Open the Case
How to fix a "Broken" Door
Plasma Display Information
VGA, CGA and EGA resolutions
Color graphics contrast
Text mode contrast
External PS/2 displays
Color to Gray Mapping
Plasma Display Brightness
Close Plasma Display
What is the Plasma Display?
Why does Plasma Display Get So Hot?
"Cool" Windows Color Schemes
Remove Hard Drive
Miniture Right Angle KB Plug Identity
Minature KB Connector Pinout
External Storage Device Port
External Storage Device Cable
ESD Cable Pinout
ESD Cable Hosiden Connector Pinout
Remove power On Password
Jim Shorney's "The P70 Project" (P70 and P75 Stuff)
Locate the Type-Model
Opening the Case
NOTE: There are two
additional catches, one to each side of the carrying
handle.When you lift up the rear cover, it pivots on
How to Fix a "Broken" Door
From Us, the god-Emperor of Microchannel
How many times have you seen the ports cover hanging loose off of a P70 or P75? Chances are, it ain't broke, just discomboobulated.
Open the case. (unscrew the three captive screws, pry out and up on the bottom edge). Pull up on the bottom edge and rotate it up on the pivots at the top rear of the case.
Look at the slots where the ports door hinges enter the case body. See the wide end? If you look on the interior of the case on the opposite of the wide ends, you will notice a pivot point for the metal hinge to fit into.
Remove the ports cover by pressing the hinge inwards (relative to the port cover).
Look at the "U" shaped arms of the hinge. Are they straight out from the metal strip? They should be at right angles to the metal strip. If they aren't, _carefully_ bend them so they are.
Now reinsert the hinges through their slots and pop the hinge points back into the matching pivots. You may have to carefully press the hinges inwards, since the pivots have a lip around them. Shut door.
If the hinges want to pop free, carefully bend them
outwards just a little more, so more force is exerted
against the pivots,
Plasma Display Information
The computer has a gas plasma display that shows program colors in up to 16-level monochrome shades with a VGA of 640 X 480 resolution. Some programs may not be designed to take full advantage of the plasma display, or could benefit from minor changes. Here are some tips for best results.
CGA and EGA resolutions-Programs
using CGA and EGA resolutions are supported by this
display; however, program screens will not use the
entire plasma display area, and graphics shapes could be
slightly distorted. How much area of the plasma display
is used by VGA, CGA, and EGA is illustrated in the
figure below. For best results, use the version of a
program that supports VGA resolution.
Color graphics contrast-The
plasma display automatically converts program colors
into different monochrome shades. Some programs start
with colors that lose contrast when converted. You can
usually change colors from within the program to help
increase the contrast.
A program will not start; parts of a program screen are missing-Some graphics programs, for example, Microsoft Windows i386 versions 2.1 and below, may not recognize the graphics capabilities of the plasma display and other PS/2 monochrome displays. This could appear as start-up difficulty, or faded/missing information. To correct this situation, put the plasma display (or the attached PS/2 monochrome display) in graphics mode before starting the program. To do this, type MODE CO80 at the DOS prompt, then press Enter.
Text mode contrast-The contrast in text (non-graphics) programs is best when the plasma display is in two-shade text mode. The display is in this mode when the computer is turned on, but could be put into graphics mode by a program. To return the display to text mode, type MODE MONO at the DOS prompt, then press Enter.
Auto-dim feature-The plasma display is automatically turned off to extend its life if no data is received from the system or entered from the keyboard or an auxiliary device for 10 minutes (default value). The default value can be changed by using the backup copy of the Reference Diskette. To change the default value, go to the Auto-Dim Time. The following shows the path to the Auto-Dim Time.
Main Menu>Set Configuration>Change Configuration>Auto-Dim Time
There are two ways to turn on the display again:
If the mouse picks up vibration from a desk which turns on the display again, change the Auto-Dim Reset from Keyboard and Aux. Device to Keyboard Only. The following shows the path to the Auto-Dim Reset.
Main Menu>Set Configuration>Change Configuration>Auto-Dim Reset
External PS/2 displays-The computer supports all PS/2 displays with VGA resolution. If you use the same program with the plasma display or an external PS/2 display, the best choice for program colors could change depending on the display you are using.
Color to Gray Mapping-There are some applications that are developed for color displays but can be used on monochrome displays. When using such applications, reset the Color to Gray Mapping to Green Signal Only. Setting RGB Mixed Signals (default value) may result in an unpredictable display image. The following shows the path to the Color to Gray Mapping.
Main Menu>Set Configuration>Change Config>Color to Grey Remapping
default value, Primary, turns on only one display that
is considered by the system to be the primary display.
When no external PS/2 display is connected to the system
unit, the plasma display is considered the primary
display and only VGA mode is supported. But when an
Configuration>Change Config>Turned-on Display
Plasma Display Brightness
You can reverse the brightness of standard text and emphasized text in DOS through a simple command, BRT. This command lets you set standard text brighter than emphasized text, or vice versa. The Reference Diskette contains this command program and a program to install it. When you attach an external PS/2 display or use certain programs, the brightness is not selectable. That is, emphasized text is always displayed with brighter characters.
How to Install the Brightness
After Installing the brightness program, use the following instructions on how to change the brightness level.
To Change the Brightness Level
Close Plasma Display
First push back the lower edges into the case. Now push
the upper edges back into the case. Seems odd, but it
Another cousin within that technology is the "Nixie" display tube, where the multiple cathodes are formed like numbers, letters and signs. Or the Beckman / Sperry "flat panel displays" (early multi-segment displays) of the 70's. Modern plasma screens (as used in flatscreen TVs) are basically the same technology, but there is an additional layer with RGB triplets that light up when the underlying neon cell is activated. Brightness control is very tricky and mostly achieved by pulse-width modulating the corresponding cell. A cell can only be on or off, altering the applied voltage results in only marginal brightness change (below 10%). Therefore "new" plasma screens are an interesting mix of very old and very new technology. The basic technique goes back to the Geissler tubes of the 19th century, over the neon lamps of the late 19th and early 20th century and needs todays complex and fast computer / microcontroller support to work at all - generating the appropriate column / row / intensity control signals.
Their advantage over TFT LCD is the far lower count of active elements - resulting in an immanently higher reliability and lower production losses as well as the absence of a "backlight". They are self-illuminating screens.
Why does the screen on the P7x get
The controller circuits are soldered
directly to the back of the screen. Both - the
gas-discharge element and the controller circuits give
up some heat which is neither dangerous nor unnormal.
That's all. These screens are a high-voltage technology
unlike to LCD-screens (these black on whites as used in
most modern laptops) - these LCDs are low-voltage /
indirect lighting technologies - however the lamp to
backlight them is a high-voltage again. The
plasma-display is a high voltage / direct lighting
screen, which needs no backlight.
The main disadvantage: some higher power-consumption, normally not possible to feed it from batteries, somewhat complicated shading / contrast control. Main advantage: rigid, temperature independent (while self-heating :-) ), not very much pressure sensitive. Makes a good hand-warmer in cold times .... !
"COOL" Windows Desktops
Plasma Control PCB M480L640HB53 (single row connector plasma screen)
Hard Drive Removal
KB Plug Identity
The P7x right angle connector is HRS # CL231-3004-2, part # 3130A-6PA Go to the Hirose Electric web page and look at their catalog HERE
T. Sunagawa sez:
27 Nov 01- Trying to convert between the four pin header and the common PS/2 port. My urge is to allow installing a short female PS/2 plug to stick an external PS/2 keyboard on. You might even want to create your own extension cable, because finding the special extension cable is about as likely as finding Elvis in your kitchen.
David Beem wrote:
Pin 2 = +5VDC (Red on mainboard connector)
Still trying to get an "M" apart for
External Storage Device Port
The external storage device port is the equivalent of the B drive internal diskette port, as found in the PS/2 Model 70. This permits attachment of externally powered devices like the IBM 4869 External Diskette Drive Model 001 and some other equipment manufacturers' backup devices.
PIN I/O Signal PIN I/O Signal
1 N/A Ground 2 I - Second Drive Installed
3 N/A Ground 4 O - Reduced Write Current
5 N/A Ground 6 N/A Reserved
7 N/A Ground 8 I - Index
9 O - Motor On 1 10 O - Drive Select 1
11 N/A Reserved 12 N/A Reserved
13 N/A Ground 14 O - Direction
15 N/A Ground 16 O - Step
17 N/A Ground 18 O - Write Data
19 N/A Ground 20 O - Write Gate
21 N/A Ground 22 I - Track 00
23 N/A Ground 24 I - Write Protect
25 N/A Ground 26 I - Read Data
27 N/A Ground 28 O - Side 1 Select
29 N/A Ground 30 I - Diskette Change
NOTE: NC means No Connector, there is nothing in the socket.
External Storage Device Cable
P/N 23F2716 / FRU 23F3230
On the left is the DB37 connector that mates with the 4869 signal cable. On the right is the Hosiden HDI-30 connector that plugs directly into the P70/P75 external storage device port.
This side shot of the HDI-30 plug hints at the spring loaded collar. To release the tension on that spring tip at the upper left, pull the collar (using the ribs) down toward the P70/P75 planar while pulling the cable back from the planar.
Storage Device Cable Pinout
P70 Trivia (applies to P75 some)
The system I am using sometimes refuses to start after power-on without any display or beep symptom. After several power on-off eventually it starts. Any idea???
On various occasions I saw failing mainboards. They refused to come on - and I don't know why. They simply died from one day to the next and could only be replaced. Back in the "good old days" with full IBM support and machines under warranty that was no big problem. Today things look different. If cleaning the power supply doesn't help - and if removing all adapters and testing with the bare sysboard doesn't change the misbehavior: suspect the mainboard to be damaged and look for a replacement.
Under rare circumstances a poorly seated card-riserboard caused trouble. Have the small two-slot riserboard removed, clean the contacts and spray a good amount of TV-tuner cleaner in the board connector. Let it dry for 10 minutes and use a piece of stiff card pushed into the connector with one edge and move it up / down the connector. Then spray the connector once again and let it dry for an hour. You might also repeat these steps on the two MCA slots on the riserboard. Especially on the slot pointing towards the top of the unit, which collects dust when left with no card installed for a longer time.
Some older units also developed a sort of "creeping short" along the FDD cable where the FDD cable enters the "flip out" FDD bay. There was an ECA for the FDD cable from IBM for the earlier models, where FDD cables broke, shortened DC-voltages to GND or FDD signals and caused a dead systemboard. (Few only - IBM fixed it in an early stage).
Another potential problem has been reported with the memory modules. The system takes only 1 and 2MB modules anyway, but certain 2MB modules installed on the sysboard connectors with double sided 10 chips layout (20 chips total - 2 x 8 data + 2 x 2 parity - 16 bigger and 4 smaller chips) caused overload of the memory driver lines. This usually resulted in either a 200-something memory error -or- a machine failing to come up at all.
I take from the 16MB you'd mentioned that the upper slot contains a memory card (the lower is too short anyway). So you should probably check the card connector as described further above and check if you cannot use memory modules with lower amount of chips. Usually the memory installed on cards causes a 200-series memory error in first place before dumping the machine to total darkness - but you never know.
I have several P70 in my collection and all of these
run with double-sided 2MB chips ... but I had a customer
machine in '93 or so, which didn't. We used later
2MB/70ns 9-chip modules "hardware-recoded" (with
soldering) to 2MB / 85ns and the system worked like a
Remove Power-on Password (P75 shown, P70 similar)
To remove an active, unknown, power-on password do the following.
1. Power-off the computer and unplug the power cord.
2. Remove the system-unit cover.
3. Short the two pins of JP1 together.
With the pins shorted, power-on the computer. This
erases the power-on password. Remove the short after
POST is finished.