PC720 6860

Introduction
Models
Planar
CPU
Jumpers
Memory
Video
Hard Drive Interface
CD-ROM
L2 Cache
Small PCI
Riser Card
PCMCIA
PSU
Service Partition


Introduction

PC720 6860 was introduced to the market together with PC750 6886 in 1995. 6860 is not a Pentium based PC. IBM Japan didn't introduce PC730 6876 in Japan, instead they made this unique space-saving desktop model. PC720 6860 is a strange *hybrid* PC with one MCA slot, one shared MCA/PCI slot, and a ISA-like slot for PCMCIA /A exclusively designed for this box.


Models

PC720 6860
J4G
J00
J04
J08
JZG
CPU
iDX4-100
i486DX2-66
L2 Cache
128KB
None (Socket is omitted)
RAM (std/max)
8MB (Max 128MB, 32MB x4)
4MB (128)
VRAM
2MB
1MB (Upgradable to 2MB)
FDD
3-Mode (1.44MB/1.2MB/720KB) x1
HDD
728MB
540MB
Video
S3 Vision864
PS/55 D/A NI
Option Slot
PCI or MCA x1, MCA x1
MCA x2
Small PCI NIC
TokenRing Ethernet
PC Card Slot
Type I/II x2 or Type III x1 (ISA style PCMCIA /A)
Dimension (mm)
360 (W) x 370 (D) x 89 (H), 9 kg
Pre-installed OS
PC DOS J6.3/V, Windows J3.1
DOS J5.02Z

Type JZG was equipped with a PS/55 Display Adapter /NI-J and DOS J5.02Z (JDOS).
Model 6869 is an ISA version of PC720.
Model 6863 (also ISA) is named as "PC720" but it's a Pentium machine with P-100.
6863 uses same planar with PC750 model 6883 (probably sold only in Japan, planar is different from that of 6885/6886 or 6887).


6860/6869 Planar (DX4-100 model)

J1 FDD Connector
J2 IR/PCMCIA
J5 Power Switch
J11 PSU
J12 PSU
J14 CPU Select (SX/DX)
J19 Unknown (Default 1-2 closed)
J20 PSU (Power Good?)
J22 FAN (Solder pads only)
J23 L2 Cache socket (DX4 models only)
J24 Riser Slot
J26 PCI-1 (connector for Small PCI)
J27 PCI-2 (solder pads only)
J32 Speaker
J34 Volume
J36 Suspend/Resume
J37 Power & HDD LEDs
J44 VESA Video
J50 Frequency select (66/50 MHz)
J51 Mouse EN/Disable
J52 FDD write EN/Disable
J53 Clear CMOS (1-2: Normal, 2-3: Clear)
J54 Password Overwrite
J55 CPU Voltage select (5V/3.3V)
U7 Socket 3
U16 S9424BP/PC87323VULB
U18 M33s0570-013 OKI/06H3669 IBM
U24 85G7319
U40 Unknown
U42 Unknown
U41 S3 Vision864/86C864P4
U53 S3 SDAC/86C716MG
U55/U56 Sockets for Additional VRAM
U57/U60 DRAM KM416C22568J-6

J2 is silk screened as "IR/PCMCIA". It's obvious that PCMCIA is meant for a 2nd PCMCIA device which could be installed at the front end. I've believed for a long time that IBM only planned to develop such a device, and that they never made it. That was until I got my 6869-J4K (ISA DX4-100 model which is not listed in my PC Guide Book). J4K has additional PCMCIA slot just below the FDD bay which you can see in the picture at the top of this page. And what does "IR" mean? It's likely for some sort of IrDA device. No clue if it was ever released for the PC720.

CPU

Planar can take a DX2-66, DX4-100 or PODP5V83. No interposer required to use 3.3V CPU's. In order to use PODP, BIOS should be updated to KOJT66JP. See below.

PODP (& Win95)

The PODP Support Diskettes Kit consists of 3 parts:

  1. 6860ref.lzh Reference Diskette Ver. 1.10
  2. 6860diag.lzh Diagnostic Diskette Ver 1.11
  3. PC720SP.lzh System ROM update utility Ver. 1.10A (KOJT66JP)

Note:
   Win95 support program, win95serv0.exe (dead), is not for 6860 but for 6863/6869 and other ISA models. 32bit PCMCIA driver contained in this archived file is not usable on 6860. It's for 6863/6869 (and it may be for Win95A).

Jumpers

J55 - Voltage select

For 5V CPU close 2x3 jumper blocks near to the PSU connector.
For 3.3V CPU close 2x3 jumper blocks near to the CPU socket.

J14 - CPU select

For 486DX set jumper to position 2-3 (default).
For 486SX set jumper to position 1-2.

Other Jumper Blocks

J19 - purpose unknown. Default is 1-2 closed.
J50 - Output frequency select for programmable IC? (huh?) 1-2: 50, 2-3: 60.
J51-J54 - Default setting for these jumpers are all 1-2 closed.

Memory

The planar has 4 SIMM slots and takes 4, 8, 16, or 32 MB, 70 ns, FP, parity modules.

Video

S3 Vision 864 1MB (2MB for J4G model). Win95 recognize the chip with it's built-in driver.

JZG model doesn't use onboard S3 Vision but use a PS/55 DBCS Display Adapter/NI-J together with pre-installed DOS J5.02/Z (specialized DOS J5.02 for this model).

Hard Drive Interface

Only one IDE channel is provided. There are solder pads for 2nd IDE channel on the planar, but even if the 2nd channel could be activated, there is no room for 3rd IDE drive.
The drive interface is EIDE and it can handle drives larger than 524 MB. I've used a 2.4 GB drive, and a 6.4 GB Seagate drive with 15 heads. Both worked well. I've also tried a 8 GB Seagate drive, but it wouldn't detect it.

Hard drive runs in MS-DOS Compatibility Mode Under Win95

Win95 will load "standard IDE/ESDI hard disk controller" with configuration #1 which has IRQ value fixed to 15. Change the configuration to #0 which has IRQ 14, all drives will work properly.

CD-ROM

A genuine optional 2x speed CD-ROM (you can see it in the picture at the top of this page) is # 85G7285. I have a 4x slim drive for Toshiba laptops.

L2 Cache

Same socket as in 9577i or 9585 is used. L2 cache module is P/N 85G4865 "128KB L2 Super Cache". This module can be used for M70/80 PowerBoard. To say the truce I bought my 1st 6860 in order to get a cache module in it. The DX2-66 model does not have the cache socket.

Small PCI

I've never seen this type of connector in any other PC. IBM Japan made only 2 adapters for this interface:

  1. SFF PCI Ethernet card, C/R 85G4854, equipped in 6860-J08
  2. SFF PCI TokenRing card, C/R?, equipped in 6860-J04. I want to see it!

Riser Card

   All models other than JZG use same Riser Card which has PCI/MCA shared slot x1, MCA slot x1 and one ISA style slot for 2Slot PCMCIA/A (P/N 54G0547). Riser Card for JZG doesn't have a PCI slot but it has one more MCA bus slot for PS/55 Display Adapter /J which locates under connector J6 (opposite side of PCI slot J5). I'm not sure but probably J1 is for Enable/Disable selector for PS/55 display adapter. Outline below is the one for models other than -JZG.

J1 Video /A selector ? default 1-2 closed
J2 Battery connector (CR2032)
J3 MCA1
J5 PCI
J4 MCA2
J6 ISA Style slot for PCMCIA /A
J9 PSU
U1 74F760D
U2/U3 F543
U4 F245
U6 06H5423 (blue translucent chip)
U8 10G7808
U15 M91S028AT OKI/06H6468
U16 06H4542
U17 LH5168N-10L

PCMCIA

2 slot PCMCIA /A with ISA style connector is equipped in all models. ISA models (6869 and 6883) also use same adapter. Win95 built in driver can't handle this adapter properly on MCA models but the very same adapter installed in ISA models can be used without any problem under Win95B or Win98.
I tested a driver for Win3.1 "PC Card Director" on my 6860-J4G and I found it could handle modem card. I've been using a 28.8Kb Double Jack Modem Card under Win95B. PCMCIA device is not seen under Device Manager, but the card securely detected in PC Card Director. I don't know if other cards such as NICs or SCSI PCMCIA can be used.

PSU

Max. power consumption: 70W
Regular power consumption: 40W

6860 has a very unique PSU. The cooling fan will slow down if the total system power is lower than 50W, and will stop to spinning completely if bellow 30W. Thus the cooling fan usually stays idle. When I got the 6860 I've immediately noticed that the fan wasn't running at all. As I didn't know about this unique feature I thought there must be some fault on the circuit board of the PSU. I disassembled PSU and soldered 12V line directly to the fan assembly. Only latter on have I learned about this unique function. The jumper wire is still there... Some machines have input AC voltage selector. Mine has a "fan mode selector", summer mode with direct connection and winter mode with original connection.

Mine works fine under DOS. But under Win95B it usually freeze at start up after the Win95 logo appears on the screen. I solved this symptom by modifying MSDOS.SYS to have a start up menu with default boot for Win95 after 60 seconds of delay time to boot. Maybe mine needs some delay for stable DC output for planar, a hard drive and a CD-ROM. I'm sure that this symptom is not related to the above mentioned fan cable modification, 'cause I have the same problem even when I switch back to the original cable connection.


Service Partition

6860 is not an IML machine, but it does support service partition (reference partition?).
My 6860 takes long time till the "Set Configuration" page comes on the screen when I boot the system with the Reference Diskette. It stays quiet while it reads configuration files as if the system froze. But from service partition stored on the hard drive it goes straight into configuration menu.


PS/55 Index