Model 25 Reply PowerBoard
"The Final Frontier*"

Content by William R. Walsh, original here.


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.


Model 25 Reply PowerBoard

Reply PowerBoard Outline

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
J10 Pads
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)


Thoughts

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.

Reply Planar Parts


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!!!


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