Installing alternate SMD LEDS on TCS K1D4?

[MetroRedLine]

I have a Kato SD70ACe that uses a TCS K1D4 decoder. A couple years ago I accidentally snapped the front LED off with a screwdriver trying to remove the decoder.
It was a blessing in disguise though, because the decoder's stock SMD LEDs emit the "cold white" blueish LED glow, which is a total letdown, and I thought about replacing the stock cold white LEDs with warm white ones.

I have some 3v warm white  SMD LEDs, can I just solder these directly onto the front/rear LED pads on the bottom of the decoder, or do I need a resistor to tone down the voltage? And if so, which pad has the positive polarity?

[peteski]

If the original LED was a white LED then you can just solder your warm-white LED to the same exact pads the original LED was on.  White LEDs  all have very similar properties, so one can be substituted for another one (the decoder already has some on-board means of limiting the LED current  -probably a resistor).

[wvgca]

warm white and cool white are very similar... and can readily replace each other .....
if you find the origional, or replacement light is 'too bright', you can solder in an -additional- resistor, a suggestion would be in the range of 300 to 500 ohm additional .,
the positive lead can easily be identified on the led by
1] the positive lead is slightly longer, good on new ones, not so good on installed ones ..
2] the negative lead is identified by a flat spot on the body of the led, that's the negative lead ..
3] there is a 'hammer / anvil' internally on the led .. the smaller part [hammer] goes to the positive..
smd leds are similar ..
it doesn't matter which lead the resistor  goes on, but usually is on the positive lead

[MetroRedLine]

warm white and cool white are very similar... and can readily replace each other .....
if you find the origional, or replacement light is 'too bright', you can solder in an -additional- resistor, a suggestion would be in the range of 300 to 500 ohm additional .,
the positive lead can easily be identified on the led by
1] the positive lead is slightly longer, good on new ones, not so good on installed ones ..
2] the negative lead is identified by a flat spot on the body of the led, that's the negative lead ..
3] there is a 'hammer / anvil' internally on the led .. the smaller part [hammer] goes to the positive..
smd leds are similar ..
it doesn't matter which lead the resistor  goes on, but usually is on the positive lead

Unfortunately nothing you mentioned applies to this TCS decoder; as I mentioned the LEDs on the decoder are SMDs (Surface Mount Device), which means it has no bulb and is installed directly on the decoder board with no leads. At the bottom of the decoder there are metal pads directly below the SMD, but no markings as to the polarity.

I'd like someone who has direct experience with TCS decoders to chime in.

[peteski]

LOL!  I thought you were simply going to solder the new LED to the pads where the original LED was soldered.  What does the manual sheet for that info state about those pads?

[MetroRedLine]

LOL!  I thought you were simply going to solder the new LED to the pads where the original LED was soldered.  What does the manual sheet for that info state about those pads?

The manual says nothing about the front and rear LED pads, only the extra function pads towards the middle of the decoder for additional light features. Those are 12v DC and share a common +. Being that most SMD LEDs are 3v or 1.5v, I assume there's already a corresponding resistor built into the board, but I just want to know for sure.

[peteski]

If you were to post sharp and clear closeup photos of the top and bottom of the decoder, there is a good chance I should be able to figure out whether there is a resistor in their circuit or not. Or wait until somoene who is familiar with the decoder chimes  in. 

[MetroRedLine]

If you were to post sharp and clear closeup photos of the top and bottom of the decoder, there is a good chance I should be able to figure out whether there is a resistor in their circuit or not. Or wait until somoene who is familiar with the decoder chimes  in. 

Photo of the K1D4:

[peteski]

This doesn't show the back of the decoder, so I don't have the complete picture.  The 4 function pads on the narrow part of the decoder appear to have 1k ohm (marked 102) resistors connected in series. So you could attach LEDs to those directly (no extra resistors).

I'm still not sure which pads are you planning on using for the external headlight LEDs.  I don't really see any other pads there.

This is what I see in that photo and what I think the pads' functions are.
Ones marked with "?" are likely used for factory programming or testing the microcontroller - not used in normal operation.

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[peteski]

@MetroRedLine , I see you started a new thread about another decoder project. Did you abandon this one?  I did try to help . . . it would be nice to hear whether the info I provided was helpful or not. 

[MetroRedLine]

@MetroRedLine , I see you started a new thread about another decoder project. Did you abandon this one?  I did try to help . . . it would be nice to hear whether the info I provided was helpful or not. 

Yes, I abandoned it. Curiosity killed the cat, as well as my decoder. But at least I found out which side was positive (the fireman's side of the decoder facing forward).
Unfortunately, I think the solder at the bottom pads of the decoder either came in contact with the frame, or seeped into the adjacent frame contact pads. I think I need a more finer tip on my soldering iron.

Since repairing a decoder is going to be more trouble than just buying a new one, I'm going to get the Digitrax version of the decoder instead of another TCS, because at least I know that one has the warm white LED (I have one on my UP yellow Kato ACe).

[peteski]

Ok, thanks for the follow up.

[peteski]

MetroRedLine (MRL) send me his "sick" decoder couple of months ago and I just got to it last week.

I first examined it visually, and except for the damaged front LED pads I did not see any obviously damaged or fried components.  Using alligator clips I hooked a motor to the decoder, and then the decoder to my NCE Power Cab.

Using programming track mode I was able to read and write the CVs.  The decoder had a 4-digit address decoder configured (I think it was in a 900 or 9000 range).  I decided to just reset the decoder (usually the first thing I do before starting any troubleshooting).  Wrote "2" to CV8, then power cycled.
Now I tried running the decoder on main line using short address "3". The decoder responded., I was able to control the motor and the (rear) headlight.  The decoder was good.

Since MRL asked me to fix the headlight and replace the rear headlight using warm white LEDs, I removed the bluish white rear headlight and installed my favorite warm white LEDs.  They are SMD devices, but larger than the ones usually used on N scale decoders. Their color temperature is around 3000K (similar to halogen incandescent headlights in modern locos).

I also noticed that MRL added some solder to the frame contact pads to increase their thickness. I removed the solder and in its place I soldered small rectangles of 0.004" brass.  If those end up being too thick, they can be easily unsodered and replaced with just solder, like they were before.





I mailed the decoder back to MRL.  I'll PM you the tracking #.