ESU 58941 LokSound 5 Micro Direct NMRA DCC Sound Decoder - Decoded
Last Updated 231223
Originally posted on The Railwire: A Forum for Modelers by user peteski, last updated August 03, 2023, 02:24:02 PM.
This information is shared by and republished here with permission of author.
ESU 58941 Loksound 5 decoder for "wide body" Kato locomotives
This decoder consists of the ESU Loksound nano decoder with E24 pin interface daughterboard, installed on a Kato-outline motherboard. This arrangement provides access to all of the nano's functions. There is also an on-motherboard amplifier circuit which converts AUX3 and 4 logic level outputs from the nano to full-power AUX functions.
The solder pads are well labeled, and for clean installs ESU included a +U (12V) pads next to each full power AUX output pad.
While my worries are likely unfounded, I'm concerned about the way the bottom of the decoder is laid out in the area of the track power pickup strips. The metal strips in the locomotive will be right against the bottom sides of the decoder where traces are located on the decoder board. In addition tot he typical solder mask coating, ESU applied a layer of off-white coating which is supposed to act as insulator, but for extra protection Kapton tape could be applied to the orange-colored areas. However the extra thickness of the tape could prevent solid contact between the metal pickup strips in the loco with the exposed gold plated pads on the decoder. Use your own judgment as to whether to apply the Kapton tape.
Judging by the arrangement of the solder pads it appears that ESU dedicated the AUX 10 logic output for the ESU PowerPack control. Remember to use LokProgrammer to assign AUX 10 as Power Pack Control. For 2-wire keep-alive installs just use the GND and +U pads.
I was also surprised that ESU actually installed a 0.01 µF capacitor in parallel with motor pads. It is there likely for RFI suppression. Usually decoder manufacturers recommend removing RFI suppression components (capacitors or inductors) from the motor circuit. Obviously ESU engineers determined that using this capacitor will not negatively affect the motor operation.
ESU included 3900 ohm (3.9k) resistors on all the powered AUX outputs. With a typical white LEDs (Vf=3V) and +U=12V, that will result with (12-3) / 3900 = 0.0023A or 2.3mA of current passing through the LED. While this might result in desirable brightness of the LEDs, there are workarounds which will increase or decrease the current.
To lower the current (increase the resistance), just add another series-connected resistor to the AUX output pad. The total resistance will be 3.9k plus whatever additional resistors value is. For example, adding a 1k resistor will result in total resistance of 4.9k.
To lower the resistance, there are couple of ways to do it. Due to the small size of the resistors, good soldering skills, steady hands, and soldering iron with fine soldering tip are recommended. I also should mention that any modifications to the decoder void the warranty.
To totally bypass the on-board resistor simply solder a short length of small wire (shunt) across the resistor's end terminals. The resistor can remain on the decoder. Just place a piece of pre-tinned bare copper wire on top of the resistor and with a tiny bit of solder tack the wire to the tops of the resistor's metal terminals. Adding tiny amount of flux to the resistor's ends before soldering is helpful in getting a quick and clean solder joint. I would use a longer piece of wire to be able to hold on to it while soldering, then trim the excess length after the wire is soldered. Very thin bare wire will work well (like a single strand from a piece of insulated stranded wire. Now an external resistor of any value can be added in series with the AUX solder pad.
For a cleanest and most compact install, another resistor can be piggybacked over the existing resistor. For a total new resistance of 1k (Actually 918 ohms) piggyback a 1.2k resistor.
Few other examples: piggyback 1.8k resistor for a new total resistance of 1.2k. Piggyback 2.2k resistor for a new total resistance of 1.4k. These examples use standard resistor values. If someone wants to get other total resistance value, there are resistors available with a wider range of resistance values. There are also online parallel resistor value calculators available on the Internet. All the on-board resistors are SMD 0603 size, so the piggyback resistor should be the same size.
Dimensions of the decoder are provided in case someone would like to install the decoder in a model not designed to accept this board.
While I have not tested each install, I was told that these will fit (thickness wise) in pretty much all Kato locos which use that outline light board. E-units, F-units, F40PH, SD45, etc.
UPDATE: In this post Kelly warns that Kato PA1 and PB1 locos do not have enough vertical clearance for these decoders.
CAUTION: Like with similar drop-in decoders from other manufacturers, it is vital to insulate the motor lead strips to prevent them from touching the metal track pickup strips on the top of the chassis. If not properly insulated, the motor driver on the decoder will likely burn up (regardless of any over-current protection built-in on the decoder). I always found this to be a poor part of the Kato's design.
I'm surprised that ESU does not provide better technical documentation for their excellent decoders, compelling me to create these write-ups. Their documentation is not only sorely lacking technical details, it is also incomplete (at least the English version, since I have not looked at the German documentation). It is as if they expect their customers to be quite familiar with electronic circuitry (a skill that most model railroaders do not posses).