https://www.alesis.com/products/view/usb-midi-cable

It costed me about 20€

You will not believe :
I believe it would not work but anyway I decided to put the MIDI plugs reversed, intead of the right connection of In>>OUT and OUT>>IN, I placed this time IN>>IN and OUT>>OUT.

      And surprise, It worked !!!  
      MIDI IN LED also blinks now when I play.

I just registered in this forum to thank this Beto-Music guy. THANK YOU! I struggled with the same problem for years and the solution was this ridiculous. Now it works like a charm.

I'm guessing that you meant a MIDI-to-USB adapter, to connect from a MIDI port on the keyboard to a USB port on the computer.

Even if this was true, I'm not sure why you would need to do it.  I mean, wouldn't it be simpler to just get a cheap USB audio interface that has a 5-pin MIDI IN jack, like the $59 Behringer?  It's a lot harder going the other way (i.e., getting a USB MIDI output to a 5-Pin MIDI output), and about the only cost-effective way of doing that is with a Kenton MIDI USB Host adapter, which costs a hell of a lot more than a cheap USB audio interface with MIDI.

       I got Roland Cakewalk UM-1G the manual on web, read it entirely, found driver for Windows 7,  tested the cable all again, installed driver again, checked connections again (Cable Midi In for Piano Out and Cable Midi Out out to piano IN)... Didn't work...  So I realised the cable's circuit box was scratched, the painted name was missing a large portion, and I imagined if it was opened before, maybe a technical fix or attempt... I imagine someone "fixed" it once and could had placed the interior wire cables, or soldered, reversed. What else could be the explanation??, I imagined. I believe it would not work but anyway I decided to put the MIDI plugs reversed, intead of the right connection of In>>OUT and OUT>>IN, I placed this time IN>>IN and OUT>>OUT.

      And surprise, It worked !!!  
      MIDI IN LED also blinks now when I play.

      I got the same latency number in pianoteq as before (playing with mouse), 10ms. See no difference, and the response while playing with digital piano.  The cable circuit box switch Advanced Driver (sellect a advanced drive for better performance) instead of a standart one, makes no difference or no difference I can notice in terms of reduce any extra latency the cable have in relation to the software latency.

     Well, it's used but I paid about 23% of what would be a new one. The seller had sent me the money back when I explained every details of instalation and why wasn't working. Now I will contact hin to pay hin again, but will wait the money he sent back get in the credit card account. Should I ask a discount due it only work reversed and the headach I had in these 2 days ??  Háa háaa... I will pay 6% less since now will be out from the selling website, which charges 6% tax for each sale.

It's this model:  https://www.roland.com/global/products/um-1g/

Iy instals, it appears as UM-1G (what should appear accoding Roland) on pianoteq.
When I press the MIDI check button the MIDI out LED blinks, but not the MIDI IN.

It have two swistches, one On Off Advanced Driver, and a One Off MIDI thru. I tried all combinations and did not work.

The cable it's used, but let's hope it's fine.

The seeler accepted to refund if I sent back the cabel. It's from China but the seller it's in my country and have to follow the rules of the site where he selled it.

I need to know about a good brand of MIDI US converter cable that works very well in very old Roland digital pianos.

And this other guy soldered a new ship, missing in a chinese cable, and said some wiering was also wrong, and used MIDI-OX for final fixing:
http://www.arvydas.co.uk/2013/07/cheap- … -required/

Even if you had such a version of the thing, does not worth the effort... ask your money being given back to you, even if you have paid 5$. The seller has to assume responsibility.

Just by any chance, have you tried it with other softwares beside Pianoteq?

I don't personally trust converters of the sort MIDI-USB. Particularly if your Windows initial drivers aren't enough. You can try another or try the card option, you may have better luck. Previously those USB options had latency issues, I don't know if it still is the case.

As for damaging devices by wrongly connecting. If the chip is powered by your PC USB interface, I don't see why it would damage your motherboard if at the other end you wrongly connect it. I may be wrong. As for your digital piano, I'm not sure, but connectors being connected the wrong way isn't something that rare (rule rather than exception). Today even a 100$ music keyboard might be protected against polarity inversions. It may very well be that your seller is accusing you of having done something wrong damaging the converter to absolve him (from having sold you something which never really worked correctly to begin with).