8525 Planar
8086 (8525-001, -004)

Content by William R. Walsh, original here.

PS/2 Model 25 - 8086 "Type 1" Planar
PS/2 Model 25 - 8086 "Type 2" Planar
Riser Card
Graphics Hardware
Upgrades
Floppy Drive


8525-001 has a monochrome ("paper white") display and an 8086 CPU.

8525-004 is the same computing hardware as the 8525-001, only it features a color display. I've seen far more of these with color displays than monochrome ones, so I'm guessing monochrome wasn't as popular of a choice. That seems odd, given the number of standalone PS/2 monochrome monitors I have.


PS/2 Model 25 - 8086 "Type 1" Planar * *

Different version of the planar. Outline not available yet.


PS/2 Model 25 - 8086 "Type 2" Planar * *

25 XT Planar

F1 Keyboard Fuse
J4 Display Connector
J7 Power Connector
J8 4-pin header, 3-pins present.
J9 A/B 30 Pin SIMM sockets
J10 2-pin header (?)
J11 IBM HDD (proprietary)
J12 Floppy Disk Connector
SP1 Speaker
U? Intel 8086-2 CPU at 8MHz
U5 Inmos IMSG171P Video RAMDAC
U6 Hitachi HM53461P
U7 Hitachi HM53461P
U8 Intel P8253-5
U9 72X8203
U10 ROM BIOS (U20?)
U11 Seiko Epson SLA64030J2L
U13 ROM BIOS (U17?)
U14 OKI/IBM 72X8206
U15 Seiko Epson SLA6330J1C
U16 NEC D4164C-10
U17 See U13
U18 NEC D765AC-2 (FDC?)
U19 Siemens 8237A
U27 National Semi. NS8250AV
U33 NEC D4164C-10
U34 NEC D4164C-10
U35 NEC D4164C-10
U38 Sony CXK5864BM-12L
U44 OKI M3764A-15
Y1 14.31818MHz OSC
Y2 25.175MHz OSC
Y3 48.0MHz OSC
ZM1 OKI M3764A-15 (ZM?!)
ZM3 Earphone Connector

Notes:

J8 4-pin header, 3-pins present. (external speaker?)
J11 IBM HDD connector (proprietary, not IDE!)
J12 Floppy Disk Connector (proprietary, runs power over the data cable!)

I've been told that the 4xNEC D4164 are actually the 256KB upgrade that serve to give you a full 640KB of installed RAM. The SIMMs seemingly provide the base memory. (I'm not real sure I agree with that, since the SIMMs would be so much easier to install for an end user.)


Riser Card * * *

Two 8-bit ISA slots. No other components on the riser, aside from a resistor pack.

Outline not available yet.


Graphics Hardware

The 8086 variant of the Model 25 has MCGA graphics hardware, wired to work with an analog VGA monitor. MCGA is a curious mixture of different technologies: in addition to all modes supported by a CGA adapter, it supports the low resolution (320x240) 256 color VGA mode and high resolution (640x480) monochrome VGA. However, EGA display modes are not supported.

All other PS/2 Models having a 286 microprocessor (or better) have VGA graphics hardware at a minimum.


Upgrades

I'm not aware of any for the CPU, short of replacing the entire system board. As far as storage goes, something like an XT-IDE board is probably your best bet. Older IDE and SCSI controllers have their own expansion ROM on board may also work. A standard power connector for a hard disk isn't available, though you can add one. (Use the instructions for the 25SX/30-286/55SX ... the Model 25 8086 does NOT use the same power connector as the Model 30 8086!)

There are two internal expansion slots, both of which are 8-bit ISA types.

Memory expansion is limited to boards that provide additional RAM in compliance with the expanded memory specification (EMS).


Floppy Drive

Floppy drives are the bane of a PS/2 collector's existence. Pretty much all of them still in existence today will require repair before they are usable. At a minimum, you'll need to clean the dust and any foreign objects out of the drive. You might as well plan on replacing every one of the surface mounted electrolytic capacitors on the drive's circuit board, and almost certainly cleaning up the corrosive mess left behind.

Although IBM never sold them configured as such, the 8086 version of the PS/2 Model 25 has undocumented high density diskette drive (1.44MB) support. Not all disk drives will work: only the drives manufactured by Sony seem likely to work correctly. Other drives will only be "seen" as a low density type or may not work at all. The floppy drive controller is an NEC 765 or Intel 8272, both of which support high density diskettes, and the BIOS obviously has some support as well. Whichever planar you have in your Model 25 8086 also factors in -- later models are more flexible in regards to which diskette drives will actually work. (The same is true of the PS/2 Model 30.)


9595 Main Page