Repair a diode matrix for twin coil switch machines

[EdGDent]

(Please note I have no experience with electronics)

Built a diode matrix (MR article) years ago for twin coil switch machines.A ladder with 5 switch machines leading to 6 tracks using heavy duty silicon diodes.The machines are powered by a capacitor (snap action control).  Machines are thrown by a six position rotary control with one push button.

The matrix worked fine for many years.  I have had a hiatus from the hobby and upon return find that the machines after the first two in line are not switching although they emit a sound as if trying to work.  The last turnout motor (#5) does throw with positions 5 or 6 on the rotary control (using one push button for power).

 Is there a way to test the diodes?  I hate the thought of rebuilding and would appreciate any suggestions.

Thank you.

[rrinker]

 Yes, a halfway decent multimeter has a diode test option. You would at least have to disconnect the matrix to prevent sneak paths when testing, but otherwise should be able to put the leads across a given diode and check it.

 Alternately, the diodes needed are pretty cheap these days, might be worthwhile to just build it new if you suspect the diodes have failed. Since the behavior is pretty much the same for all of them, I'd think about what is in common to all routes - it's not likely that ALL of the diodes would have failed at one time. The CD power supply, yes, or the rotarty switch might just have dirty contacts. Check the big capacitor - electrolytic capacitors fail with age, if it's bulged or oozing any material, that's your problem. You can test the CD supply by hooking it to one switch motor (bypass the matrix and rotary switch) and see if it snaps the machine over like it should (don't touch the bare wires when doing it, you WILL get a jolt). If that works fine, then it is either the switch or the diodes, and I'd still suspect the switch before the entire matrix of diodes, especially if it has been in storage for a significant amount of time. Or just worn contacts from age - a rotary switch isn;t really meant to handle the current of a CD machine operating twin coil motors. It 'works' because it's a quick pulse and because you aren;t switching the contacts under those sort of loads (or at least shouldn't be - that would be holding down the pushbutton and then turning the rotary switch, kind of backwards). Eventually though, the exceeding the ratings will catch up with you.

                      --Randy

                      --Randy

[DigitalGriffin]

You said like "they sound like they are trying to work."  Have you hooked the switch up directly bypassing the diode to see if it works?  It is possible the switch is jammed or the throw linkage disconnected.

 

[Tony73]

As stated above, I would check contacts/ connections first. One other thing, I had a similar issue with one of mine in a staging yard. One of the tracks was rarely used. The issue with not throwing, making noise came up.. It seems somehow a small piece of something (plastic?) got tn the way and was not allowing the turnout to throw properly.. so check that the turnouts are not binding due to foreign objects or friction with roadbed.

[richg1998]

All my years of working with diodes, they either open or short. An ohm meter will show you that very quickly.

I would suspect the turnout is hanging up or a rotary switch contact is the culprit.

Right now, assuming the OP does not have a meter.

The below cost maybe a couple dollars and cheap to replace if damaged.

http://www.trainelectronics.com/Meter_Workshop/index.htm

One more thing I just thought of, a connection can look ok with an ohm meter but a sudden surge of current can cause the connection to interupt the flow of current. Has happend to me a couple of times over the years.

Rich