2121 Planar

57F1972.BOO IBM PS/1 Hardware Maintenance Service Manual - Types 2011, 2121
ps1diag2.exe PS/1 Type 2121 Advanced Diagnostics (ZIPed image)

2011/2121 Power

2121 386SX Planar
Video Memory Upgrade

2121 386SX Planar 16 or 20 MHz, 92F9657/92F9672

B1 CR2032 Battery
F1 PS/2 Fuse
J1 Floppy connector (34-pin, power)
J2 Serial/Modem exp. connector (20-pin)
J3 Mouse
J4 Keyboard
J5 Memory exp. connector
J6 Parallel
J7 Audio/Joystick exp. connector (34-pin)
J8 Adapter Card Unit (ACU)/Riser slot
J9 Power card connector (17-pin)
J10 Power/Audio connector
J11 Hard-drive power connector
J12 IDE connector (40-pin)
J13 Fan connector
J14 VGA connector
J15 Hard-drive LED connector
U1 92F9605 02/08/91
U2 N82077AA Floppy Controller
U3 N8042AH MCU PS/2 Controller
U5 92F9623 14/08/91
U6 ?
U7 64F3110 TI CF61533FN
U10 intel 386SX-16 or -20 CPU
U17 84F9287 OKI M7U100-019
U20 84F7985 SVGA
U21,29 RAM solder pads
U22,23,26,27 83F0380 RAM
U24,35 Toshiba TC511665J-80 or BJ-80 RAM (VGA)
U34 84F7986 OKI M7U024-007 IDE?
U36 inmos IMSG171P-35 CLUT
Y1 14.3 MHz? xtal
Y2 10.0000 MHz? osc
Y3 32.768 kHz xtal (RTC)
Y4 25.175 MHz xtal (VGA)
Y5 32.0000 or 40.0000 MHz osc (CPU)
Y6 28.322 MHz xtal (VGA)
Y7 41.5390 MHz? osc (?)

Video Memory Upgrade

The 2121 planar comes with an SVGA video controller, but is only equipped with 256 KB of video RAM. This restricts the adapter to the standard 640x480x16 VGA mode. However the board has a provision for extra 256 KB of video RAM. Positions U21 and U29 can be populated with a pair of Toshiba TC511665J-80/BJ-10 or equivalent 64Kx16 100 ns (or faster) DRAM chips for a total of 512 KB. This unlocks 256 simultaneous colors in the 640x400 and 640x480 APA modes, and it also allows for the 132-column text mode.

Note: Instead of soldering the chips directly on the board I would recommend adding a pair of SOJ40 sockets instead. This method is safer for the RAM chips, and it also allows for much easier part replacement, should the chip(s) be DOA or fail in the future.

The same SVGA controller is also used on the PS/2 Model 25SX planar, and reportedly it's also equivalent to the IBM SVGA Adapter/A controller.

VESA DOS support can be achieved with the VESA.exe driver and supposedly with the IBM SVGA Adapter/A m95svga.exe driver as well.

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