DB9 Pinout
IBM Token-Ring RJ-45 STP Adapter cable
IBM Token-Ring UTP cable
   Token Ring - UTP Modular Connector Pinout
IBM RJ-45 STP/D-Shell Conversion Cable
IBM Token Ring Network PC Adapter Cable (STP cable)
IBM Ring In/Ring Out STP Cable
TR Trivia

  Pins 2,4, 7 and 8 are "DC Common" and Pin 3 is +5VDC on most adapters. This DC is used for some few MAUs that need additonal power / adapter present sense signal. Alternatively IBM used "A" instead of "1" and "B" for "2".
   The cable colors refer to the color code IBM used within the ICS (IBM
Cabling System) for all qualified cable types - namely the cable Type-1.

>> So I guess a DB9 to RJ45 connector with the right wiring and a Cat5 cable will not work?

Peter sez:
   But ... (there's always a "but", eh ?) ... but if the length of a single 
workstation cable does not exceed 15 meters I would guess it is safe to cut off the one end from a CAT-5 cable and install a Sub-D 9-pin male plug instead.
   The TR topology allowes to have 100 (200) meter cable length between MAU and station at 16 (4) Mbit/s - and up to 200 (400) meter between RI/RO of two MAUs.
   In this case the cable impedance *is* an important factor - and to stay on
the safe side you should either use IBM Cable type 1 ("the finger-thick hose") or media filters if you use ICS and CAT-5 cabling in a combined setup.
   For a small "home" network with low average traffic and with a small
physical dimension (say: 8 stations, one single 8228 MAU, maximum 30 meters end-to-end) you will most likely *never* run into any problem. 
   But it is unprofessional of course ... ;-)

  This is used when the adapter has a DB9 port, and the MAU used ICS. 

B1 Connector, adapter end 8-position RJ-45 modular jack 
B2 Connector, network end 8-position RJ-45 modular jack or 6 position RJ-11 modular jack 

Token Ring - UTP Modular Connector

ADAPTER END -- NETWORK END      ADAPTER END -- NETWORK END
 RJ-45    to     RJ-45           RJ-45    to     RJ-11

  3 ------------- 3      TD-      3 ------------- 2
  4 ------------- 4      RD+      4 ------------- 3
  5 ------------- 5      RD-      5 ------------- 4
  6 ------------- 6      TD+      6 ------------- 5

1,2,7,8        1,2,7,8        1,2,7,8       1,6 <- Not used

  This cable is used when the adapter is RJ45 (or you use a Media Filter) and the Media Access Unit (MAU) is UTP also. 

C1 Connector, adapter end 8-position RJ-45 modular plug 
C2 Connector, network end 9-position D, male 

  This adapter plugs into the RJ45 port on the adapter and mechanically changes the cable type to STP for use with the IBM ICS cables. 

D1 Connector, adapter end 9-position D, male 
D2 Connector, network end IBM Cabling System Data Connector or equivalent 

  These cables are used with adapters that use a DB9 port. For adapters with RJ45 and DB9 ports, the setup gives you the choice of STP (Shielded Twisted Pair, which is the IBM ICS cabling) or UTP (Unshielded Twisted Pair, or Cat3/Cat5 wiring) 

E1 Connector, MAU end IBM Cabling System Data Connector 
E2 Connector, MAU end IBM Cabling System Data Connector 

 These are true hermaphrodite cables, used to link 8228 MAUs together to form a ring. Each ring adds another 8 data ports to the Token Ring network. I have seen short 1ft, 3ft, and 6ft and longer cables.. 

From Peter
>If I have two MAUs connected RI <-> RO  and there are machines connected to both and then I disconnect the MAUs, can I later reconnect them and get all the machines to see other again? 

   No. Normally not. Depends on if you manage to disconnect the RI/RO cable from both MAUs almost simultanously before the TR adapter(s) connected to them get a "Token Lost" time-out and shut down the ring interface. From the moment you separate the two MAUs one adapter on each becomes "ring monitor", because you have two separate rings at that time. When you reconnect the two rings there are *two* tokens and two active ring monitors in one ring. It takes some time until the negotiation is done which adapter stays ring monitor (or which *other* adapter takes over) and to re-circulate the two concurring tokens on the ring. 

>I have a server connected to one MAU which can't see any machines connected to the other. I don't want to reboot this server. How do I get everything working again properly? 

   If the server cannot see other machines it is a protocol error on the server most likely ... so what's the use to kick of the *other* machines then ? You will need to reboot the server at one point anyway - so why fussing around with the entire ring. 

Question 1: do you see any other station on the entire ring anyway (e.g. Machine A on MAU-1 sees a Machine B on MAU-2) or isn't there any sort of communication across the two MAUs at all ?

Question 2: which protocol are you using ? TCP/IP ? 
I - for example - have a Linux intranet server, that does not show up under "Network Neighborhood" - but the shared ressources (under SAMBA) can be used with NET USE X: \\I-SERVER\I-DRIVE from any station in the network. It is running TCP/IP only, but not IPX/SPX or NETBEUI .... which are required under Winblowz to use the "direct name" ("Find Computer") without having a "hosts" file with the list IP-Adress = Name.