Model Railroad help

Thread Starter

maassmi

Joined Oct 30, 2011
81
I am worried about two things when comparing your bread board sketch, you lates simple skecth and what I have built, as I sketched out. My worries are:

1) The middle 1N4004 that is on my board as pictured and was in your earlier bread board schematic is no longer pictured in your last sketch;
2) LED placement, did I get it right?

Which way do I go before I finalize my board and solder it?
 

SgtWookie

Joined Jul 17, 2007
22,230
I left out the one diode trying to keep the circuit simple.

I already commented on the LED; the connection between the resistor and the LED should not be flopping around loose. All connections should be made on pads on the board.
 

Thread Starter

maassmi

Joined Oct 30, 2011
81
The wires aren't actually long like pictured. They are as close together as I could get them to the bread board. I will snip them when I go to solder them on the back or bottom side. Or I can remove them from the bread board when I solder them and use heat shrink tubes to cover any exposed wires as I put them together. I just would like to know whether I got their placement order correct please?
 

Thread Starter

maassmi

Joined Oct 30, 2011
81
This is my understanding:

1) I can remove the middle diode;
2) So long as exposed wires on the surface do not come in contact with each other (nothing loose or wiggling around), the board is good to go?
 

Thread Starter

maassmi

Joined Oct 30, 2011
81
Test results:

1) The LED did not light up;
2) Got one quiet click from the switch motor;
3) Nothing else happened except one of the LEDs from my existing turnout switches did not change from one color to the other when switched. Once I disconnected the CDU board, my existing LEDs functioned properly.

Oh well, it was fun trying. I am sure that something went wrong on my end of the project, like my soldering job. LOL At least I tried. Again, it was fun.

Thank you everyone for your help and special thanks to SgtWookie.
 

SgtWookie

Joined Jul 17, 2007
22,230
Take a photo of both the top and bottom of the board, and attach them to a reply using the "Go Advanced" and "Manage Attachments" buttons.
 

SgtWookie

Joined Jul 17, 2007
22,230
You have the positive side of the electrolytic capacitor connected wrongly; it's on the positive rail.

It should be connected to the emitter of the TIP120. You missed it by 1 hole. Connecting it to the positive rail will cause it to charge VERY slowly, and only reach about 1/2 the voltage it would normally be; as the LED's current would limit the maximum.
 

Thread Starter

maassmi

Joined Oct 30, 2011
81
Good catch, I will heat it up and move it in a couple of days and try again. It is getting late and I am expecting company tomorrow, so I probably won't work on it again until either tomorrow afternoon or Friday sometime. Thanks for the second set of eyes...
 

SgtWookie

Joined Jul 17, 2007
22,230
Your soldering definitely needs help.

You should be using 63/37 solder; that's the best. 60/40 is useable, but not quite as good.
You need to use 90% or better isopropyl alcohol to clean parts & the board with right before you solder, or you'll have the mess you're seeing. Parts and board must be clean and bright, and free of contaminates like finger oils.

You can buy 90% isopropyl from places like Wal-Mart pretty cheaply. Don't use the 70%, it has too much water in it and it takes forever to dry. Ace Hardware sells 99% isopropyl alcohol which is much better. Isopropyl alcohol is hygroscopic, which means it absorbs moisture from the atmosphere, so keep it tightly capped when not in use. It's also flammable, and burns with a nearly invisible blue flame. I use an acid brush to swab the alcohol around with. Acid brushes have black nylon bristles, and a rolled sheet metal handle. You can use cheap artists' brushes if you want, but I like the acid brushes, and you can get them at auto parts stores.

Your soldering iron tip is dirty. Clean it using either a copper or stainless steel scrubby pad; you can get them in a grocery store in the cleaning section. Get some 3-m Scotchbrite(tm) pads while there; they are excellent for removing corrosion and gunk from the leads of components and board surfaces. If your soldering iron is not clean and tinned, you will have a terrible time trying to solder anything.

Your iron is not hot enough. Check to make sure that your tip is on snugly. I have an inexpensive iron that has an adjustable heat tip; MPJA sells them for $15. Radio Shack sells an iron that is dual temp, 15W/30W, for around $7. It's not great, but it works for awhile. I never try to solder with the 15W side; I use that for standby to keep it somewhat warm, then kick it up to 30W a minute or so before I start soldering.

Use just a bit of liquid rosin flux; Radio Shack sells it. If your parts, board and solder are spotlessly clean, you really shouldn't need flux - but just a little bit will help ensure that you get a good joint.

Apply heat to both the wire and the copper pad at the same time. Then apply the solder to the pad and the wire, not the iron. The solder should flow like water, and the joint should be bright and shiny when it cools. If it is not shiny, there is a good chance that you moved the board or the wire when the solder was in the "plastic" state; the joint will be crystallized, it will be weak and have a lot of resistance.

If your soldering looks like a slag heap, you know you're doing something wrong.
 

SgtWookie

Joined Jul 17, 2007
22,230
OK, enjoy your time with your company.

When you get back to it, you really ought to remove the big globs of solder and the cruddy-looking stuff. Heat it up for a moment, and tap it on something - have an old rag underneath to catch the solder.

You can buy solder wick which works great, but it's getting pricey nowadays.
 

SgtWookie

Joined Jul 17, 2007
22,230
Checklist:
63/37 solder - Radio Shack or electronics store
Liquid rosin flux - Radio Shack
90% or better isopropyl alcohol - Wal-Mart, Ace Hardware, Home Depot
Acid brushes - auto parts store, hardware store
Copper or stainless scrubby pad - dollar store, grocery store cleaning section
3-M Scotchbrite(tm) pads
Solder wick or solder sucker - Radio Shack or electronics store
Clean & tin soldering iron tip; make sure it's on snug
 
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