Back to the reason this thread was started.
UPDATE: In March 2018 I have updated this post to include the of the function mapping of the (AUX) outputs at the bottom of the post. I have also created a separate thread (in the DCC/Electronics section) covering this decoder, and also ESU 54650 and 73100 See
https://www.therailwire.net/forum/index.php?topic=44324.0John asked me to figure out the best spot for attaching stay-alive capacitors or a keep-alive module.
I cleared some room on my crowded workbench to do some snooping around the decoder's circuitry. Many of the components are tiny, and so close together, that I had to construct couple of really fine probes. I used sawing needles for the tips and a flexible 30AWG decoder wire for the leads.
ESU_NeedleProbes.jpg
Here are my findings.
ESU_73199_Sound_decoder.png
For those who are interested I also drew a partial schematic diagram of the decoder. This decoder's design is different and more complex from other sound decoders I have dealt with in the past. It has a power supply circuit with 3 voltage stages where a stay-alive caps or keep-alive module could be hooked up.
Stage 1: Raw rectified track voltage (marked "A" or RED on the diagram). This stage supplies power to the motor driver circuit and to the next voltage stage (described below). This is where one of the Super-Cap-based keep-alive circuits could be installed to keep both, the decoder's electronics, and the motor running during power dropouts. This stage includes what looks like a Zener diode (for over-voltage protection?) and a very small ceramic capacitor (probably less than 1uF in value, to shunt any voltage spikes coming from the track).
Stage 2: (marked "B" or PURPLE on the diagram). The voltage from stage 1 is passed through a diode (same type of diode as used in the rectifier) to become stage 2. This stage has five multilayer ceramic caps used as a small stay-alive circuit (totaling probably around 200uF, but since they are unmarked I don't know their exact value). The voltage from this stage is then supplied to stage 3, and probably to few other circuits on the decoder (I didn't do a thorough trace to check what else is powered from this stage). As shown on the diagram, the voltage in this stage is just few tenths lower than the raw rectified voltage of stage 1.
Stage 3: (marked as "C" or BLUE on the diagram). Voltage from stage 2 is supplied to a 5.4V regulator which produces the stage 3 voltage. There are couple of 100uF tantalum caps in this stage to act as a filter/keep-alive. This stage supplies power to most of the decoder's circuitry, including the audio amplifier. There are also couple more voltages derived from 5.4V. One is 5.1V (not sure where it is used) and then 3V which powers the "brains" of the decoder (the microcontroller and the Flash memory chip). The voltage from this stage is also used as the common positive for all the on-board AUX functions (including the V+ solder pad). It appears that the designers of this decoder decided to use the 5.4V as the BLUE common-positive (instead of the usual 12V used on majority of other decoders).
The tantalum caps in stage 3 (200uF total) do provide minimal protection from short-duration power dropouts, and there is around 200uF worth of capacitors in stage 2, so we can't really say that the decoder has no stay-alives. But all of this results in an absolutely bare minimum of the stay-alive capacitance.
Ground (common) of the decoder is marked on the diagram as "N".
Where to attach stay-alive capacitors, or a keep-alive SuperCap module?The bottom part of the diagram above shows both sides of the decoder with color-coded locations of where the external caps can be installed. The green circles indicate that the large copper areas are all connected to ground (common).
A capacitor can be installed with its negative lead attached to any of the green-marked areas or component pads. The positive lead can be hooked up to any of the red-marked pads (for stage1), or purple-marked pads (for stage 2). While I also show a pads for stage 3 (blue-marked pads), I do not think that any additional caps installed in stage 3 will be helpful.
When adding a true Super-Cap-based keep-alive circuit (hundreds of thousands of micro Farads with its built-in ancillary circuitry to limit the charging current and voltage) it should be attached to
green and
red marked pads of the decoder. If placed there, it will power the decoder's electronics, motor and the function outputs. Since the RED pads on the decoder are very small and close to other components, one must be super-careful not to damage any components while adding the keep-alive circuit.
If the additional caps are less than 1000uF in total capacitance then my recommendation would be to attach them to the
green and
purple marked pads of the decoder. Since the current-robbing motor is not powered from that stage, the keep-alive cap will supply power to the decoder for a longer time. Hopefully the flywheels will keep the loco coasting through the intermittent contact spot while the decoder keeps on running and producing its sounds.
Of course, any modification to the decoder are done at your own risk - it is highly miniaturized and delicate.For those interested in more details, here are the locations of some of the decoder's main components.
ESU_73199_Sound_decoder_layout.png
I found it interesting that the rectifier diodes used in this decoder have a very low forward voltage drop (only 0.2V). But I only tested it with minimal load so the voltage drop will most likely increase as the current draw increases. Still, they are probably Shottky diodes with the average voltage drop of around 0.5V or less.
MAP OF THE FUNCTION OUTPUTS AND THEIR SOLDER PADS
ESU_73199_Sound_decoder_functions.png
The above picture is self explanatory.
If someone wants to simply relocate the on-board LEDs while still using the on-board 680 ohm resistors, then simply unsolder the SMD LED from the PC board, then solder the wire lead extensions to the LED pads. The LED polarity (anode or positive [A] and cathode or negative [C]) is indicated in the picture.
Instead of calling those outputs "functions", like most DCC manufacturers do, ESU calls them "AUX" outputs. This is likely due to the fact that all these outputs can easily be mapped to any DCC function. The mapping feature on the ESU decoders is much more flexible than on most typical DCC decoders from American manufacturers. I highly recommend thoroughly reading the ESU decoder manual to get familiar with AUX output mappings. While the mapping can be done by individually programming a bunch of CVs on DCC system's programming track, this task is made *MUCH* easier using the ESU's LokProgrammer interface and software.
I hope that this answers your questions John.
