Funky short circuit

[Anonymous]

I just built a small HO layout using (gasp!) cab control. It has 4 blocks on the main route. Cab 1is a Tech II 2400. Cab 2 is an old MRC throttle pack model 3. Blocks are totally isolated and cab selected via DPDT/CO switches.

Everything works fine except on the 2nd block. If Cab 1 (tech II) is on and I change the direction switch, it shorts/overloads. This doesn't happen on any other block, nor does it happen using cab 2. It occurs even if the block is empty(nothing on the track)! Like I said though, the problem doesn't occur under cab 2 control or on any other block. I'm lost as what to check.

[Anonymous]

I would suggest that you check out the reversing switch on your Tech II 2400.

[Anonymous]

Um, did you break both rails or are you using 1 rail common? What you say can happen with 1 rail common systems on pulse packs. FRED

[dknelson]

Did you use insulated rail joiners or did you just cut the rail with a Dremel tool? Sometimes those cuts close up if there is not a piece of paper or styrene keeping them apart
Dave Nelson

[Anonymous]

I'm using insulated joiners in both rails. I've tested the entire track with a digital volt/ohm meter and there is no continuity between blocks. Polarity all lines up corect. I even changed the power packs from 1--2,2--1 and changed the block switch. No change. I'd suspect the tech II reverse switch if the problem occured on all blocks, but again, it only does this on a single block.

[Anonymous]

If you actually changed places of your two power packs, connecting the Tech II to the wires of your old MRC and vise versa, and you still have the same problem with the Tech II, then I would tend to believe that you have a problem with the second block. Don't forget that elecrical gizmos ( Tech II power pack) wear out just like regular machines---- sometimes all at once, and sometimes over time. I believe the Tech II is a solidstate device( you know-- transistors, capacitors, diodes et cetera all mounted on printed circuitboards) as opposed to your old MRC power pack which is just a bunch of wires connecting switches, reostats, transformers and the like. On occassion the electronics, as they age, become sometimes less sensitive, or possibly, in your case more sesnitive to the outside world( your layout). I would say that there something triggering your Tech II somewhere between where you connect the wires to the back it and the track of block #2. Using your VOM on the more sensitive scales your going have to test all the wires and track in block #2. You really don't care about the other blocks because there aren't any problems there. What your looking for is a small short circuit that wouldn't be detected by the old MRC power pack. It could be something as simple as a couple of wires rubbing together and exposing bare wire. Look real close-- what would be nothing to would be really, really big according to your Tech II. Look real close at the points of any turnouts on block #2. Does the power that you use to opperate your switch machines in block #2 come from the Tech II, the old MRC or from a dedicated power source. If it comes from the back of your Tech II, then your going to have to test those circuits out, also. I know it can be a bear, but your going to have to be meticulous(sp) in your investigation--- you may even have to use a magnifying glass--really! I hope I scared you too much.

[BR60103]

I'll second what Paul said about checking turnouts -- if you have wire connections from the switch machine to a metal throw bar, you can get shorts. It could even be a short coming through the wiring from another switch machine.
Also check you DPDT switches for the blocks -- are any of the connections on them touching another switch?