Installing a Keep Alive capacitor in a BLI SW7

I have two of these locos which are about 10 years old. They are DCC with sound. I sent an e-mail to TCS tech support asking if one of their capacitors would work in my SW7s. Their reply didn’t give me specific instructions for this loco but did say I would need to figure where to attach the blue wire (common) and black/white wire (ground). I have no idea which wire should go where. The decoder has a 4 wire plug, black/yellow/green/red, which are wired to a smaller board under the roof of the cab. There is additional wiring under the decoder which is screwed in place above the motor assembly. If I were to guess based on my limited knowledge of these types of electronics, it would to be that the red and black wires in the plug are the power wires and that these are where the capacitor wires should be spliced to. But since I don’t want to guess, I thought I’d ask more knowledgeable people than myself how to procede. I need to know which wires to attach the capacitor to and where that splice should be made. Also there is not a lot of room inside the shell to put a capacitor. It looks like the only available space is inside the cab.

The other opion they gave me was to replace the decoders with one of the decoders with Keep Alive already installed. That might be the simplest solution but probably the more expensive as well.

Stay Alive leads have to be connected to the DC power on a decoder. Usually at the plus and minus output of the full wave bridge rectifier.

With shrink wrapped decoders, the blue wire, plus common and find a negative connection on the decoder board. The below site shows different decoder connection points.

http://www.members.optusnet.com.au/mainnorth/alive.htm

Rich

So if I am understanding this correctly, I won’t be splicing the KA1 wires into an existing wire but will be soldering them to a terminal on the decoder. I just have to figure out the correct one.

One other thing I forgot to ask in the OP. The TCS website says the following:

“All TCS decoders shipping with date codes from January 2012 support the Keep-Alive feature.”

Since these are not TCS decoders and are quite a bit older than 2012, is it possible they will not support Keep Alive?

I’m wondering if the better but more expensive solution might not be to buy one of their new decoders and install the old SW7 decoders in some of my non-sound diesels.

Try this web link - lots of good examples of using various sound decoders;

http://www.members.optusnet.com.au/mainnorth/alive.htm

Jim

BLI locos from 10 years ago will have a QSI sound decoder. If Marcus does not explicitly show a QSI decoder, the information presented there will point you in the right direction to find where you need to solder wires for the keep alive. This will not be soldering to a tab on the decoder, but soldering directly to a component on the board. I’d mention voiding the warranty but at 10 years old there’s no warranty anyway. If you are careful and use a good fine tip soldering iron this isn’t really a big deal, but if you don’t work carefully and take your time you could destroy the decoder.

–Randy

The website I looked at had instructions for two different QSI decoders, Revolution A and Revolution U. The A instructions had a picture that looked nothing like my decoders and looking at my decoders, there is no way I would attempt to solder to any of the tabs because they are way too small, much smaller than the connections in the picture.

The instructions for the U seem more up my alley. There are no pictures, so I can’t verify that is what I have but the instructions say to connect to the wires. This is the entire instructions:

QSI Revolution U

  1. Connect the BLUE wire to the BLUE decoder wire.

  2. Connect the BLACK/White trace

Yours would not be either of those. Revolution A is an Atlas/Athearn format board decoder and Rev U is a wired version of the same. Both are the products from QSI that came out after the ones used in the BLI locos.

It’s not a misprint, the Rev A and the older ones have a keep alive on board, but it only powers the cound portion of the decoder, not the motor. The Rev U has the cap attached to the decoder by wires. One side of it goes to the proper place on the decoder, so you can just solder to the wire.

The key to having a keep alive power the whole thing and not just the sound is, if you looked through the page, getting the keep alive attached to the main DC supply for the decoder, which comes right after the rectifier bridge. The blue + wire for functions is often attached to the main DC + source, but there is not normally a wire attached to the main - side as mothing needs that (except a keep alive). That then needs to be soldered right to the component on the decoder board.

–Randy

It sounds like it is anbody’s guess as to whether there is even a Keep Alive capacitor compatable with my decoders and where they should be attached.

It’s a matter of following the board traces from where the track pickups connect. The first components they should connect to would be either 4 diodes forming a bridge or a single bridge rectifier. It’s compatible, but you must find the main circuit + and - connections, and of course it won’t just plug in.

–Randy

This is response to the first question on this topic – could a current-keeper be installed in a Broadway Limited Imports (BLI) EMD-SW7 switcher to help avoid engine stalling when going over switches and crossovers. I have a BLI Paragon-2 EMD-NW2 switcher and this was a question I also had. I believe the inter-workings of these two engines are the same. From the comments related to this topic, the general consensus was a lack of space for a current keeper. To address that question, I removed the shell of the engine. To do this, first remove the 2 back handrails that go between the shell and the frame. Then looking at the bottom of the engine you should observe 2 front and 2 back tabs. Gently squeeze the shell at either the front or rear tabs and slowly pull up on the shell. Once the shell slightly releases, do the same for the other tabs.

Once inside, I observed there is a fair amount of space above the decoder at the back. Taking a few measurements, it appeared that a TCS KA1 Keep Alive (1.063" x 0.35" x 0.244") might fit and it does. The next issue was locating where to solder the wires. The information of an excellent site on current-keepers (http://www.members.optusnet.com.au/mainnorth/alive.htm) indicates that I needed to find DC-positive and DC-negative connection points. For this decoder with plug-in connections for everything, it was going to require taking DC voltage measurements using a multi-meter at the bridge-rectifier diodes. These are the square chips located near the large capacitor. With the engine on the a powered and circuit protected track, I was looking for a two solder points on the diodes that would supply +12 DC-Volts. Do not use to the + terminal of the large capacitor as a test point as this only supplies power to the sound system and not to the motor. However, the other terminal of the large capacitor can be used for the DC-negative as it shares a

The answer the original question (though it may have already been resolved, but I’m a new member to the hobby), in my experience, the best option is go with the smallest fomr factor decoder of a manufacturer of your choice. All of them have those.

This will give you some extra space compared to the bigger OEM decoders.

Secondly, the Keep Alive super-capacitors are usually not installed onto the decoder PWB, but made as a stand-alone unit. So you have to do your measurements and do some research what space you have and what

This is a reasonably sized 4-axle locomotive. I would not expect it to need a keep-alive if trackwork is properly powered, particularly frogs on longer turnouts.

I would first examine why you think you need or would benefit from a keep-alive. Do you have plenty of feeders and powered metal frogs? Loosely fastened track depending on rail joiners to maintain power for too far or long plastic frogs or unpowered frogs can lead to stalling. I was lazy at first, but finally got around to powering my frogs and noticed significantly better performance right away.

The original ones like this with the QSI decoder were pretty light - so they came with traction tire wheels so they could actually pull something. So they don’t actually pick up with all 8 wheels if the traction tire wheelsets are installed. Basically you can pull a reasonable number of cars for an SW-7 and suffere from poor power pickup, or get decent power pickup but have trouble moving a train that a smaller Bachmann 44 tonner can easily more.

–Randy

I started this thread 5 years ago although I had a different screenname back then. I have two of these locos and they do stall on my insulated frogs. I have Atlas #6 turnouts through the yard. If they are moving very slowly which is how I like to run them, they will sometimes stop over an insulated frog. At this point, powering the frogs is not an option I am willing to consider. I have a 12 track double ended yard plus additional turnouts the switchers must negotiate and I am not willing to go to the time and expense of rewiring them so that the polarity to the frog can be switched.

I also have the same problem with a BLI K-4 Pacific. I have traced that problem to not getting pickup in the drivers on the left side of the loco. It only gets left side power from the tender. I have taken it appart to try to see what the problem is but haven’t loc

As I said in another reply, I started this thread under another screenname five years ago and no, the problem has not been resolved. I bought some Keep Alives last year that were suggested by Tony’s Train Exchange but I have not gotten around to installing them. My problem is that when it comes to electronics, I am illiterate regarding many of the terms. Some of the explanations I have read as to how to wire them might as well have been written in Chinese. I need something along the lines of Electronics for Dummies. I am very much interested in your suggestion for simple schematics online but have yet to find any. Do you have one or two that you can recommend. Something along the lines of, “Hook the blue wire here. Hook the white wire here.”. All the instructions I’ve seen so far tell me I need to figure out which wire is which. That’s why the Keep Alives are still on the shelf.

Going to have to find someone who’s done it then. The closest thing to the simple explanation is the part of marcus’ page that shows you how to figure out the right part of the circuit for most any decoder. I’m not even sure BLI uses the same decoder board layout in each loco, so it may be very specific to the SW-7, so someone with a different BLI diesel might not be a help either. If I had one, I could probably figure it out. If you can get some good in-focus close up pictures of the decoder board - one showing the whole thing, and then perhapst 3 even closer of the front, middle, and back - I or someone else here might be able to mark the correct points.

–Randy

Just as a data point, I recently figured this out after not too much effort. There’s Larry Puckett’s excellent short version of what’s needed to know when dealing with keep-alives in his DCC Corner column (pg 54-55) in the October 2019 MR. I followed his suggestion to check out the websites that could be helpful, several which have been cited previously in this thread.

Finding the blue common + is easy and usually labeled and ready to use. The negative - common is trickier as it’s usually not labeled, especially in older decoders. There is an easy test to confirm finding the common - Negative, though. Put the red + lead of your multimeter on the blue common + Positive. If you have the correct point identified for the common - Ground, when you touch the black negative lead of the multimeter to it, the meter should read somewhere around 13.5 volts positive if you have the command station output set around 14.5 volts. Ths drop is due to the voltage drop across the bridge rectifier or “H” bridge, indicating you are in the right spot needed to connect the keep-alive’s negative lead to.

Many modern decoders may have a solder pad to make connection easier. That’s what I found when I shucked the Digitrax DN136D out iof its shrinkwrap. Turns out that the solder pad was right at one corner to make connecting the common - Negative easier on the tiny decoder.

The DN136D was already fitted into my Shay, so I just needed to make room for the keep-alive. The smallest Digitrax decoder with a plug-in keep-alive option was about twice the size of the DN136D, so the hack gives you options you wouldn’t otherwise have. However, if the process is too intimidating, it’s money well spent to have a functioning unit bought RTR. The performance enhancement is well worth the investment.

I don’t fully understand how that is going to tell me which is

If you have power to the decoder and are sure of the Blue + Positive that the red multimeter lead is applied to, then you probe for getting a the ~13.5 volt reading.

Then the question is can you solder the lead from the keep-alive to it? I lucked out and found a solder pad where I needed to attach.

On many of the pictured examples at those websites, the soldering was done to a PCB trace or to the lead of an attached component, making it a delicate task to attach a wire without unsoldering something else. Discretion is the better part of valor here. If it looks like it’s beyond your soldering skills, then even if you’re certain about the right spot, it may be best to try a newer decoder already set-up to use keep-alive.

If you have power to the decoder and are sure of the Blue + Positive that the red multimeter lead is applied to, then you probe for getting a the ~13.5 volt reading.

Then the question is can you solder the lead from the keep-alive to it? I lucked out and found a solder pad where I needed to attach.

On many of the pictured examples at those websites, the soldering was done to a PCB trace or to the lead of an attached component, making it a delicate task to attach a wire without unsoldering something else. Discretion is the better part of valor here. If it looks like it’s beyond your soldering skills, then even if you’re certain about the right spot, it may be best to try a newer decoder already set-up to use keep-alive.