glad that it worked out good for you :)
Thank you to everyone who helped out! I just finished the soldering today, and tested the unit with the KA4. The DC Negative was right where the negative on Mark's diagram was. It runs perfectly, and the capacitor is really keeping the 0-4-0 alive. Again, I appreciate the patience, and hope that this thread works as a guide to those who want to install a Keep Alive on a small decoder!
-Khang Lu, University of Minnesota Railroad Club
No, the diode pins marked RED go tot he red wire, which is the track input. You want the diode pins marked + (which also go to the blue wire, so use that) and the ones marked -.
Do test first with a meter. You should get a DC voltage a little bit lower than track voltage between the blue wire and the pins marked - on the diodes. Not AC.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Thank you Mark! That helps clarify things a lot. Since I’m lookin for the DC Negative, should I just solder to the red diode marked red? Or the blue one? Also, I will certainly test it out with a multimeter.
I'd use to meter to be certain, but this looks to be the connections in the diode array to me ....
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
it would probably be easier to use a multi meter, set it on 20v DC, the red wire on the meter to the blue coming from the decoder, and try the other one from the meter where you had indicated ... you should get DC out about the same as DCC voltage ... about 14v to 17v DC
It goes to the other side, where it looks like there's a copper piece. This side should be it, since the blue wire doesn't go anywhere on the other side (the one not in the photo). That being said, it does appear that the red and black wires are soldered to the array from the other side, and the blue wire leads to the bottom left bridge piece. All four of these are connected. I see one, the top piece, that doesn't have a wire connected to one end of it. This is the piece that leads to the copper piece on the other side. Should I try soldering the KA4 to that copper piece? Or the bridge piece?
Thank you for your patience and help.
Well, it should have a junction, it feeds the negative side of the rest of the circuit. it just does not lead to any of the wires. If you look at a schematic foor a full wave rectifer, there are 2 AC inputs and 2 DC outputs. The two AC inputs are the red and black wires from the track pickups. The positive output is the blue wire, the other output is the circuit common, where the other terminal of the keep alive needs to connect.
The decoder boards are double sides - so while you might not see any connections on one side, there will be small holes called vias through to the other side, and the connection may be made on the back instead.
rrinker The final junction that does not go to the red, blue, or black wires is the one you want.
The final junction that does not go to the red, blue, or black wires is the one you want.
If the above is true to what I believe is the array, there is one diode that has an end with no junctions to it. Would that be it?
Thank you, that does help a lot. As for getting a KA decoder, the unit I'm installing this in is too small for most decoders, so I'm limited to a DZ123. As for wiring, I'm sure I can figure it out. Are the diode bridge components the ones shown in the photo linked above? There are 4 components and that was my guess.
The diode bridge is the 4 components immediately above the black and red wires. As to exactly which one you need to connect to - that requires closer viewing than you will get with a photograph.
The red wire should go to one junction between two of the diodes. The black wire should go to another junction between two of the diodes. The blue wire should come from a third junction between two of them. The final junction that does not go to the red, blue, or black wires is the one you want.
If this makes absolutely no sense - I would suggest replacing the decoder with one made for a stay alive where the stay alive will just plug in, or at least is new enough that the connection points are well documents.
Where is the bridge diode array? Here’s a photo of the decoder.
https://imgur.com/a/pPfkpJ5
the blue [positive common] goes to the blue wire on the decoder..
the black/white [negative common] goes to a negative / ground point on the bridge diode array .. no wire sticking out there , just some fine soldering right to the pad ...
Hello, has anyone had luck in installing a Keep Alive 4 into a DZ123? I understand that the blue wire on the KA4 would go with the blue wire on the DZ123 (common), but I don't know where the black/white wire on the KA4 would go. Thanks.