Trouble-shooting a balky loco/turnout combination

[reinhardtjh]

Taking it even further -- do you know of any good, small digital oscilloscope, that could be used to view the DCC waveform?  (Something simple - I don't think I will ever need to look at a PCI bus.)

(I was thinking even maybe a DIY kit would be fun.  And not the beast that I had in my school lab - an HP vacuum tube job that weighed about 100 lbs and was older than some electrons)

Ed

I own the good old trusty Tektronix 465B analog scope, and several years ago I bought a small Rigol Digital Storage Scope/logic analyzer. I also own an old palm-size portable analog scope. I have not kept up to date on the current oscilloscope market.  But I know that you buy a small adapters which turn your smart phone into an oscilloscope. I'm sure there are different versions with various capabilities (and prices).

A quick Duck Duck Go search came up with this: https://www.amazon.com/Oscilloscope-OSC482M-Channels-Bandwidth-Resolution/dp/B07TB8V2X1/ref=sr_1_1_sspa

Like Peteski I have an "old" Tek scope - 2445A 150Mhz that I got on Ebay a few years ago.  Was a couple hundred at at the time.  Since moving to Texas and my work area has downsized a bit I just ordered a Rigol digital storage scope. Probably a similar model to Peteski's - DS1104Z Plus.  It's a 100MHz 4-channel with a 16-channel logic analyzer.  It's much smaller (and thinner) than the Tek and will fit easier around here.  I bought it primarily to work on my vintage computers - a DEC PDP-11 and similar systems.  No PCI bus but there's a QBus and UNIBus (DEC Propitiatory). But it will also come in handy eventually checking DCC waveforms and working on various Arduino and other hardware projects.  It's got good reviews plus a former DEC engineer now with Intel has one so that's worth a little bit (this subject oscilloscopes - just came up on the PiDP-11 Google list).


It's probably overkill for what you want, but here's the link.  https://www.amazon.com/gp/product/B016QK05H0
Peteski's link might be more what you want for poking around the railroad.

The logic analyzer probes are extra - https://www.amazon.com/dp/B071LN38B9

[davefoxx]

A multimeter is nice, but an ordinary 12-volt light bulb, the once-common grain-of-wheat type, will work just as well for dead track.  Turn the power on, and touch the leads to the various rails.

It won't help you find a short, but for stalling locos it works fine.

I’m cracking up at how this thread turned to a debate on multimeters.  Those posters are not wrong as to the uses of a multimeter by model railroaders, but as @nkalanaga pointed out, for this purpose, all you really need is a 12v bulb and two leads.  I have a multimeter, but I find the simplicity of this bulb, again, for this purpose, to be ideal.  Light on: power!  Light off: no power!

I’ve had this gem for probably thirty years. It’s my goto tool long before I drag out the multimeter.  And, it requires no batteries! 



DFF

[MK]

Sometimes we  can't see the tree from the forest.   

On that note, I think I'm going to run down to the basement this afternoon and make one with a LED, a resistor and two mini alligator clips.    Then throw it in my traveling tool box (for train shows).

Edit: and a bridge rectifier for DCC layouts.

[peteski]

Sometimes we  can't see the tree from the forest.   

On that note, I think I'm going to run down to the basement this afternoon and make one with a LED, a resistor and two mini alligator clips.    Then throw it in my traveling tool box (for train shows).

Edit: and a bridge rectifier for DCC layouts.

Do one better:  Use a red/green LED with only 2 leads (internal LEDs wired in reverse parallel) and a resistor.  That one will not only show the track polarity, it will also glow yellow for DCC signal (since the polarity reverses so  fast, the red and green colors blend into yellow).  No rectifier needed as each LED will protect the other from excessive reverse voltage.  Or just use 2 discrete LEDs (red and green) wired that way.

No, I did not come up with that idea, but I think it is a good one.

[nkalanaga]

Peteski:  Yes, that IS a good idea, especially when dealing with layouts that can run both DC and DCC.  Even in straight DC layouts, with multiple blocks, it's possible to reverse the feeders for a block, which will give a very frustrating stall.  Both blocks have power, but the train shorts out!  My light bulb wouldn't detect that problem, at least just by checking the individual blocks.

[Maletrain]

Peteski:  Yes, that IS a good idea, especially when dealing with layouts that can run both DC and DCC.  Even in straight DC layouts, with multiple blocks, it's possible to reverse the feeders for a block, which will give a very frustrating stall.  Both blocks have power, but the train shorts out!  My light bulb wouldn't detect that problem, at least just by checking the individual blocks.

But it would show the problem if you put it across the rail gap between blocks.  I check both rails, just to be sure that it is really reversed on both.

And, it you want to go a step further, putting a 9 volt battery in the circuit with the bulb can show shorts (on an unpowered layout, please).

[davefoxx]

Do one better:  Use a red/green LED with only 2 leads (internal LEDs wired in reverse parallel) and a resistor.  That one will not only show the track polarity, it will also glow yellow for DCC signal (since the polarity reverses so  fast, the red and green colors blend into yellow).  No rectifier needed as each LED will protect the other from excessive reverse voltage.  Or just use 2 discrete LEDs (red and green) wired that way.

No, I did not come up with that idea, but I think it is a good one.

Sadly, not for us colorblind guys.

DFF

[davefoxx]

But it would show the problem if you put it across the rail gap between blocks.  I check both rails, just to be sure that it is really reversed on both.

Agreed.  I can also verify the polarity changes of frog juicers and automatic reversing sections.

DFF

[MK]

Do one better:  Use a red/green LED with only 2 leads (internal LEDs wired in reverse parallel) and a resistor.  That one will not only show the track polarity, it will also glow yellow for DCC signal (since the polarity reverses so  fast, the red and green colors blend into yellow).  No rectifier needed as each LED will protect the other from excessive reverse voltage.  Or just use 2 discrete LEDs (red and green) wired that way.

No, I did not come up with that idea, but I think it is a good one.

Peteski, can you draw schematics for both construct, one with bi-color LED and the other with discrete LEDs?  Thanks.

[CRL]

I%u2019m cracking up at how this thread turned to a debate on multimeters.  Those posters are not wrong as to the uses of a multimeter by model railroaders, but as @nkalanaga pointed out, for this purpose, all you really need is a 12v bulb and two leads.  I have a multimeter, but I find the simplicity of this bulb, again, for this purpose, to be ideal.  Light on: power!  Light off: no power!

I%u2019ve had this gem for probably thirty years. It%u2019s my goto tool long before I drag out the multimeter.  And, it requires no batteries! 



DFF

And notice how quickly your simple 12v bulb method to determine power or no power started getting complicated immediately by going to an LED, then 2 LEDs, then red/green LEDs morphing to yellow and so on into the void!

[MK]

We can make anything better!  It's the TRW way!   

[nkalanaga]

Maletrain:  That's how I found it, years ago. 

DFF:  The "2 discrete LED" version would work for the colorblind, as long as the two are labeled.  Put them side-by-side in some type of holder, and write the color next to each one.  It would work the same for those of us who can see color, and those who can't can read the labels, so everyone can use it.

[MK]

Do one better:  Use a red/green LED with only 2 leads (internal LEDs wired in reverse parallel) and a resistor.  That one will not only show the track polarity, it will also glow yellow for DCC signal (since the polarity reverses so  fast, the red and green colors blend into yellow).  No rectifier needed as each LED will protect the other from excessive reverse voltage.  Or just use 2 discrete LEDs (red and green) wired that way.

No, I did not come up with that idea, but I think it is a good one.

Peteski, can you draw schematics for both construct, one with bi-color LED and the other with discrete LEDs?  Thanks.

Peteski, nevermind.  For some reason I didn't get it the first time i read it.  Just read it again and it was crystal clear! 

[peteski]

Peteski, nevermind.  For some reason I didn't get it the first time i read it.  Just read it again and it was crystal clear! 

Excellent!    I should still upload a schematic for both versions (so color blind people can build this handy tester).

[MK]

I think you should when you get a chance.  Just for reference going forward.