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Content by Jim Shorney © 2003 (archived original). Edited by Major Tom.
Intro
This page details Jim's attempts to upgrade the IBM 8573 P70 to get the most
out of this neat little PS/2 portable computer. It also includes information
on the P75.
P70 Information
The IBM P70 is a PS/2 Micro Channel portable, often called "luggable", 386
computer. It had no batteries, which required you to lug a power cord along
with it wherever you went. It was a fairly sophisticated machine, having more
in common with a high-end server than with other luggables of it's day. It came
in 386DX-16 and -20 MHz speeds, with 30 MB, 60 MB, or 120 MB DBA-ESDI hard disk
options. The display is a gas-plasma type, which means basically that it is an
incredibly complex neon lamp. This makes it one of the few modern computers
that can be said to actually contain a vacuum tube! The display/controller
combination supports standard VGA resolution at 640x480 pixels (16 gray
levels), and includes a 15-pin connector on the rear panel for an external VGA
color monitor (16 colors supported). CGA and EGA resolutions are also
supported. A maximum of 8 MB of RAM is supported on the system planar, with an
additional 8 MB on a memory expansion card in one of the two Micro Channel
slots. One 16-bit and one 32-bit Micro Channel expansion slots are provided,
along with a socket for a 387DX math coprocessor. Other features include a PS/2
mouse port, serial port, parallel port, internal 1.44 MB floppy disk drive, and
an external floppy disk drive port. All of this snaps together in a neat little
package about the size of your average briefcase - a lot of technology in a
small area in it's day!
The P70 came in two planar versions: the
older 38F4688/65X1564, used
primarily in the 20 MHz -061 machines (but also seen in some -121 20 MHz
boxes), and the newer
38F6973/56F9085 used in 16 MHz and 20 MHz -121 models. The 38F4688/65X1564
planars have the 386DX socket immediately to the right of the 387DX
coprocesssor socket, and two BIOS ROMs near the upper edge of the board. The
38F6973/56F9085 has the 386DX socket above and to the left of the 387DX
socket.
Another distinguishing feature of the newer models is the inclusion of video
output filtering on the video card instead of on a 'daughter card' fitted in
series with the video output cable. The newer planar seems slightly
faster on some benchmarks, but the difference is hardly noteworthy.
| 8573-031 |
30 MB Hard Disk, 16 MHz planar |
| 8573-061 |
60 MB Hard Disk, 20 MHz planar |
| 8573-121 |
120 MB Hard Disk, 20 MHz planar |
P70 Model Number Breakdown
Floppy Drive Removal & Replacement (P70 and P75)
I've been getting a few questions on this lately, so here it is.
There are two mounting methods, referred to as H1 and H2 in IBM documentation.
H1 was mainly used in the P75, but I have also seen it in the P70.
Louis Ohland has H1 removal instructions here.
Detailed H2 removal can be found here.
For the H2 version, remove the plastic housing, starting at the left
side. Then remove the large screw that will be visible as you peek
in below the bottom edge of the drive where the cable plugs in (use a flashlight).
The frame will then slide up and out.
Blow the dust out of the drive and run a cleaning diskette through it
before giving up on it completely; sometimes this is all it takes to get
them operational. Check Bob Eager's comment
HERE about
replacement drive part numbers and sources.
Note: If the machine is unconfigured (dead
CMOS battery), it will ONLY boot from
a reference disk or a DOS boot disk that has been tricked up with Bob Eager's
REFSTAMP utility. Boot from the internal
hard drive will not be possible until the machine has been configured.
'Unidentified Card in Slot x' Error during System Configuration
If you have just replaced the CMOS battery, or installed a new card,
you may get this error. There is nothing wrong with the computer
or the option card. This is easy to fix; you will need the reference
disk and the option disks for any option cards you have in the machine
(usually available for download from the card manufacturer). If the
option disk is not available, you can probably find the required ADF files
on Peter
Wendt's web site. Follow his downloading instructions carefully,
and copy the file(s) to a blank diskette.
Next, power the machine up and boot on the reference disk. If the machine
wants to run 'Automatic Configuration', say NO at this point. Select 'Copy an
Option Diskette' from the first menu, and follow the directions on the screen.
This will copy the option files to your reference disk, and the error message
will not appear the next time you run the configuration.
P70 Upgrade Paths
Memory
According to IBM, 16 MB is it. End of story. The planar supports a maximum
of 8 MB, using four 2 MB 72-pin SIMMs with
Presence Detection. You can
have another 8 MB on a RAM card. But as we all know, there are often
workarounds. One excellent workaround is to use one of the Kingston/AOX
MCMaster upgrade boards. This is perhaps
the best option for many people, as it also gives you a processor upgrade with
the associated architecture and chipsets to get the most out of it (more on
this later). The MCMaster 486 models support up to 64 MB in a 32-bit MCA slot,
and have two 72-pin SIMM sockets. Later versions, flashed with the most recent
BIOS, support non-parity SIMMs. Although the installation guide shows 16 MB as
a legal combination, when I installed two 8 MB SIMM modules in mine it would
not recognize the full 16 MB. One 8 MB and one 4 MB module worked fine, as does
the 8 MB module alongside an IBM 92G7322 16 MB 60 ns non-parity module. The
computer runs quite nicely with 24 MB of RAM! Louis Ohland had this to
contribute on the subject of 8 MB SIMMs:
I had tried two 8MB non IBM SIMMs on an MCMaster. No matter what jumper
settings I tried, or swapping SIMMs, it would only recognize one SIMM.
Put in some SIMMs from an 8595, and it saw both....
It would seem that the MCMaster doesn't support clone-type dual-RAS
(double-sided) 8 MB SIMMs in both sockets at the same time. Other combinations
should be possible with single-RAS chips; anyone who has information, please
send it to me for inclusion here and I will give appropriate credit.
It may be necessary, with faster than 33 MHz CPU's, to set the MCMaster to
"Report MCMaster Only" memory, as the planar memory may not be able to keep up
and lockups will result. In fact, if you are running an advanced operating
system like Linux, Window 9x/NT, or OS/2, you will want to set the MCMaster up
to use only it's own onboard memory. The reason for this is the MCMaster has to
access the planar memory over the MCA bus; this is much slower than accessing
the onboard memory, and will result in a significant performance penalty when
using a "flat memory model" 32-bit operating system. I found this out one time
when I put an ISA RAM card in a fast 486 clone; OS/2 adjusted itself to run at
the speed of the slowest memory in the system. It wasn't a pretty sight. More
RAM is not necessarily better.
The MCMaster utility diskette can be found
HERE. More information on the MCMaster can be found
on Fred Spencer's 8580 Processor Upgrade page.
Other memory cards should be able to break the 16 MB barrier with the
"stock" 386 P70, as has been documented HERE
(subject to the same limitations). The main disadvantage
to this approach is that you need to use a 32-bit memory card, which takes
up your one-and-only 32-bit MCA slot. This prohibits using an IBM
SCSI adapter or long-card network adapter in the computer. One potential
RAM card is the Microram 386 (941366, Rexon/Tecmar Inc.). Other possibilities
may be the "enhanced" cards from Kingston, Acculogic, and IBM, among others.
If anyone has successfully done this, I would appreciate hearing from you.
Processor
IBM did not intend the P70 processor to be upgradable, as far as I have been
able to find out. It's possible that one of the IBM upgrades for the Model
70/80 may work, but every one that I have seen has not been usable due to the
orientation of the CPU socket in the P70. An IBM upgrade for the 5530 (if such
exists) may fit the -031/-121 planar, however. Anyone having more definite
info, please let me know.
Various aftermarket plug-in 386-to-486 CPU-only upgrades should work. I had
a Cyrix 386/486 CPU installed for a while, that is pin-compatible with the
386DX. It worked fine, although the P70 BIOS did not support the write-back L1
cache in the CPU. DON'T enable write-back if you try this, or you WILL
experience hard drive corruption! The increase in performance is nothing to
write home about, but if you just need to add a little speed, it's the most
economical way to go. You do need software from Cyrix to enable the internal L1
cache, though. I will be publishing comparative benchmarks here when I get time
to take some data.
Kingston offered two types of
486 Now! CPU upgrades (in SX and DX versions) for the P70:
486/33PD3-P70 (DX) and
486/33PS3-P70 (SX) for the 38F4688/65X1564 planar used in the 20 MHz -061
model.
486/33PD3-P70LP (DX)
and 486/33PS3-P70LP (SX) for the 38F6973/56F9085 planar used in the 16
MHz -031 and 20 MHz -121 models.
(Photos are Copyright © 1993, Kingston
Technology Corp.)
Note that I have also seen the 20 MHz -061 planar used in the -121 model. It
is important that you get the right model for your planar, as the orientation
of the CPU socket is different and the upgrade will not physically fit if it is
not the correct one.
Fellow PS/2'er Karsten Harder was kind enough to send me a 486/33PD3-P70LP
fitted with an AMD 486DX-40 CPU from the factory (thanks, Karsten!).
Installation was simple and straightforward, and nicely documented in the
Kingston manual. If the planar is fitted with a 387DX math coprocessor, it must
be removed (even if you only have the SX upgrade). After properly setting the
four DIP switches, the machine booted and seemed to run fine (although it
seemed to take much longer to initialize the POST routines on power-up). I see
no reason why clock doubled or tripled CPU's could not be used with this
upgrade, space inside the P70 permitting. I did test the upgrade with an Intel
486DX4ODPR-100; it came up fine, and benchmarks reported a
CPU speed of 120 MHz. Be careful when removing the CPU from the circuit board;
the Kingston board is quite thin, and is very susceptible to damage. The
DX4ODPR is tall enough that the heatsink will prohibit the use of a long card
adapter in the 32-bit MCA slot, however. The SX version should accept a DX CPU
without trouble. The downside: you are still using the slow (by comparison)
planar memory. The lack of L2 cache also hinders performance. Still, it is a
worthwhile upgrade if you can't find a MCMaster card.
The best performing CPU upgrade for the P70, by far, is the Kingston/AOX
MCMaster 486 cards. My machine is currently running with a 25 MHz MCMaster that
I managed to overclock to 32 MHz (yes, 32 MHz, not 33). See
Fred Spencer's page for the info on how I
accomplished this. Interestingly, the only CPU that would run reliably with a
32 MHz base clock on this board is an IBM (Cyrix) Blue Lightning DX4-100. An
Intel DX2-66ODPR and an AMD 5x86-P75ADZ (with interposer) would both lock up
after a random period of time running Windows. The problem did not appear
related to cooling, so my conclusion is that some of the components on the card
are slightly speed sensitive. I would be interested in hearing from anyone who
has successfully used clock-multiplier CPU's on a true 33 MHz MCMaster. As
mentioned above, I had to disable the planar memory in
the MCMaster setup, as the machine would generally refuse to boot once the
MCMaster took over. Disadvantages of the MCMaster upgrade: actually finding
one, although they do seem to show up on eBay occasionally (surplus auctions
are also a good source, it's a good bet that any university or government
agency that bought a lot of PS/2's will have a few floating around); it takes
the only 32-bit full-length MCA slot, which limits your options for adding
other cards; and you need a CPU heatsink without a fan, because there simply
isn't enough room for a fan. This shouldn't be a problem, as cooling seems to
be adequate for a CPU with heatsink only.
My little P70 (a.k.a. "Punkzilla, fastest P70 in the west") is
currently running the MCMaster with the IBM DX4-100 CPU and 24 MB of RAM, and
runs PC-DOS 2000 and Windows for Workgroups 3.11 very well. I have a 3Com
Etherlink III network card (with the blue handle removed) in the 16-bit slot,
and it barely fits. I have the computer set up to track Ham Radio satellites
with Logsat Professional 5.1, and it has
come in handy as a portable satellite tracking computer. I've got an AUI
transciever for the network card so I can connect to either coax or
twisted-pair networks, and have used the machine with both NETBUI (Windows) and
Novell networks. The transciever and the reference disk fit neatly inside the
I/O cover, and all I need is to run the reference disk to tell the network card
which port I want to use. These upgrade attempts have successfully turned what
some would consider a slow, old dinosaur into a very usable machine for service
work, portable word-processing or database functions, or just about any other
use you can come up with. Add a decent-sized SCSI hard disk with a Future
Domain MCS-700 controller (at the expense of losing the network card), and it
would probably even run Windows 95 comfortably (not that I would actually WANT
to...).
|
386DX-20
20 MHz -121
w/387DX-20 |
Kingston 486 Now!
@40 MHz
AM486DX-40 |
Kingston 486 Now!
@40/120 MHz
i486DX4ODPR- 100 |
Kingston MCMaster
@32/96 MHz
IBM 5x86-3V3- 100HB |
Kingston
MCMaster
@32/128 MHz
AMD 5x86-133 |
Kingston MCMaster
@32/96 MHz
i486DX4ODPR- 100 |
CPU
Clock |
20.028 |
40.027 |
120.126 |
93.99 |
128.149 |
96.124 |
CPU
Bench. |
23.98 |
129.23 |
129.25 |
440.57 |
432.54 |
352.49 |
FPU
Bench. |
48.55 |
309.24 |
406.99 |
1032.04 |
1013.00 |
775.63 |
Video
Bench. |
610.00 |
614.00 |
614.00 |
508.00 |
511.00 |
509.00 |
The Benchmark Scores (Landmark Speed V2.0, PC-DOS 7.0R1)
Hard Disk
The P70 uses a DBA (direct bus attachment) ESDI hard disk, that is not
compatible with anything else except the PS/2 Models 55sx and 70 desktop
computers. Thus, a P70 with a 30 or 60 MB hard disk may be upgraded with a 120
MB disk from a Model 70. Brad Parker and Thomas J. Watercott have sent me info
about an 8570-161 that has a 160 MB ESDI drive in it. I have verified this
through the EPRM, and Thomas relates that he has successfully used this drive
in a P70. This is probably the best source of replacement/upgrade hard disks
for the P70. As an aside, these drives are referred to by some (and reported by
a lot of diagnostic software) as "IDE", but don't bear much resemblance to IDE
as we know it today. Peter Wendt has this to say on the subject:
"Don't forget that IDE was not very common in the late 80s ... and mostly
ignored by IBM as "silly stuff" (what it is). They developed a lot ESDI-based
stuff and treated HDs as ESDIs - not only because it is easier to use 64 heads
/ 64 sectors as basis and re-calculate the (lower) number of cylinders rather
than dealing with odd sector / cylinder and head numbers. This is mostly done
with the adapters hardware already - and the BIOS is "ESDI focused" - the
drives true geometry however totally differs in fact.
"But what. The generic term "IDE Intelligent Drive Electronic" is used for
most drives that have controller and harddisk mechanism in one physical unit -
in contrast to the "classical design" with separate (unintelligent) harddisk
and separate controller - disregarded, which encoding / translation or writing
method they *technically* use. Therefore Carlyle is right in a way.
One *could* nonetheless define it more accurate and set the borders a bit
tighter - and limiting the term "IDE" to the Conner / Seagate / WD creation
invented for "small inexpensive desktop harddrives", which actually use an
enhanced / expanded / watered ST-506 specification and RLL 2.7 or such stuff.
"Who cares anyway ? I would not hit anyones head for using the term "IDE"
for the IBM PS/2 DBA2 MCA ESDI so-many-acronyms-in-a-row") drives. The real
name for harddisks should be "SCSI" at all - or nothing."
If you need more than 160 MB, you will have to go SCSI with an add-in
card. I will not go into detail on this, since it is described nicely
by Bob Eager HERE,
using an IBM SCSI adapter. This is a 32-bit SCSI card,
so if you use one of these, forget about putting in a RAM card or an MCMaster
processor card. If you need your 32-bit MCA slot for other goodies,
another SCSI adapter ideally suited to the P70 is the Future
Domain MCS-700 (short-card version). The MCS-700 is a 16-bit
SCSI-2 card capable of 10 MB/s transfers, has a standard SCSI-2 external
connector, and also has a power connector on board to supply power to the
hard drive. It is not, however, a busmaster; it has no onboard processor
and uses PIO mode for data transfers. It is still a very nice controller;
I used one in my Model 95 as a secondary controller, and it ran a CD recorder
and two hard disks without a hiccup. Louis Ohland has a nice page
on the IBM OEM version of the MCS-700.
The IBM version (found mainly in the Model 76s/77s "Lacuna" machines) should
be equally usable in the P70; however, it lacks the onboard power connector.
The solder points for the connector are still there, so it is easy to add
in if you are comfortable with a soldering iron. A ROM BIOS upgrade
(version 3.61) was available from Adaptec
at no charge or from HERE.
P75 Information
The P75 can be described as a P70 on steroids. It boasts a redesigned
planar with a i486DX-33 MHz CPU on a plug-in processor complex, as
well as an embedded SCSI subsystem to replace the P70's direct ESDI attachment
bus. Internal SCSI hard disk options were 160 MB and 400 MB.
The SCSI subsystem may leave something to be desired, however; one user
that I know of has installed a Future
Domain MCS-700 SCSI-2 controller in his P75 and reports better performance.
Casolai sent along this P75 SCSI info (21 Jan 2001):
I read the note on your site about the MCS-700 being faster than the built-in
SCSI. So I searched for one on Ebay. It is a LOT faster than the integrated
SCSI!
With a program called SYSCHECK, it shows the following:
Original SCSI with Conner 540meg SCSI-2-Fast drive
Seek = Immediate
Transfer Rate = about 160k to 170k per second
MCS-700 SCSI-2 card with Conner 540meg SCSI-2-Fast drive
Seek = Immediate
Transfer Rate = 270 to 280k per second
I also got a 16 bit Micro Channel IDE card on Ebay, and it benchmarked
really well:
"Procom Technology MC PIRA" with "Quantum 270meg Maveric Prodrive IDE"
Seek = 16 ms
Transfer Rate = 950 to 980k per second
The IDE card is completely automatic, and I can't adjust the BIOS settings
manually as far as I can tell. It won't take any decent sized drives, even a
normal IDE 540meg shows up as "Drive not supported" on the boot screen. I tried
to install EZ-BIOS, but since the IDE BIOS isn't even recognizing the drive at
all, the BIOS overlay can't work.
I'm still using the 540meg SCSI drive in the P75, and I installed Windows
95a to see how well it worked. It ran great with good speed and I didn't have
any trouble getting online with it either.
Cas contributes further to the state of the art (18 Mar 2001):
With Windows 95 installed, when you tell it to restart in MS-DOS mode, the
plasma screen goes black and you can't see anything. The MS-DOS mode is
working, but nothing is shown.
The Ardent Tool page has a note
about the XGA-2 card doing the same thing on a 9590 system. Peter said to add
this line to the C:\WINDOWS\DOSSTART.BAT file:
mode co80
If the file is not there, create it and add the line.
On my P75 it fixed the black screen problem!
To fix the IRQ problem when adding an IBM brand SCSI card to a P75
thats running Windows 95:
Only ONE of them can be used with windows 32bit drivers.
Check the memory IO address of both of them using the Reference disk,
and
write it down.
Start Windows 95 in safe mode, go to the Device Manager, and REMOVE the
hard disk, and the built-in IBM SCSI controller.
Restart windows normally, with the hard disk connected to the SCSI card
you want to use instead of the planar SCSI controller.
Run the Add New Hardware wizard, and when it finds two IBM SCSI Controllers,
click Finish.
Windows will ask if you want to restart to activate the new hardware, click
NO.
Go to the Device Manager, and look at the IO address of the 2 new SCSI
controllers that are listed. REMOVE the one that matches the IO address of the
planar controller, leaving only the card type controller.
Restart windows normally
The card should now be working, and your hard disk should now be listed in
the Device Manager also.
Remember, if you ever run the Add New Hardware wizard again in the future,
you MUST remove the planar SCSI controller each time. Or windows will lock
up during startup since it cannot handle two Micro Channel SCSI controllers
on the same IRQ (14). Also, you CANNOT use the planar SCSI at all when
windows is running, this includes the external plug.
This was done when I installed an IBM "SCSI with Cache" controller.
This procedure assumes you already have Windows 95 installed. If you don't,
use the planar SCSI and install windows, then add the SCSI card per these
instructions after windows is already completely setup.
Here is a new benchmark to add to the ones I sent you before:
IBM SCSI with 512k Cache Controller with Conner 540meg SCSI-2-Fast drive
Seek = 12.63 ms average
Transfer Rate = 916k per second
Talk about a massive improvement over the Future Domain card!
You can see Casolai's web site HERE (archived).
Beware of multimedia content! :-)
Peter
Wendt provides the following info on the video subsystem:
The P75 has XGA-1 with 1MB VRAM.
The internal display however supports only the 640 x 480 mode and turns off
if any of the higher modes is used. This will explain why you can get a
(hi-res) picture on the external screen but not on the plasma.
You will have to stay at the low-res mode here, since the display is from
the principle only a "generic VGA screen" (same as on the P70 BTW).
Here you are. You can use the XGA full features only with an external
monitor.
The P75 video subsystem differs into 2 segments. The VGA for the plasma
display and the XGA for the external port. Both are linked when running in VGA
mode - but separated once the XGA functionality is used.
The IBM redbook GG24-3616-00 (dealing with the P75 subsystems) defines it as
follows:
"Plasma display adapter with XGA graphics capabilities to external displays"
and "640 x 480 / 16 grey scales plasma display".
System memory was 8 MB standard, upgradable to 16 MB on the planar. In
addition to the I/O connections found on the P70, the P75 I/O panel has an
RS/6000 style external SCSI connector. The machine also has one more of each
(16- and 32-bit) MCA expansion slots, for a total of four MCA slots. One 32-bit
slot is an AVE slot. The extra slots
make the case slightly deeper than the P70. I've been told that the P75 was
marketed as a "portable server"; based on my experiences, it could certainly
fulfill that function quite well.
Mark's P75 still had the original price tag attached!
| 8573-161 |
160 MB SCSI hard disk |
| 8573-401 |
400 MB SCSI hard disk |
P75 Model Number Breakdown
P75 CPU Upgrade
Unfortunately, there isn't a lot the average person can do to upgrade the
CPU in the P75. The fact that the processor complex is on a plugin card
suggests that IBM may have intended it to be upgradable, but no upgrade is even
rumored to exist. The CPU itself is soldered to the circuit board, so popping
in an Overdrive isn't an option. However, there are two possibilities for those
willing to go to the time and trouble.
The first, and most viable option for most people, would be to find one of
the Kingston MCMaster 33 MHz cards. There were versions of this card with
clock-multiplied CPU's, but they seem to be extremely rare. More common are the
486DX-33 and 486DX/SX-25 versions of the card, which should be able to support
faster CPU's. A 33 MHz base card with a DX2-66 or faster CPU fitted should
perform nicely. The advantage of this approach is that you can also easily
upgrade memory beyond the 16 MB limit of the planar, with better performance
than adding a memory card to the MCA bus. The disadvantages are the loss of one
32-bit expansion slot to the upgrade card, and the height limitation on the
CPU/heatsink combination imposed by the limited space inside the P75. The
hardest part would be locating one of these cards, but one place I have seen
them for sale fairly often is eBay.
The second approach is the more difficult, and should only be attempted by
experienced hardware hackers. I have personally upgraded four P75's by
desoldering the CPU from the processor board and installing a 168-pin PGA
socket. This SHOULD NOT be attempted unless you have a
lot of soldering experience AND access to professional
desoldering equipment; it is very easy to damage the copper traces on the
board. That being said, the results were well worth it. The two 'local'
machines ran very well with an AMD 5x86-133 CPU chip (with 3.45-volt
interposer). Various other "turbochip" upgrades should work equally well; one
of the two machines currently has a i486DX4-100 Overdrive CPU installed,
running Windows NT 4.0 very nicely. I don't think the P75 BIOS supports
write-back cache, so any "turbochip" should have the capability of running in
write-through mode for best results. The disadvantage to this method, other
than the risk of destroying your CPU board, is the height limitation imposed by
the cramped quarters inside the P75. Some of the CPU/interposer/heatsink
combinations are quite tall, and will limit the use of the two adjacent MCA
slots to short cards only; even at that, some 32-bit "short" cards may still be
too long.
Photos of one completed CPU upgrade can be found on Tam Pham's page
here.
On the subject of write-back cache, Brad Root has this to say:
Don't know about the Kingston Turbochip but the
Evergreen is no go in WT or WB. The good news - the Trinity Works PowerStacker
works in both modes very well on the P75.
P75 CMOS Battery Replacement
It's about that time, folks. It is the second week of June, 2001, and the
battery in my P75 (manufactured May, 1991) has failed. Unfortunately, this is
not an off-the-shelf replacement. The P75 uses a custom battery pack consisting
of two Panasonic CR2477 1000 mAh cells in series, soldered to a small circuit
board with a plastic cover. Bob Eager has a nice pic of the pack on
this page. Look
here for Louis Ohland's pic of the
circuit board with the cover snapped off.
The problem is, the CR2477 (with solder tabs) is not something you can just
run down to your local battery shop and grab off the shelf. They are somewhat
more expensive than a 'standard' CMOS battery, and must be ordered from a parts
distributor. Assuming that there is nothing unusual about the CMOS memory/clock
in the P75 (as compared to the Model 95, etc., that use the more standard and
common CR2032 220 mAh cell for CMOS retention), there is no reason that I can
see for using the CR2477 other than greatly extended CMOS battery life. Two
CR2032 coin cell holders liberated from 'retired' clone boards will fit nicely
inside the battery pack shell. They can be fixed in place with hot melt glue or
epoxy and soldered with short jumper wires to the pads that the CR2477s
connected to. Two CR2032s cost me USD$1.36 each at the grocery store today.
Much better than the $4-$9 each (plus shipping) that Bob found for the CR2477!
Top it off with a small chunk of non-conductive foam or bubble
wrap to keep things secure inside the battery case, and the result is an
inexpensive replacement solution that looks stock from the outside. The CR2032
only has about 22% of the capacity of the CR2477, so expect to replace them
about every 2.5 years instead of every 10 years.
Y2K
The P70 8573-121/MCMaster 486 and P75 8573-401 that I have tested both pass
as being Y2K compliant under IBM PC-DOS 2000. PC-DOS 2000 (or PC-DOS 7.0 with
Y2K patch) handles the rollover to 2000 and properly updates the century byte
in CMOS. Both machines fail the year 2000 progression test when booted under
MS-DOS 6.22, requiring manual intervention to update the century byte. The
reboot test after manually setting the date to 1-1-2000 passes. With the proper
operating system or software patches to ensure CMOS rollover, both machines are
100% Y2K compliant. Testing was done using YMARK2000, from
NSTL. A very good technical discussion of
Y2K compliance from a hardware standpoint, courtesy of Peter Wendt, can be
found HERE. IBM has a very nice white paper
on Y2K, available
HERE.
Acknowledgements
I would like to thank the following people, without whom this page
would not have been possible: Mark Stewart (Mr. Grench), for the
loan of his beloved P75; Martin Adams, for the info on the Microram 386
RAM card; the "MCA Mafia" and the denizens
of comp.sys.ibm.ps2.hardware,
especially Peter Wendt for his boundless knowledge of everything PS/2 and
Louis Ohland for kicking me in the rear and getting me working on this
page; IBM Corporation for giving me the tools
to understand these machines, years before I ever actually owned
one; and finally, the surplus property divisions of the State of Nebraska
and the University of Nebraska-Lincoln, for selling all this neat stuff
for really cheap at auctions.
P70/75 Links
IBM P70/75 Hardware Maintenance Manual (dead)
IBM 8573 Support Page (Reference disks are here) (dead)
IBM Service Parts (dead)
Bob Eager's P70 Page
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