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12 replies

Erratic Switching on multiple ATLAS 6924 boards

J JVM-51OGR Forum Member

Problem Background: About a year ago I posted about a problem with an Atlas O 3-rail turnout. It was switching back and forth without any input from the controller or the insulated control rails. The turnout and the switch machine were connected to an Atlas 6924 non-derail board. The 6924 provided non-derail and power routing. The problem was (I believe) caused by bundled wires between the 6924 and the switch machine, the insulated control rails and powered closure rail(s). Once power was routed to the closure rails, the erratic switching behavior would begin. The problem was resolved by physically separating the closure rail power wires from the low voltage control rails and switch machine wires. I now have 20 switches operating in this configuration with power wires for the closure rails isolated from other wires going to the turnout.

New (related?) Problem: I have added a panel to control block power (25), turnouts (20), and uncoupling (not connected yet). The block control has enabled me to shut off engines that are not in active use. However, when none of the engines are in any active power block, all 20 turnouts begin switching randomly!! If I apply power to a block with an engine in it, the random switching behavior stops.

Prior to adding the control panel there were no controllable blocks on the layout. All track was powered and there probably was always at least one engine on the layout so I don’t know if this issue existed before adding the panel. It seems strange that every 6924 board spread around that layout is immediately affected when no engines are powered but power is available to vacant blocks elsewhere on the layout.

I suppose it may be important to note that switch control wires and track power wires are all routed through the panel. I am using DPDT toggle switches for block control and SPDT momentary toggle switches to control the turnouts. Block switches and turnout switches are in close proximity on the control panel. The layout is powered by a single ZW-C controlled by a Legacy base.

Of course I would appreciate your help in resolving this issue

Joe

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Mike CTMike CTOGR Forum Member

Check with Atlas, I think there is a fix, done by adding diodes to the two isolated rail inputs.  The boards appear to be sensitive enough to pick chatter from the rails, enough to trip the boards.  Of my 20 some boards I only have two that exibit this, and only in conventional use, of the TMCC or DCS system.  If you get no response from Atlas, contact Steve Horvath, forum member.   Underlined phrase should link Steve's forum profile.

Last edited by Mike CT
rrmanrrmanOGR Forum Member

My two cents from EE and quality control perspective: not enough engineering thought or testing went into what otherwise is a good design idea.  Sounds like sensitive analog parts, insufficient bypassing, not separating grounds to one point, or who knows.  Maybe used minimum parts to get working to get price point?   Reminiscent of Muntz TVs (if you don't know what I am talking about, contact me off line).

OmanOmanOGR Forum Member SUPPORTING MEMBERDIGITAL SUBSCRIBER
JVM-51 posted:

Thanks RRMAN and Keith.  I have contacted Atlas and am waiting to hear back.  Keith, I don't know how or if I can bypass the FWR on the board or if I could damage the board doing it.  I will also ask Atlas about DC direct to the board.

Joe

Well, I was way off on that reply. The board has a 5 volt regulator and a Microchip microcontroller. I thought it was just a bunch of relays. It still may perform better on pure DC. You do not need to bypass anything on the board, just apply pure DC instead of AC.

Last edited by Oman
rrmanrrmanOGR Forum Member

Guessing that the microcontroller inputs are not sufficiently bypasses or conditioned and respond to noise or surges that interpreted as valid.  Usually can be fixed in software by delay loops so input has to be held on or off sufficiently long time, relative to noise impulses, before considered valid.

OmanOmanOGR Forum Member SUPPORTING MEMBERDIGITAL SUBSCRIBER
rrman posted:

My two cents from EE and quality control perspective: not enough engineering thought or testing went into what otherwise is a good design idea.  Sounds like sensitive analog parts, insufficient bypassing, not separating grounds to one point, or who knows.  Maybe used minimum parts to get working to get price point?   Reminiscent of Muntz TVs (if you don't know what I am talking about, contact me off line).

It seems like a Rube Goldberg design. It takes 3 relays and a microcontroller to accomplish this function? 

J JVM-51OGR Forum Member

Actually, the boards seem amazingly functional when not affected by spurious signal that triggers this odd switching acation.

Non-derail, power routing for two power sources, panel / trackside signals, switch machine burnout protection and maybe more that I have not figured out.

I'm don't know if this condition is unique to me, caused by something I've done with my wiring or if others are experiencing this as well.  

 

OmanOmanOGR Forum Member SUPPORTING MEMBERDIGITAL SUBSCRIBER
JVM-51 posted:

Actually, the boards seem amazingly functional when not affected by spurious signal that triggers this odd switching acation.

Non-derail, power routing for two power sources, panel / trackside signals, switch machine burnout protection and maybe more that I have not figured out.

I'm don't know if this condition is unique to me, caused by something I've done with my wiring or if others are experiencing this as well.  

 

I have a "test suggestion". If you can completely isolate the board power from the switch machine power, try powering all of the non-derail boards from a 12 VDC battery. I suspect that electrical noise is coming in the input terminals and coupling across to (what should be an isolated circuit) the internal 5 volt circuit. If the power for the internal 5 volt circuit is derived from a battery, you will break the signal path and the problem should cease. If my thinking is correct, a powered locomotive shunts this electrical noise to common or ground.

If you have wired the same power source to both the inputs and the board power terminals, this may be easier said then done.

OmanOmanOGR Forum Member SUPPORTING MEMBERDIGITAL SUBSCRIBER
JVM-51 posted:

Here is the wiring diagram.  the board gets internal power from the ZW B terminal.  The Power routing and track power is coming (currently) only the ZW D terminal. All circuit go to the common ZW U terminal. 

 

 

Nice diagram. I am suggesting to disconnect terminals 16 & 17 from the ZW. Then connect terminals 16 & 17 to a 12 volt battery. This, of course, is for testing only. If the problem goes away, I can suggest solutions.

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Tags: ATLAS, Erratic Switching
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