Reference Disk for Type 4-
Diagnostics for Type 4- (Common to all complexes)

Memory
Min/Max on system board: 8/64MB Parity, 8/256MB ECC
RAM: DRAM (PS/2 72-pin SIMM, ECC or Parity) 70ns
ROM: 128kb 
Cache: 8kb L1, 256kb L2 (P60, P66, P90)
*  SynchroStream^TM
* 40 MB per second streaming data transfer.
* Error Checking and Correcting (ECC) memory controller
* 256KB Level 2 memory cache (write-through) on Pentium complexes, 128K on DX2-66
* 20 MHz DMA; 32 bit DMA can directly address all memory
* DMA supports Subsystem Control Block.
* Faster bus arbitration (than Base 1) for busmaster performance.
* Enhanced Dual Path Memory
* Subsystem Control Block enabled
* Vital Product Data support.
* Synchronous Channel Check support
* Data bus parity support
* A logging facility is provided (for ECC or system errors)..

BIOS Releases
Trying to flash BIOS 5 and up from 03 or Lower
Complex BIOS Levels
FDIV Processor Replacement

Pentium® processor Replacement (FDIV) Information 
  If you have a -xPx or -xQx complex (even the mighty -xPx), chances are it has the FDIV bug. Intel will swap out your processor with a like processor. Same speed. No upgrade for the FDIV chip is available. Read the stuff on this link. It will give you the phone# and the requirements for swapping the chip out (Includes the CPUID program to identify the presence of the FDIV bug). You will have to give them a credit card number.
   They will send out a non-FDIV chip and a pre-paid shipping envelope. You pop the old chip out and return it to Intel. If they do not receive the old chip within 30 days they will charge the credit card number.
  I had my replacement in under a week of my call....

Diagnostic LEDs (Extrapolated from the Type 3 information)
   The Type 4 processor board  has two LEDs; one in position CR1, and one in CR2. 

Serial Data Link

The vaunted P90 complex

J3- Serial port connector to operator panel board.
J5- The "Flash ROM bank" switch -by the way- was originally planned for a sort of "emergency mode". Once you screwed up the Flash-BIOS you could toggle the bank, insert any working flash update in the FDD A: and restart the  machine, which takes the flash-image from the floppy drive and recovers (as it can be done on the 704 in the "Bios recovery mode"). However: the base boot-BIOS did not have the required routines to delete the loused up bank of the Flash-ROM ... and as far as I know the loading of an image from Floppy  does not work. Another useless feature. 
J6- Known but to God. Shocking news! This jumper has been reported on a P66 complex!!
Artifact- Serial Link J5 on Type 4 complexes  (-xNx, -xPx, -xQx, -xYx)
     The serial link was (as far as I know) intended for the use with an earlier system management adapter, which didn't made it to the salesroom. The idea was to supply a sort of status-link to the processorboard and the   SCSI- adapter(s) and the (possible) backplanes on the later servers. 
Cache controller  Try HERE and search for A82497-60. Thanks, Senum!
CR1 and CR2 Diagnostic LEDs. 

 There are two FRUs for the P90 complex-

 If you go to the EPRM it says:
 (wrong Pentium® 90MHz Processor Card !) 06H3739
 Pentium® 90MHz Processor Card                 06H7095

Oliver Schweizer said 
   I once called the spare part hot line and they told me that the 06H7095 is intended just as a replacement for a crashed complex. According to them the number change came because the original complex could contain the bug-ish P90 and the replacement unit not. If I remember correctly they asked about 1500-2000 $ for the 06H3739!! A real tempting offer ;), but after weeks of sleepless nights I decided to stick with my type 2 complex (and got the pentium power now for about 5% of that price).