Hello All,

Can someone please exlain the following strange issue:
As recommended in the Marklin digital handbook, I installed 1.5k resistors on all isolated track sections longtime ago. I also installed "track occupation" detectors, in combination with s88 decoder, as outlined on the following website: http://www.heise.de/ct/R...cm/buch/digit_8.html#GB8

All worked fine for a long time. Even when a loc is in the isolated track section (f.i. before signal), still a "track occupied" signal is given, detected through the small current flowing through the resistor.

However, some time ago I bought my first loc with a 5 pole motor (green persil dampfspeicherlok) which is acting strange in this setup (I only had 3 pole motors before). This specific loc makes a soft but anoying whistling sound while entering the isolated track section. After some experiments I changed the 1.5k's into 4.7k's. Result: whistling sound almost disappears, isolated loc still listens to commands from 6021 and "track occupation signal" is still working. When going to higher resistor values, track occupation signal is no longer given.

I asked Marklin where this whistling sound came from and if it could hurt/damage the decoder, but all they answered was that I had to remove the resistors to make the whistling disappear. No further explanation.

But then my track occupation will not work any more. Question to this forum: I am still wondering where the sound came from and if it is hazardous.

By the way: It can't be that bad, because the system works for half a year now without problems.

Regards,

Hans

Hi Kevin,
I think you are right, they are not 'needed' for modern decoders. However, to me it appears that Hans has another use for them, to detect track occupancy. But I have no clue to his problem, listening with interest...
/Lars

Hello everybody.

Thanks for your reply. Here are some return comments.

- Yes, I still have about 10 loks equiped with "old style" decoders that need the resistors for preventing a memory loss. Replacing them by new 5 pole ones would be very nice, but simply exceeds my budget. There are nicer ways to spend my money to my opinion. Again, using 4.7k resistors works fine instead of the 1.5k ones.

- at the time I started my layout, I still had a 6020 (bought way back in the eighties). Just recently when I got my first lok with additional functions I bought myself a 6021.

- The nice way of using the described track occupancy detectors is that they can be easily retrofitted on existing layouts without changing track sections. I have primarily the old metal track and this way of detection works perfect with that type of track. Isolating single rails is not easy on M-track. Last but not least, this occupancy detector costs less than 1 euro per track section, including self made print circuit. Also the s88 decoders (or should I say encoders) are self made.

So basically the existance of the resistors is not so much a problem. The described way of train detection is highly preferred and recommended by me. I am just still wondering where the noise comes from and if it can do any potential harm to the decoder or motor.

By the way, it is strange to observe that marklin advised to use the 1.5k resistors in its digital handbook when in the same book the use of a 6021 + the new decoders were mentioned as well. No single line about the need of removing them while replacing the 6020 by a 6021.

Regards,

Hans