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Old 12-30-2017, 10:28 PM   #1
GaryM
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Join Date: Sep 2016
Location: Washington
Posts: 2
Two decoders fried in the last week

The first was in a Tenshodo brass GN R2 2-8-8-2 to which a Tsunami decoder had been added by a previous owner (I bought it off eBay). There is no model # on the decoder, but it looks like a TSU-1100, though it may be an earlier version. The second was in a brand new BLI GN S2 4-8-4 with Paragon 3 sound.

This is a new layout, and I've been debugging track glitches for the past couple of weeks, making sure all locos would run the whole layout. It is a DCC HO layout using a Digitrax Evolution (DCS 210 booster/command station and a DCS500 throttle).

Here's the history:

R2: Tested the R2 first. It ran the layout fine with no derailments, except it would not negotiate a couple of 22" curves, which did not surprise me (all other curves on the layout are 30" or 36"). I ran it for a couple of days, avoiding the tight curves. It ran fine, all DCC functions worked. I set that loco aside, off the track, and tested the others. The S2 would not negotiate those curves either, so I re-laid that section of track to gain 2 more inches of radius --- all the room would allow. That solved the problem for the S2. Then I put the R2 back on the track to see if it would handle the wider radius. It immediately tripped the breaker in the DCS210. It had been off the track, undisturbed, for several days. Made sure all wheels on the loco and tender were on the track. Kept tripping the breaker. With this loco track power is picked up by the loco drivers on one side, tender wheels on the other side. The tender feeds to the decoder in the loco via the coupling strap. Separated the loco from the tender. That solved the short, but of course it would not run since the decoder was getting no power from the tender pickup. Pulled the shell off the loco, looked for frayed wires, etc. All looked OK. So removed the decoder from the loco entirely, snipping all wires. Connected track power to the red and black leads on the now-bare decoder. It tripped the breaker. Removed the 220uf capacitor connected to the decoder, thinking the cap might be bad. Still tripped the breaker. So the short is in the decoder itself.

S2: The S2 was also derailing on one of the turnouts. I discovered it would track it fine if not pulling a train. Apparently the load caused the loco to enter the turnout at a slightly different angle, and a wheel would catch on the guard rail. Ran it around the layout a couple of times with no train, then killed track power and added a few cars to the loco --- about half as many as before, to see if it still failed on that turnout. Turned track power back on and the breaker immediately tripped. Checked the loco and all the cars for proper tracking. Still the breaker tripped. So then removed all the cars, leaving only the S2 and its tender on the track. It kept tripping the breaker. It had been powered down for maybe 5 minutes. In this loco all the electronics are in the tender. A connecting cable feeds power from the decoder to the loco motor, headlight, and smoke heater. Disconnected that cable and removed the loco from the track, leaving only the tender. It tripped the breaker. Then I put the tender on the bench, removed both trucks, and connected the axle wipers to the track with jumper cables. The trucks were no longer connected to the tender body, the only connection was the two wires from the trucks to the decoder. Still tripped the breaker. So it looks like this decoder has an internal short also.

I also have a Walthers F7 A&B pair which are running fine. But now I'm afraid to run them, lest they also suddenly develop internal shorts. I did use my multimeter to see if the command station/booster was somehow sending some sort of power surge through the tracks when cycling track power on and off. Nothing registered; AC track power is a steady 13.75V. But I'm not sure that meter would show a spike if it lasted for only a few milliseconds.

Does anyone have any suggestions as to why this is happening? Locos run fine for a few days, then suddenly develop shorts for no apparent reason? Are there any combinations of CV settings that could short out a decoder? Replacing decoders every couple weeks could get expensive!

Any suggestions would be appreciated!
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Old 12-31-2017, 12:41 AM   #2
mesenteria
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Sorry, I haven't much to offer, except that a spike in voltage should do little if any damage to the decoder. I ran my HO layout for at least a full week with my DB150 accidentally flipped up to the O voltage position on the power setting toggle. I never did have a problem with the two or three locos I ran that week...or however long it was before I caught the mistake.

Now, if we were talking about wattage or amperage, then we'd have a distinct worry. Decoders let out their magic smoke when they get too much amperage throughput, such as during a short.

Have you done a 'quarter test', or used some other metallic object across the rails in several places to ensure the base unit's short detection can differentiate a short with the signal strength and voltage available?

I can't offer much about the BLI, except to call them and ask a tech to spend five minutes with you trying to figure out what could be wrong. If it goes badly, they'll give you a return authorization and you'll have it back inside of about 10 weeks...ish.

Metallic shelled and brass steamers have problems with metal parts coming into contact with other metal parts. The trucks can make contact with the frame or bits soldered onto the body serving as details as an example.

Do you have a dedicated programming track and circuit? You could test each decoder using clips to the rails to see if they are hooped. Digitrax used to include a decoder testing apparatus with their Super Empire and other packages.
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Old 12-31-2017, 12:51 PM   #3
DonR
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Join Date: Oct 2012
Location: Jacksonville, Fl
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Other than possible stray metal shorting on the
loco as suggested by Mesenteria, most decoder
burnouts are caused by excessive motor draw.

Most decoders today are rated to pass 1.5 amps.
Some older decoders were limited to 1 amp.
However, some older motors can draw more than
that.

Try a stall test on the motors of the damaged locos.

Put the loco sans decoder but with motor
connected on a spare track. Connect a
DC power pack in series with a multimeter set for
amps. Hold the loco from moving as you increase
the speed to about 3/4 or so. The wheels should
spin. Note the amp reading.
Then slowly press down on the loco until the motor
is stalled. Note the reading. If at any time that
reading exceeded the amp rating of your decoder
you have found the problem. That motor should
be replaced.

A loco that is pulling a train would draw more than without.
A loco running fast will draw more than one running
slow.

Don
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