To get at the sliders (Treble, Bass, Balance) follow this thread, When you are here (pic), take of the cord for the volume wheel and take of the wheel, now we can get at all solder points

Now turn up the heat on your solder iron and desolder, using a desolder pump, the holding pegs for the poties, 6 pegs. Then starting with the treble, lower the heat and desolder the connection pegs, 7 pegs, now insert a small screwdriver between board and slider housing ends and wiggle a little to check if all pegs are lose, if not desolder until all pegs are free, take out the slider and mark it to get it back in the same place in the same way, looks like this, The pen is pointing to a plastic peg melted over the steel plate.

Now with a level cut pair of pliers, cut of the top of the peg.

To get of the rest of the peg, grab into your trouser pocket and take out your universal B&O tool, a small Swiss made knife, and cut or scape of the plastic until level with the plate. The black point in the pic below is the top of the peg that was cut of with the pliers.

Now wiggle and press upwards on the holding pegs and the steel plate comes of.

To get of the top plasic piece, its time to use your beloved Swiss made knife again, I allways buy 2/3 of these and keep 1/2 extra at home, when you travel to exotic places like USA and Banana Republic, the Under Assistent Security Officers, likes to take your Swiss made knife, if you forgot to put it in your checked bagage, in that situation I open the sharp blade and the combined file and screwdriver, on my trusted knife, and brake both of,  and with a satanic smile I handle the pieces to the Under Assistent and says "There you go, all yours".

Back to the thread before a monitor cancel it. squeeze the point of the knife in between the top piece and the end of the housing, wiggle or woggle until it lifts some 2 Mm. Be careful the plastic is old and brittle and brakes easy.

The housing has 2 knobs in the middle to fix the top in position, again use the point of your Swiss made knife and bend a little to free the top in the middle, in the pic the knife in far to wide in, I had to do it that way to be able to take photo, I have only 2 hands, and to complicate things I'm also left handed

Now woggle wiggle a little more and then pull the top piece straight up without bending the connection pegs to much.

Top of, look how dirty it is, this is the balance slider, the treble slider was worse, full with some green grease or goo, and after cleanng with Iso alcohol it looked nearly as this one.

Now we have everything out and ready to clean, I clean with Isopropylic alcohol (dont drink it it tastes awful) and pipe cleaners, when averything is clean, I polish the tracks and contact springs with white 3M pad cut to size, the white pad is less abrasive than the green 3M pad, then one more time with alcohol. The slider piece in these poties has 4 spring steel contact clips, I like these a lot more than the ones from the BM 2400, they are much better, the 2400 ones is copper plated but smaller and the slider where they are attached more fragile.

All clean and ready to assambly.

As one of the top pieces cracked a little around one of the mounting holes, I glued it with crazy glue and squeezed with a plier until it bonded. Put in the sliding piece put on the top piece, remember to press down in the middle to get the top piece all way in, (click, click) and if there are no cracks or broken pieces, there is no need to glue anything.

Check if the slider moves with a small resistance all the way end to end, and put on the steel plate, done.

This is the only way to clean and restore old potis this type, you can spray what ever you want into the slider, this will only move the dirt around and maybe work better for a short time, but will always come back with failures, crack buzz tick tick.

Assambled check function with your Multimeter, its a to solder it into place and find out that it doesn't work.

Ready to solder onto the PCB, that will be later today or tomorrow, its time for a cuba or 2 to celebrate a good done work, its very important to relax in between, when working this hard, so tell your wife or the girl to bring your cuba, a lot of ice, aged Rum and coke, enjoy

To get the poties into place again, start with the treble, before that clean all solder points and take care that all holes are free. Place the poti where it belong same way as when you took it out, now turn the unit solder side up, under the steel plate, at the end facing away from the Bass poti place the antenna holder, see pic, it fits perfectly into the housing and gives a little pressure on the plate to get it level with the board, solder first peg, move antenna holder to the other side, solder peg on the inside, same for the other potis, last solder all connection pegs, done. Be careful not damage volume, scale cords and cables while soldering.

All in, test, close unit and enjoy, with for example Edward Griegs Morning, from Peer Gynt.

Good job Soren. Glad to see you have the 901 back up and running again.

Other than that all I can say is, "God, I hate taking those things apart."

Eugene:

Good job Soren. Glad to see you have the 901 back up and running again.

Other than that all I can say is, "God, I hate taking those things apart."

Remind me never to buy one of those!  Of course I'm a wuss - I won't even work on a BM2400 or BM4000.

I am starting to get withdrawal symptons, though.  I need a new pair of speakers to work on!

@Eugene - how's the nonsmoking going?