Model 5550 386 Reference & Diagnostic Disk for 5530-S,T/5540-T/5550-S,T,V v1.50 (DOS/V) Reference Disk for 5530-S,T/5540-T/5550-S,T,V v1.50 (DOS/V) Diagnostic Disk for 5530-S,T/5540-T/5550-S,T,V v1.50 (DOS/V) Reference & Diagnostic Disk for 5530/5540/5545/5550/5570 v1.36 (JDOS)

General Information
Video (For S and T models)
Hard Disk interface
   Stage 1 (16/20 MHz) Planar
   Stage 2 (16/20 MHz) Planar
   V0/V1 (25 MHz) Planar
   V2 (25 MHz) Planar
CPU Upgrade
5502 Industrial Computer

PS/55 5550-V24

General Information

Japanese equivalent of PS/2 8570.

5550-S/T, the first Desk Top model of PS/55 line, were introduced to the market in Apr.1988 together with 5570-T (8580 20 MHz analogous). 5550-S/T were similar to the PS/2 Model 70, but IBM Japan modified many aspects of the original design. The most distinctive change is the number of MCA slots. The Japanese 5550-S/T has four MCA slots, compared to 3 of the Model 70. The 4th slot was added for Japanese Display Adapter to handle Japanese characters. For this reason the 5550 planar is a bit wider than that of the PS/2 Model 70, and as a matter of fact, the body is slightly wider as well (see the badge area on the photo below). The other exterior changes are fairly minor - the type & S/N sticker has been relocated below the power switch, and the LED/switch pictograms are slightly different as well. The base of the chassis is made of a sheet metal instead of plastic.

Front view of Model 5550-T (source)

A look inside (Stage 2 T Planar) (source)

The planar of early models S and T had some problem related to the bus mastering feature and those planars were called Stage 1. The later models that were void of this problem were called Stage 2. So there should be 4 types of planars for S and T models and another one (or two) for 25 MHz version.

Easy way to identify Stage 1 and Stage 2:
   If the Power SW lever is RED, most possibly it's Stage 1.
   If the Power SW lever is WHITE, maybe it's Stage 2.

Identifying with serial numbers.
Even if the Power SW is white, systems with following serial numbers belongs to Stage I:
   5551-S09 S/N before 97-19300
   5551-T09 S/N before 97-44700
   5551-T0A S/N before 97-58000
   5551-T0B S/N before 97-93100

Brief Chart of 5550 and Industrial 5500 models based on PS/55 System Guide
O: means the model is listed in the Guide Book
+ UG: means 486DX upgrade option is also listed

5550 5502
-S -T -V0 -V1 -V2 -S/T -TG -V2 -VG
'88-07 O O
'88-12 O O
'89-06 O O O
'90-02 O O O + UG O
'90-07 S1 O T1 O O + UG O
'90-11 S1 O T1 O O + UG O S1/T1 O O
'91-05 S1 O T1 O O O S1/T1 O O
'92-02 O O S1/T1 O O + UG

Most possibly switch over to Stage II from Stage I was made around May to Jul 1990.
As for 5530, 5530-T04/T08 (Stage II) and 5530-S12/S14 (ZSX on Stage II) were listed in Nov 1990 edition.

5551 386 Series Lineup (-S/T/V, original HERE)

Model CPU Memory
HDD Video
5551-S09/S19/S0A/S1A 80386DX 16 MHz 2/16MB 30-60MB PS/55 DA
5551-T09/T19/T0A/T1A/T0B/T1B 80386DX 20 MHz 2/16MB 30-120MB PS/55 DA
5551-V0A/V1A/V1B/V0B 80386DX 25 MHz
64KB L2 cache
4/16MB 60-120MB PS/55 DA
5551-V24/V28/V2B 80386DX 25 MHz
64KB L2 cache
4/16MB 40-160MB PS/55 DA


Ref. Ver. 1.00 to Ver.1.36 are based on JDOS.
Ref. Ver higher than 1.4x are based on DOS/V.
Ver. 1.50 covers most of of all 386 models such as 5550-S/T/V, 5570-T/V, 5540-T, 5530-T.


For S, T and Vo/V1 models

As like as PS/2 8570, PS/55 5550-S/T have VGA chip on the planar. But in order to handle true Japanese fonts, PS/55 Japanese Display Adapter II (with AVEC connector) is equipped with earlier models of 5550-S/T (and 5570-T). VGA port on the planar is covered with a plastic plug.

For V2 model

I'm not sure about a display adapter used for this model. V2 planar does not have a VGA chip and it has BVE MCA slot. Then most possibly Display Adapter B or B-2 might be equipped with V2 model.


Double-decked shape. Only one module can be used.
This module should be installed at J9( memory slot #3)
23F21654MB5550-V0/V1. Double-decked ?
79F25364MB5550-V, 5541-T, 5530-S/T, 5510-T
79F25008MB5550-V, 5541-T, 5510-T

Hard Disk Interface

Same as 8570, ESDI (roughly speaking).


There were various types of planar for 386-class 5550.

Model CPU Planar Level MCA Slots
S 16 MHz Stage 1 & Stage 2 4 Slots
T 20 MHz Stage 1 & Stage 2 4 Slots
V0/V1 25 MHz not sure, most possibly 4
V2 25 MHz 5 slots, No VGA chip on the planar

I've once heard that S stands for Sixteen, T stands for Twenty and V stands for twenty fiVe.

Stage 1 Planar (16/20 MHz) (also used by IBM 7561/7562)

Following outline is a Stage 1 T planar. Don't know how it differs from Stage 1 S planar. But most possibly these might be same except OSC Y5.
Following Stage 1 20 MHz planar looks like 8570 Type 1 planar.

20 MHz T Planar P/N 65X1377, EC 341537S

F1 1A KB/mouse fuse
J1 Unknown
J2 Pads
J3 Mouse port
J4 Keyboard port
J5 Battery/Speaker header
J6 HDD15 video connector
J8 Hard-drive/Floppy riser
J9,15 16-bit MCA slot w/ AVE
J10,11 32-bit MCA slot
J13 MEM Location 1
J12 MEM Location 2
J14 MEM Location 3
J16 4 pads only
J18 3-pin header, unknown
J21 Parallel port
J22 DB25 serial port
U1 LM340 VR
U8 NEC D72065L
U13 72X8299 PIO
U16 P8042AH
U28,38 8259A-2
U30 94X1265
U37 Motorola MC14069UB
U39 Motorola MC146818AFN
U69 Sanyo LC3517RM
U111 65X1506 BIOS Even
   M5M4464AL 64Kx4 DRAM (video)
U115 90X8941 VGA
U128 65X1507 BIOS Odd
U154 80386-20
U159 80387 Math co-pro
U160 90X8134 DMA Controller
Y1 32 KHz xtal
Y2 25.175 MHz osc
Y3 1.8432 MHz osc
Y4 28.322 MHz osc
Y5 40.0000 MHz osc
Y6 32.0000 MHz osc
Y7 14.318 MHz osc

U111/128 BIOS Even/Odd, 2x27512 EPROM
   PS/55 Model 5550: 23F3012/23F3013
   IBM 7562: 65X1506/65X1507

Stage 2 Planar (16/20 MHz)

Recently I had a chance to see Stage 2 20 MHz planar and noticed it is totally same with my Stage 2 16 MHz planar except installed OSC Y1 and planar P/N.

  1. Aside from the fact that 5550 has 4 MCA SLOT, Layout of Stage 2 planar is different from that of 8570 in following points.
  2. 5550 Stage 2 planar has only one SIMM socket on the planar. another 2 sockets are placed on the Expansion card which is connected to the planar through J3.
  3. Bus riser J7 is moved left (moved downward in the outline below), hence HDD/FDD riser is different from Stage 1 model and that of 8570 Type 1)
  4. Speaker/Battery connector is not a riser type. SP/BT ASM is connected through wire and a male plug like 8580.
  5. ZIP VRAMs are directly mounted on the planar.

See the diagram below and compare it with the PS/2 8570 Type 1 planar.

Stage 2 planar P/N 38F6776 (S - 16 MHz), 54G1612 (T - 20 MHz)

J1 Power connector edge card
J2 Keyboard port
J3 Memory exp. connector
J4 Mouse port
J6 Parallel port
J7 Floppy/Hard-drive Riser
J8 DB25 serial port
J9 HDD15 video connector
J10,11 32-bit MCA slot
J13,15 16-bit MCA slot w/ AVE
J14 Speaker/Battery connector
U10 NEC 72065L
U20 33F8602 FDC
U22 33F5946 CPU GA
U23 33F5944 Memory Ctrl. GA
U31 33F5938 I/O Ctrl. GA
U32 38F6972 EPP3 GA
U38 N8042A/90X9298
U43,44,52-57 M5M446AM-12 VRAM
U51 LM339
U61 57X4211
U62 90X8134 DMA Controller
U64 90X8941 VGA
U74 80386DX-16
U83 Math co-pro socket
U84 MC146818
Y1 32 MHz (S), 40 MHz (T)

System Memory Expansion Card For 5550-S/T Stage 2 Planar (P/N 38F6776)

J1 102P planar connector
J2 MEM 3 (2MB/4MB memory slot)
J3 MEM 2 (2MB memory slot)
U1 LS244 (SN74LS244N)

V0/V1 (25 MHz) Planar

Outline not available.

V2 (25 MHz) Planar

As a matter of fact, I have not actually examined complete V systems ever. I just have a V2 planar. When I draw outline of the planar, I noticed that 25 MHz V2 planar doesn't have onboard VGA. Man, this planar has 5 MCA slots and, to my surprise, there are solder pads for another 16-bit slots!
Bus riser slot J6 is shifted to the left comparing S planar I have. It means there should be more than three types of Bus Riser Card. Locations of bus riser connectors are different with each other.

25 MHz V2 planar P/N 79F5325, EC C27264D

BIOS P/N 79F2757
DL2 TQW-100
J1 Power connector edge card
J2 Mouse port
J3 CPU Daughtercard Connector
J4 Keyboard port
J5 Parallel port
J6 Bus riser (watch the location)
J7 DB25 serial port
J8 Memory slot #2
J9 Memory slot #3
J10 Pads for 16-bit MCA slot
J11 Memory slot #1
J12 16-bit MCA slot
J13,15 32-bit MCA slot
J14 32-bit MCA slot w/ BVE
J17 32-bit MCA slot w/ AVE
J16 Speaker connector
U14 90X8134 DMA Controller
U15 N8042 (90X9298)
U41 56F7502 ISERE
U46 72X8299 PIO
U66 57X4311
U73 NEC D72560L
U77 NS 16550
Y1 32.0 MHz
Y2 14.3 MHz
Y3 40.0 MHz
Y4 1.8432 MHz

CPU Daughter Board

Main differences between 8570 sub board and 5550-V2 sub-board are:

  1. Pin orientation of 387 co-pro
  2. Planar-daughter board connector

From 5550-V2 system guide;
One 4MB SIMM was originally installed, expandable up to 16MB on the planar.
Option SIMM's are:
1) 4MB P/N 79F2536
2) 8MB P/N 79F2500 (only one module can be used on a planar)

A guy once reported that he had changed 50 MHz osc to 60 MHz and system worked without POST error.

Riser card for HD and FDD

As written in V planar section, there are several types of bus riser cards. I once had two types of riser card but there should be three or more.

CPU upgrade

I tested following upgrade kits on my S and T models.

  1. Evergreen upgrade modules with IBM486BL2 and BL3.
    Cyrix and TI chips could be used on S/T models but not on V models due to 64K L2 cache on the CPU board (I have not examined).
  2. Kingston MC master 486 (originally made by AOX).
    I used it on T planar. MCMaster can take a 5x85 CPU but you can't use neighboring MCA slot in order to use 5x86 CPU with a heatsink. Not a good choice for 8570 because it has only 3 MCA slots.
  3. PowerBoard
    In order to use a PowerBoard on S (Stage II) model, some adjustment is needed to place the board properly.
    1. Need to adjust location of metal parts for screw holes to keep the planar.
      Location of screw holes at left front edge is different between S and T/V.
    2. a Bus Riser card for FDD and ESDI hard disk for T model.
    3. battery and SP unit for T model.

Genuine option by IBM 80486 25 MHz Processor Upgrade Kit (P/N 57F0085) was listed for 5551-V0x model.

5502 Industrial Computer

5502 is an industrial model number.
Industrial models are numbered as " 5500" and each model has unique number such as 5502-S1x, -T1x and so on.

Type CPU
Option Slot
S01 16 MHz
16MB -
S11 16 MHz
16MB -
T19 20 MHz
16MB 30MB
T1A 20 MHz
16MB 60MB
T1B 20 MHz
16MB 120MB
TFx 20 MHz
Poss same with TGx
TGA 20 MHz
16MB 60MB
4 *
TGB 20 MHz
16MB 120MB
4 *
V2A 25 MHz
16MB 80MB
2 (half)
V2B 25 MHz
16MB 160MB
2 (half)
VGA 25 MHz
16MB 80MB
VGB 25 MHz
16MB 160MB

Number of Option Slots

System Guide describes number of Option Slots left for users except already occupied with a Display Adapter. So basically, one slot should be added to the number shown in a diagram.
Model S11 to T1B meet with the rule and one 16-bit AVE slot might already be occupied with a display adapter. Then how it comes that TGA and TGB were noted as 4 + 1? Wonder if these 2 models were not shipped with any Display adapters and use VGA on the planar?
Next question; it seems models Vxx models DO have activated 6th 16-bit slot shown in outline of 5550-V2 planar. 5550-V2 planar has four 32/16-bit slots including x1 AVE and x1 BVE slot. But above diagram shows 5500-V have three 32/16-bit slots and two 16-bit slots. If 32/16-bit BVE slot was occupied with a Display adapter, total MCA slots would be SIX including two 16-bit slots. Would like to see the planar.

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Ardent Tool of Capitalism - MAD Edition! is maintained by Tomáš Slavotínek.
Last update: 30 Jul 2023 - Changelog | Legal Info & Contact