I'm basically an N scaler, but I've picked up a few HO and O pieces in my favorite road lately. I broke down and bought the Kato Unitrack WGH plan set to run my HO on. I didn't build the whole layout yet, I just threw together an oval with sidings at each end. I hooked it up to a Kato DC power pack and everything ran fine, including my one DCC equipped HO loco. Then I switched all the turnouts to non-power routing and connected my Digitrax Zephyr. My one DCC loco, an Atlas GP40, runs fine until it hits one spot on the rails. Sometimes it passes this spot with no problem, and sometimes it hesitates, the lights go off, and the Zephyr's display goes into short-circuit mode for half a second or so. It doesn't happen every time around the track, but it always happens in the same spot. I cleaned the (new) track, changed out the track pieces, and even insulated one end of the problem track piece in case there was some kind of ground loop or standing wave issue. None of these had any affect. I switched the turnouts back to power-routing and put the DC power pack back on. The GP20 passes that spot with no problem again. I have never seen anything remotely like this happen with my N scale Unitrack, but it doesn't have turnouts that you can configure for non-power routing. I'll be grateful for any and all input.
Interesting. Can anyone explain how out of gauge wheels would cause a short in DCC and not in DC operation? I was thinking it had something to do with non-power routing on the turnouts, even though the track in question is two sections beyond the non-diverging branch of a turnout. Because its always at the same spot in the track, I suspected the track might be out of gauge, or have some other problem; but replacing that piece of track made no difference.
Are you pulling any rolling stock at the time this happens? If so it could be a piece of your rolling stock causing grief at the turnout and not the loco at all. If it happens nowhere else and you have replaced that section of track it would seem the problem is elsewhere.
Lownen, have you tried running the loco using the Zephyr with the turnouts set for power routing and get the same result? Ben
Ben; Haven't tried that yet, thanks for reminding me. Thought of it last night. Why do people get all their best ideas when you're lying in bed trying to fall asleep? I also need to pull off the rolling stock like jdvass said. I started out testing in DC and switched to the Zephyr when I had the cars already connected.
Bingo! The problem remained even when the switches were set to power routing under DCC. The pause occurred just after a caboose with metal wheels passed through the closed turnout. Why it didn't happen when the turnout was thrown, and why it didn't happen on other turnouts, why it only happened under DCC, and what the metal wheels were actually shorting remains a mystery to me. But at least I found the gremlin.
DCC is more sensitive to shorts than DC (generally). Eg. what you can get is a wide wheel tread that spans across the gap between the two rails at the frog and momentarily shorts them together. On DC this will typically cause a spark and maybe a moment's hestitation, but inertia, and some electrical brute force, moves the problem by and you may not even notice it happening. On DCC the electronics detect the short very quickly and kill the power. It is restored very soon after, but in the meantime the decoder has shutdown and takes a while to 'reboot'. It is very noticable with sound locos As you have a reproducible event now you should be able to look closely at things and identify the cause. Don't assume it really is that caboose/wheel/location on the turnout - the real culprit might be a few inches away on the other side.
Removing the caboose resolved the problem, I ran it for five minutes with no decoder "reboots" before replying. Prior to that the decoder rebooted at least 50% of the time when it crossed that section of track. Your explanation of the wide wheel tread sounds exactly like the what was going on, and the caboose wheels seem to have been the guilty party.
There are 8 million stories in the city. This has been one of them. Read my last post on the Kato GS-4 thread (N Scale forum) for another. Ben
Lownen, If this was never resolved, you might want to look be sure that your turnouts are well supported. I had O scale turnouts that shorted when too muchweight went across them and they actually threw the switch. Once I supported the base properly, it didn't happen. I was thinking if your turnout flexed at all, plastic wheels wouldn't matter, but metal might.
Thanks Marty. This was resolved, it was indeed out-of-gauge wheels on the caboose. HO isn't my primary scale, and I didn't have an HO gauge at the time. Best!
