beatmania IIDX Lightning Model Turntable resistance adjustment (MRF Device) repair log

Update:

Boss bought a new one, replacing the one I fixed.

Demo: https://x.com/mnm_isola/status/1855575552473579789

As you can see the brand new one is might tighter at the max resistance setting.

The old one is sold to somewhere in Taiwan, probably installed in a cab.

                                          

Update 2:

Have some thought after watching this videos and I think I should update this essay for a more accurate information.

The keyword here is "Magnetic Particle Clutch", which explains what the powders are inside the MRF device.

So I bought a bottle of powder with the intention to mix the iron powder into the stock MRF devices but if I fuck up I would be 8900HKD in debt so uuhhhhhhh.

Try at your own risk.

                                          

Some background: This particular cabinet was originally in Hong Kong until X-Land went kaput during COVID and the cab was sent to Macau, I currently work in the arcade it's in and the maintainer of these machines.

At some point (probably 2~ish years since we have the cab) I found out when playing IIDX that the 1P turntable has a weird ununiform resistance at some spot, and even dead stops and bounces back when freespinning. After some digging around, apparently it was the "MRF device" that was causing it. The spindle just get jammed at some certain angle.

Okie then, problem found, replace the part and good to go, right?

The part in question Kurimoto MRF-B2SK (Konami Ref. Number: 117191080000 MRF DEVICE). Konami sent us a quote of 8900HKD/ea (~1110USD), gonna break the bank. Kurimoto doesn't sell their products to individuals either. There are also no alternative MRF devices on the market that we could get a hold of. Konami basically has the monopoly on this part. The only options I have is to either fix the broken MRF myself, or buy a new one.

                                          

Update: This is much more relevant than the explanation I had written.

Magnetic particle clutch

So what is this MRF device?

Basically it's a magnetically responsive liquid that thickens when a magnetic field is present. Think of those ferrofluid video you see on Youtube. You get a metal cylinder, throw in some MRF liquid, an electromagnet, a disc attached to a spindle and bam, you get a more or less MRF device that we're talking about, now you just have some form of controller PWMing the electromagnet and you'll have variable resistance for the turntable.

* Credit goes the the Cons&Stuff community

                                          

This was gonna take some time for me to figure out what went wrong, so I just swapped 2P's MRF to 1P since it has less usage, and have the MRF removed on the 2P side. Since the part that actually provides the resistance for the turntable is gone, I had to make it up with something else or the disc would spin way too much and it'd be very hard to play. I just went with the old IIDX cab's method of using felt (in this case I chose to use some thin cotton wipe sheets, fold until the thickness is right).

After tightening the 3 screws holding the top part (and also some pushing and pulling onto the shaft while tensioning), I figured it was the little metal disc attached to the spindle that was pressing way too tight into the base of the MRF housing, which made it very difficult to rotate, since it was just rubbing onto metal.

Be careful when using a screwdriver with a magnetic tip, some of the iron dusts might get stuck to the tip and you lose some of the content from the MRF device (making it less tight).

1st solution: Don't tighten the screw on the housing -> the problem eventually came back.

2nd solution: Since I already knew it was the metal disc inside the unit that was jamming (albeit for unknow reasons), I sprayed WD40 onto the disc, use paper tissue to suck out the excess WD40, reassemble the MRF unit.

You are definitely not suppose to mix the metallic dust substance in the MRF unit with other liquid (especially WD40, it's more of a cleaning agent before it's a lubricant) but not like I have a choice anyway, thing was already broken, ain't got more stuff to lose, YOLO.

I did said MRF device uses fluid for its purpose but I didn't found any of those MRF fluid in the cylinder, only metallic dust, and the spindle and the disc is also not in any way attached to the lower compartment, weird. The bottom half seemed to be sealed (or it's friction fitted very tightly), I also don't have any reason to go further since the problem is fixed and I need it in service ASAP, so I didn't dig further.

I assume the bottom part is just a electromagnet (similar to the Arduino ones?).

FYI Kurimoto MRF-B2SK seems to take DC 5V, generic industrial ones seems to range from 12/24/48V. 

seems to be working fine for now

until then