Folks, this is it. The much sought after Reply Corporation upgrade planar for the IBM PS/2 Model 25 and Model 25-286 systems. This board gives you the most performance you can cram into a Model 25, with up to an Intel 486DX4 100MHz CPU. There is nothing higher.*
Thanks to Bob Watts for putting one up for sale complete with manual and all installation parts. I never, ever, thought I would find one.
* Well, almost. A company by the name of PC Enterprises marketed a board known as the Genesis\PC. It's a totally different board than the Reply board. In fact, it is a lot more "clone like" with regards to the BIOS and chipset, but it has a lot more of the "original" PS/2 features, like an earphone plug. There's even a place for a game port and a COM2 port.
Content by William R. Walsh (original HERE). Modified by Major Tom.
Model 25 Reply PowerBoard
J1 Cyrix CPU select pins
J2 Intel/AMD CPU select pins
J3 VGA IRQ Jumper
J4 Monitor connector
J5 Hard disk power connector
J6 CMOS RTC Battery Connector
J11* ISA bus riser connector
J12* FDC mode selector
J13 IDE connector
J14 Power supply connector
J15 Floppy Disk Drive connector
J16 Power supply connector
J18 CMOS Clear jumper
J19 IBM "ST-506" hard disk connection
Y1 14.318MHz OSC
Y2 ? OSC
U3 NEC 42S4260-70 VRAM
U4 Empty pads for another VRAM
U5 Lattice GAL 20V8B
U6 Cirrus Logic GD5429
U13 486 Socket (auto 5/3.3 V, no POD)
U21 SMC FDC37C661QF P I/O controller
U22 VLSI VL82C483FC3
U27 VLSI VL82C114FC1
U30, U33 CSI CAT28F010N-15 (BIOS?)
U35 PLCC labeled "02-1420023F3"
Q2 Linear Tech LT1085 VRM
U28, U29 SIMM sockets
* not marked
J1 Cyrix 486 CPU select (put jumpers on all pins)
J2 Intel or AMD 486 CPU select (put jumpers on all pins)
J3 VGA IRQ (1-2 Disabled, 2-3 Enabled)
J18 CMOS Clear (1-2 Normal Operation, 2-3 Clear)
I'd highly advise getting the manual at the very least to perform the Reply upgrade planar installation. Having all of the items needed to do the upgrade is not really required--all you really absolutely need is the planar, floppy disk cabling and the riser. A floppy "cable converter" is included with a "new" Reply board, but I didn't have to use it in any of the install scenarios I tried.
I will at some point, though probably not soon, be publishing a guide to installing the Reply board, as well as the PC Enterprises Genesis board.
Upgrading (Video and CPU Upgrade Thoughts)
I have two known attempts to use non-Intel upgrade CPUs on the the Reply Model 25 Powerboard. The first attempt (using a Kingston TurboChip) by David Beem did not succeed. The planar wouldn't even do POST.
The planar doesn't have a POD style 486 socket, so using a Pentium Overdrive chip is not an option. It looks as though the planar tops out at 100MHz, but even then that's a big improvement from whatever your Model 25 had beforehand.
My own attempt with an IBM 5x86 CPU at 100MHz--the system powered up and would display the BIOS copyright, but it froze after that. I suppose that possible CPUID difficulties are the cause of David and I's trouble with non-Intel CPUs.
Purpose of U4? It's a place you can put additional VRAM. Reply seems to have done this on all their boards--they have left this set of pads empty. I would think another 512K VRAM chip at this location would give you a nice 1MB of VRAM, enough to run high color modes with, but nothing beyond 640x480 at 60Hz!!!