SOUND AND REPLACEMENT DECODER FOR LGB KOF 20930

[TONYWARD50]

Let's get one thing straight - as you may have seen from previous posts my sanity is somewhat in question.
I have just acquired a new KOF from Sir Jeremy of Pontardulais.
I would like to add sound.
I use ESU decoders and sound units mainly and have a spare ESU sound decoder/unit to hand.
I know there is already a Massoth chip in the loco but I agree from the other posts on this site that if you fit the standard speaker there is no where to put a Massoth S sound chip. So I was contemplating replacing the existing decoder with an ESU Sound. I could then put a larger speaker in the cab, which would be mainly hidden by the driver, or would be completely hidden if there was a second man on board.
Question - this loco uses LEDs, so I know I have to be careful when connecting them to a new decoder, so how do I check polarity and what voltage are the LED's ? Do I need any resisitors or can I use what is already in the loco ?
Lastly, am I completely off my trolley and would I be better just getting the Massoth S Unit ?

Yours,
Worried of Dorset

 

[Gizzy]

Checking LED polarity;

the only way I can suggest with the lighting in situ, is to connect each one in turn to the appropriate terminals on the decoder.

(As Ross mentioned, you may need a suitable bias resistance.)

If it lights up, all is well, if it doesn't, swap the 2 wires around.
(It is a Light Emitting DIODE, allowing current flow in one direction, after all!)

If you get nothing, then you've popped the LED! But this shouldn't happen if you use a bias resistor.

Good luck....

 

[Gizzy]

Another way of checking LEDs;

there is normally a flat side on the 'rim' of a LED, which is the cathode, or negative lead.

http://en.wikipedia.org/wiki/File:LED,_5mm,_green_(en).svg

The diagram as per the linky above explains it much better than I....

 

[Zerogee]

Hi Tony, I assume you've read my posts about installing the S unit in my KoF? Though it's not the perfect solution in that it still has to go in the cab, I really do think it's the best and easiest option. If you're thinking of putting a speaker in the cab, then that is going to be much more visible than tucking the S unit down the side as I did.

However, having said all that, if you already have the ESU decoder spare, then you may as well use it! If you do, please take some pics and write it up for the forum so we can all see how it goes!

The LED lights in the KoF are not separate dome-shaped conventional LEDs, they are tiny micro ones built onto little squares of circuit board - frankly I'd leave these well alone, which is another very good reason for keeping the onboard factory decoder as it is. If you do want to re-wire them, I have a suspicion that there may be resistors build into the little circuit boards already - it might be best to do a readout of the CVs on the onboard decoder before you take it out, to see what voltage it is feeding to the lighting outputs - then you'd know what you need to do with the ESU decoder to match them.

Jon.

 

[Zerogee]

Another way of checking LEDs;

there is normally a flat side on the 'rim' of a LED, which is the cathode, or negative lead.

http://en.wikipedia.org/wiki/File:LED,_5mm,_green_(en).svg

The diagram as per the linky above explains it much better than I....

Trouble is, Gizzy, the LED lights in the KoF are not that kind - they are tiny little components on tiny squares of PCB!
If you look at my thread here:
http://www.gscalecentral.net/m12897... square is the cab interior light! Jon.

 

[Gizzy]

Another way of checking LEDs;

there is normally a flat side on the 'rim' of a LED, which is the cathode, or negative lead.

http://en.wikipedia.org/wiki/File:LED,_5mm,_green_(en).svg

The diagram as per the linky above explains it much better than I....

Trouble is, Gizzy, the LED lights in the KoF are not that kind - they are tiny little components on tiny squares of PCB!
If you look at my thread here:
http://www.gscalecentral.net/m128972
and scroll down to the fourth and fifth pictures, that little green square is the cab interior light!

Jon.

Yep Jon, I just had a look and I realise that this post is irrelevant in this case.

Also realised it's the new Kof loco like yours and not the one like mine.

Therefore, I bow to your superior knowledge and experience with this particular wee beastie!

 

[palmerston]

Resume:
LGB onboarddecoder
The voltage for lighting terminals is stored in CV50. It is most likely the value = 5 as this decoder is also used in models with conventional lightbulbs, thus being 5V. Most likely the bias resistors are on the small PCB holding the SMD leds. The original decoder saves rewireing the lighting. Have used the original terminals from Massoth or Champex-Linden for soldering an adapter print.