From Kenneth Pallund :

The 6090 Digital Decoder:

The 6090 is märklin's old top decoder.

What you get is a permanent magnet and a new 5-pole rotor. The decoder itself has tiny

potentiometers which allows for adjustment of max/min speed and delayed acceleration/braking.

The decoder can also, use all 80 addresses. With the upgraded motor you have a very

powerful machine, which runs smoothly even at low speeds.

I suggest you tweak the potentiometers one at a time & one will give you slow to max speed & the other a quick or delayed stopping distance.
Let us know how you go. You really don't want to go back to analog.

https://wiki.3rail.nl/index.php/M%C3%A4rklin_6090_Decoder

Thanks for the replies Dave and John,

The motor does have a permanent magnet so I guess it is a 6090 decoder. I was just surprised that the max speed potentiometer doesn't alter the max speed in analogue mode whereas it does on a couple of other locos that I have with the same or similar decoder. Other than that the loco runs fine just slow.
I will try it on a bit of track with a digital controller as I suppose there could be something wrong with the decoder.

I tried a digital layout years ago and lost interest quite quickly - I prefer the 'classic feel' of the older analogue stuff.

The decoder you have was available as a 60902 (same decoder as in the 60901/903/904 kits)

It was designed to run with the 5 pole c90 motor, and you have it running with a large flat commutator with a Hamo magnet. I suspect this is the reason for the poor performance.

You have two options as I see it. 1. Restore to analogue with a replacement field magnet and reversing unit. Or 2. Upgrade the motor to a c90 with the 60944 motor kit.

If you do option 2 you will get much improved running with smooth acceleration etc, and it will perform well in analogue..

Cheers….

Mike

I have a reversing unit, and I’d be happy to swap for the decoder, but I am in NZ, Aand the postage may be a bit high. I could check in the new year if you like?

Put all dip switches to off and the 6090 functions are bypassed. That's how I run an old santa fe f7.

MVD71 - that's good of you but, as you say, the postage each way would probably be more than the parts are worth. It's a small world these days but so far no one has told that to the Post Office!
I still keep a few digital locos just in case so this decoder will get used for its proper purpose. Thanks though.
I don't think this was originally a Hamo model as I have the box - that doesn't mean it's the original box though so it may have been.

Ben - this one seems to work in analogue whatever position the switches are in. I tried them all off and it didn't make any difference - still ran ok but still slow.
I think the older 6080 and delta decoders need all the switches to be off.

Alan - I also collect Hornby Dublo from the fifties so I am quite familiar with the symptoms of weak magnets. They are Alnico magnets and tend to lose a bit of strength if the motor is dismantled. I have a remagnetiser for servicing.
I hadn't heard that about Hamo magnets but if others have found it then it must be an issue sometimes. This one seems ok (at the moment!). The motor draws about 270mA which I think is ok. I think the ESU ones are Neo but I don't think the Hamo ones are. It's something to keep an eye on, thanks for the heads up.

I bought a Hamo croc used in 1992, took it home, and it began slowing down aftyer runniung about 10 minutes. It belonged to a termianlly ill docotr. My dealer fixed it N/C for me. He said he cleaned and lubed the commutator and it was 100%. No trouble since. I put a 5 pole armature in my Hamo SBB RE 460 and it runs like hell.
Is it possible if room in the loco body allows for, to piggyback another magnet onot the Hamo one?

If you keep some digital locos, then I would suggest getting the correct motor for the decoder, then it will work well in both analogue and digital.

Sounds like a good result then :-)