,NBF, F,NBR,R,NBF, etc.  You might want to confirm that the Rev2 IC chip has the marking "4017".

4017

So in this option, the idea would be to force the 4017 counter IC to remain at a fixed count (whether it be 1,2,3, or 4)...whichever corresponds to the Forward motor state.  This also requires documenting the interconnections on the front and back of the PCB; there are certain pins of the 4017 which are more relevant so you wouldn't have to document everything.  But like option 3, the lockout switch would only be carrying low-current signals  (vs. high-current motor power).  Like option 3, this may require additional of a few 10-cent diodes or resistors.  So in this case the lockout switch would select between (A) letting the counter IC chip advance 1,2,3,4,1,2,3,4,etc. every time the track power vanishes-and-re-apprears (pressing the transformer Direction button), or (B) blocking the counter IC from "seeing" the track power interruptions.

----

Separately, I believe what you're seeing with the modified Rev2 PCB running in Forward for only 1 second and then stopping forever is simply the counter IC chip advancing from Forward to Neutral-Before-Reverse and then sticking in the NBR state forever.

Attachments

Images (2)
  • 2 relay transistors
  • 4017

And the winner is ... me! I finally got back to this small project and read Stan & John's follow up, and I was motivated to review the pinouts for this IC. I thought that pin 13 looked promising as it blocks the counter from doing its job when in a HI state (normal operation = LO state.) Since this chip (4017) operates at 8.0v on pin 16 (Vcc), I simply tied the switch between pins 13 and 16 - no go - whatever circuitry was pulling pin 13 LO wasn't able to be overcome - pin 16 dropped to 0.2v, so the chip did not operate at all. So I tried John's idea to use the master reset, since this board does start in forward. There was enough ooomph on pin 16 to hold the reset HI, and that did the trick!

So with the addition of just a switch, the problem is solved and my #8063 SD-9 is now running around in the middle of a consist that fills my 4x8 ft table and is surprisingly well balanced in its current position (pair of powered 2032s in the lead and SD-9 in the middle.)

Thanks guys, I appreciate your thoughts, and willingness to jump in

George

Last edited by GeoPeg

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