Control for 1st generation Walthers Turntable (HO or N)

[nickelplate759]

 I obtained a used Walthers N scale Cornerstone 130' turntable,  (part number 933-2613, not the newer -2618 version) and I'm trying to put it to good use.   Walthers has no parts (of course), but does still have the instruction sheet.  I'm hoping that someone has experience with this board and can help me figure out how to get it working.

Since it's used, it needs a little  attention - the cosmetic stuff is easy, but I could use a little help with the control system.
Unfortunately, although I have the control board, it was partly disassembled at some point.  The original owner indicated that he didn't like the original pushbuttons, and replaced them with toggles. He even provided two toggle switches for me.

Here's a photo of the top side of the board:
[ Guests cannot view attachments ]
The four leads in the blue oval are described in the instructions - they're motor power and power to the bridge track.

The lead attachment points for direction switches are marked ("Plus" - orange oval - and "Minus" - green oval); there seem to be four wire attachment points for each switch.  The colors of the remaining attached leads at these points don't match the wires on the provided toggles (not shown) which are DPDT switches, wired as reversing switches. 

From reading the instruction sheet (which lacks circuit diagrams), it seems to me that the original switches were probably pushbuttons.  Although there seem to be four attachment points in each circle, the three points without wires do not have any traces on either side of the circuit board, so I'm not sure they do anything electrical.  I'd be delighted is someone could tell me how to correctly wire some switches up to this.

There's also an odd piece with two leads on it that may have been part of an original pushbutton (yellow oval).  I've no idea what to do with that.

After all that - does anyone know how polarity of the bridge track is handled?   For example, if I run onto the bridge, rotate the bridge 180 degrees, and then try and run back onto the same track I just came off of, will I get a short?  I'm using DCC, and don't really want to get a polarity reversing board just for the turntable bridge, but since that would be a problem in DC as well, I'm guessing it's handled by the turntable.

[reinhardtjh]

After all that - does anyone know how polarity of the bridge track is handled?   For example, if I run onto the bridge, rotate the bridge 180 degrees, and then try and run back onto the same track I just came off of, will I get a short?  I'm using DCC, and don't really want to get a polarity reversing board just for the turntable bridge, but since that would be a problem in DC as well, I'm guessing it's handled by the turntable.

The polarity of the bridge track is handled by a split ring setup were at a certain point in the spinning, there is a break in the contacts and the polarity reverses.  The turntable comes with an instruction sheet that explains it and shows where that break happens.  It governs how you place it in the hole so that the reversing happens at point where there are no lead or stall tracks.  I have one someplace. I"ll try to look for it and maybe scan it. 

Okay, turns out the instructions are online: 130' turntable - Walthers

The pertinent part is:

INSTALLING THE PIT
Your new turntable automatically reverses track polarity when turned. As a result, the unit has two electrically insulated areas where the track on the bridge is not pow- ered. These are identified on the underside of the lip by the “NO TRACK” lettering (also shown on the mounting template). Working approach and fan tracks must be installed away from these areas – we suggest placing them at 90° to the approach tracks. You can, how- ever, add an unpowered display track at these points if desired.

[peteski]

If you look at the sets of 4 solder pads circled green and orange, they are the same footprint as the push-button switches. Yes, those would have been push-buttons. Note that the the leads of the push-buttons are internally connected in pairs, and this circuit seems to have been exploiting that feature by using those 2 leads as a jumper (connecting the pad with white/orange and white wires.  For the circuit to work properly hose wires had to be connected together at the external switch lead.

Not sure what the device on the bottom of the photo is. Maye a closeup photo of the device itself would help.  Going by the color of the wires, it might have been connected to the 2 wires I descried above.  Maybe it is a a lead broken off of the external toggle that the previous owner installed?

[nickelplate759]

The "device" in the yellow oval is just a single piece of stamped metal with two wires attached soldered to it. 

So the rail polarity is indeed solved by the turntable - that's good.  I should have realized that from the instructions.

If the pushbuttons were dual pole, would they have been DPST (all four contacts made when pressed), or DPDT (two made when pressed, two when released)? 

[peteski]

The "device" in the yellow oval is just a single piece of stamped metal with two wires attached soldered to it. 

So the rail polarity is indeed solved by the turntable - that's good.  I should have realized that from the instructions.

If the pushbuttons were dual pole, would they have been DPST (all four contacts made when pressed), or DPDT (two made when pressed, two when released)?

The switches are simple SPST NO Momentary (like a doorbell switch).  It is just that they have 4 leads (for secure surface mounting).  Each pair of leads is connected internally (if you have an ohmmeter you can figure out which leads are connected inside the switch.   Like I said the internal interconnection between the switch's leads are actually used as a jumper (in the orange circle), permanently connecting the pads which now have the white and white/orange wires on them.  If needed, I can draw a diagram.
Maybe this helps?

| ___ |
|-o o-|
|     |


 
That metal thing is likely broken part of the external switch they used.  See if the cut wires match the wires still soldered to the circuit board - I suspect they will.

[nickelplate759]

The switches are simple SPST NO Momentary (like a doorbell switch).  It is just that they have 4 leads (for secure surface mounting).  Each pair of leads is connected internally (if you have an ohmmeter you can figure out which leads are connected inside the switch.   Like I said the internal interconnection between the switch's leads are actually used as a jumper (in the orange circle), permanently connecting the pads which now have the white and white/orange wires on them.  If needed, I can draw a diagram.
Maybe this helps?

| ___ |
|-o o-|
|     |


 
That metal thing is likely broken part of the external switch they used.  See if the cut wires match the wires still soldered to the circuit board - I suspect they will.

I don't have the original switches, just a pair of DPDT toggles that I'm not certain really belong to this turntable.

I think I've got it.  Looking at the connection points inside the orange oval - the connections that are  ALWAYS vertically aligned are connected inside the switch.  The connections that are horizontally aligned are connected when the switch is closed.

So, if the connection points are labeled as follows:
A - blue & white wire
B - white wire
C - no wire
D - Orange & white wire

  A   B
  C   D

Then A-C is is a closed circuit all the time, as is B-D,  but AC-BD is open unless the button is pressed.  Is that right?

[peteski]

I don't have the original switches, just a pair of DPDT toggles that I'm not certain really belong to this turntable.

I think I've got it.  Looking at the connection points inside the orange oval - the connections that are  ALWAYS vertically aligned are connected inside the switch.  The connections that are horizontally aligned are connected when the switch is closed.

So, if the connection points are labeled as follows:
A - blue & white wire
B - white wire
C - no wire
D - Orange & white wire

  A   B
  C   D

Then A-C is is a closed circuit all the time, as is B-D,  but AC-BD is open unless the button is pressed.  Is that right?

Almost there Gerorge!   

When button is not pressed, A-C are always connected and B-D are always connected.  When button is pressed than A-C get connected to B-D.
Like I said, the circuit board designed used the internal interconnection feature (specifically B-D) of the switch in the orange oval to jumper over the trace that runs under the switch.  The person who attached the external switches should have just soldered a short jumper between B and D, then ran a single wire (from either B or D) to one terminal of the switch, and another wire from A to the other terminal of his switch.

On the right side switch (green oval) only A and B are electrically active (and same goes for the remaining switches).

Hopefully this clears things up.

[nickelplate759]

Almost there Gerorge!   

When button is not pressed, A-C are always connected and B-D are always connected.  When button is pressed than A-C get connected to B-D.
Like I said, the circuit board designed used the internal interconnection feature (specifically B-D) of the switch in the orange oval to jumper over the trace that runs under the switch.  The person who attached the external switches should have just soldered a short jumper between B and D, then ran a single wire (from either B or D) to one terminal of the switch, and another wire from A to the other terminal of his switch.

On the right side switch (green oval) only A and B are electrically active (and same goes for the remaining switches).

Hopefully this clears things up.

I think it does.  I'll do some experiments this weekend and find out if it works the way I understand it.

[peteski]

I think it does.  I'll do some experiments this weekend and find out if it works the way I understand it.

Very good.
Actually, to fully clarify the electrical circuit, the B-D terminals are also  used as an electrical jumper, then on the other side of that switch they use A.

Then the Zero switch is rotated 90 degrees, so its terminals are:
C  A
D  B
On that switch only terminals B and C are used.

[nickelplate759]

Well, the board is alive and wired exactly as Pete said (imagine that....).  Now I need to get the mechanism healthy.  It's been stored for some time, and has a visible and audible hitch in the drive train and also some visible crud in the gear teeth - probably related!

[edit]   Decrudding the gears helped, but it runs far better clockwise than counterclockwise.  Some of the gears get out of alignment running counterclockwise.  There was/is a LOT of grease in the gear train, and I haven't figured out how to remove the motor to do a thorough cleaning, but I got a lot of the grease out anyway.   At least the electronics are working well.  While I'm at it, I'm wondering hard it would be to change out the code 80 rails for code 55 - has anyone tried that?[\edit]

[peteski]

@nickelplate759
George, can you post a photo of the other side of the controller board?

[nickelplate759]

Here's the back.  Not much on this side.

[ Guests cannot view attachments ]

Just a cap (220 micro farad, 35V)

and the 3-conductor gizmo (voltage regulator maybe?) which is labeled

TS7812
[some logo]
ACA CZ     (or maybe  4CA CZ - the first character is unclear).

[peteski]

Hmmm . . .
As you suspect, that 3-leg device (7812) is a 12V regulator.
What I don't see on either side of the PC board are any power transistors to drive the motor.  The microcontroller outputs should not be not robust enough to drive the motor directly. If the bridge can move in both directions I would expect a 4-transistor H-bridge. I wonder if those transistors are somewhere else? Like closer the motor (is there another PC board under the turntable or in the bridge)?

[rodsup9000]

 Yes, Pete there is

[nickelplate759]

Yes, there is a circuit board in the bridge too (as posted above - simultaneous posts); it looks more complex than the controller board, but it's also a lot smaller.  I'm guessing that's where most of the smarts are- it needs to count turns, stop when things are aligned correctly, etc.     There are eight 24 gauge conductors between the controller and the turntable.   I don't know if they are all used - it looks to be a standard Cat 5 cable, complete with  RJ45 connectors.     I can't tell if there is another board in the round box under the pit well without taking it apart, but the zero-point LED is in the pit and has a couple of wires running to it from that box.