TechNotes		August 11, 1995  Vol 1 No 10
Copyright (c) 1995 Dynamic Learning Systems.  All rights reserved worldwide.

Table of Contents
-------------------------
A. Disclaimer and Cautions
B. About TechNotes
C. About Dynamic Learning Systems

1. Communications
		Interlink Cabling

2. DOS and Windows
		Searching for 256 Colors

3. Drives and Displays
		Overriding the Write-Protect
		Dueling Monitors
		Ghosts in the Machine

4. Manufacturers and Parts
		Ringing Packard Bell
		
5. Memory
		The Nearly-Dead Battery
		72 to 30 Adapters
		The Question of Parity

6. Motherboards, Ports, and Busses
		A New Laptop CPU
		A Noisy CPU Fan

7. Printers
		Speeding the Slow Printer


Disclaimer and Cautions
------------------------------------
	This document is COPYRIGHTED under international law.  This document is provided as an educational service by Dynamic Learning Systems, and is intended to benefit all readers.  Although this document is copyrighted, you may print and re-transmit this document freely, so long as the document is used in its entirety, and credit is given to Dynamic Learning Systems.

	THIS DOCUMENT IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND/OR FITNESS FOR A PARTICULAR PURPOSE.  The reader assumes the entire risk as to the accuracy and the use of this document.  All PC service and maintenance involves some element of personal risk, as well as risk to the equipment involved.  If you are not comfortable following the information contained herein, refer the work to more qualified personnel.  ALWAYS BACKUP VITAL INFORMATION IF POSSIBLE BEFORE ATTEMPTING ANY TYPE OF SERVICE.


About TechNotes
------------------------
	TechNotes is a compilation of symptoms and solutions for various PC problems.  A new release of TechNotes is released every two weeks.  We welcome your contributions of symptoms, as well as solutions that you have found to your own PC problems.  We also encourage you to contribute enhanced or alternative solutions.  It is our hope to make TechNotes a first-rate tipsheet for PC and peripheral service.  The file name of each TechNote includes its release date.  For example, a file name TN040795 indicates a TechNote (TN) date of April (04) 7th (07), 1995 (95).

About Dynamic Learning Systems
----------------------------------------------
	Dynamic Learning Systems specializes in PC upgrade, maintenance, and troubleshooting topics for electronics/computer enthusiasts and technicians.  We publish The PC Toolbox newsletter.  If you have any questions or contributions for TechNotes, or wish to obtain subscription information for The PC Toolbox, feel free to contact us:

	Dynamic Learning Systems
	P.O. Box 805
	Marlboro, MA  01752  USA
	Fax: 508-898-9995
	CompuServe: 73652,3205
	Internet: sbigelow@cerfnet.com


SECTION 1. Communications
=======================

INTERLINK CABLING

Q. Can you give me the wiring details for a cable to connect two computers together using their parallel ports?  I need to use the MS-DOS Interlink (as well as other transfer programs) to transfer files between various computers.  

A. This turns out to be a rather popular request, so we'll provide several different pinouts here.  We also suggest that you check your DOS help file "help interlink" for more details.  The FastLynx file transfer utility (or its older version FastWire), and its companion EtherBox mini-network utility, can operate either in serial or parallel mode.  Here are the cabling requirements.  Good-quality shielded cable is strongly recommended for maximum speed and minimum susceptibility to interference.  The shield braid can also form one of the required connections, and this is noted for each case in its connection table below.

Serial Cable

A 7-wire Null-modem scheme is used between Serial (COM) Ports:

One end:                       Other end:
DB25  DB9      function        DB9  DB25

2     3        TXD - RXD       2    3
3     2        RXD - TXD       3    2
4     7        RTS - CTS       8    5
5     8        CTS - RTS       7    4
6     6        DSR - DTR       4    20
7     5        GND - GND       5    7     (Shield)
20    4        DTR - DSR       6    6

An alternative for the serial cable's grounding (for the DB25 version ONLY) is to connect pins 7 (GND - GND) by an individual wire, and connect the shield to pin 1 (Frame Ground) at each end.  This option is NOT available for DB9 connectors, although the shield COULD be connected to the DB9 connector frames at each end.  

Parallel Cable

5 wires (4 data bits and a strobe) are connected from data outputs to status inputs on the LPT (parallel) ports.  Inputs of one are connected to outputs of the other, and vice versa.

One end:     Other end:
2      ->    15
3      ->    13
4      ->    12
5      ->    10
6      ->    11
10     <-    5
11     <-    6
12     <-    4
13     <-    3
15     <-    2

Ground wires are common to both ends.
18 to 25 <-> 18 to 25     (Shield)


SECTION 2. DOS and Windows
============================

SEARCHING FOR 256 COLORS

Q. From time to time, I get messages from various Windows applications that colors will not be displayed properly without a 256 color display.  Is it possible to enable this?  This unit is an i386DX, 8MB RAM, 425MB HDD, using Windows 3.11 with 32-bit access on, a permanent swap file of 24MB, and DOS 6.22.

A. You need a Windows video driver for your card (one that supports 256 colors).  If one didn't come on a disk with your video card or computer, you'll have to download it from ftp.microsoft.com.  Try searching for "Cirrus video drivers".  Any Cirrus 52xx drivers should work with your card.  Copy (or unzip) all the files into a temporary directory, then go to Windows Setup.  Select a new video mode, and choose the "Unlisted or updated" option.  Type the name of your temporary directory when it prompts you to insert a disk - it should now give you a list of available new video modes on that driver set.  Choose one with 256 colors.  You will then have to leave Windows and reboot.  That should take care of it.


SECTION 3. Drives and Displays
==========================

OVERRIDING THE WRITE-PROTECT

Q. Do you know if write-protecting a diskette physically prevents a drive from writing to it?  Could controller calls (in theory) still write to a write-protected diskette?  Do you know of any drive controllers that allow writing to a write-protected drive?

A. Now that's an unusual question.  You see, write-protecting a floppy diskette does not "physically" prevent writing.  The IBM-compatible floppy disk drive checks the condition of the diskette's write-protect notch.  When a disk is write-protected, a sensor in the drive sets a control line on the floppy cable which tells the controller that the diskette id write-protected, so when a write command is sent, the controller returns an error code (which usually translates back to a "write protect error" message).  As a consequence, it is impossible to "force" the controller to override the write-protect signal.  Now, some (non-IBM) floppy disk systems handle write protection in software, so it could be possible to force writing, but no IBM FDDs or controllers allow writing when the write-protect is engaged.

DUELING MONITORS

Q. I have a Diamond Stealth Pro SVGA video board and an older ISA VGA board.  I would like to use both video cards and configure a two-monitor system.  Is there a way to do this?

A. Well, no.  It is possible to have a monochrome (MDA) video board and a VGA or SVGA video board in the PC together since the MDA and VGA/SVGA memory ranges do not conflict.  However, it is not possible to separate a VGA and SVGA video board which use the same memory ranges - the conflict would disable both cards (no video), and probably crash the PC.  On the Mac, it is possible to have up to 6 video boards and monitors running simultaneously.

GHOSTS IN THE MACHINE

Q. I'm a user of an NEC SyncMaster 17Glsi, but there are some minor problems.  My 17Glsi monitor is very unstable in 1208x1024 mode - a blurred shadow of image is imposed slightly right of the original image.  I recently bought an NEC GLsi and it shows exactly the same symptom.  After some fiddling, I found out it gets worse with higher resolutions and frame rates.  At ~80Hz in 1152x864 mode, it is quite bearable.   How do such shadow images arise?  Is there anything I can do about it?  I wonder if the output from the graphics card has an influence here.

A. The symptoms you describe are known as "ghosting", and are typically the result of noise in the video signal cable between the video adapter and the monitor.  Ghosting is most often encountered when a monitor is being run close to its rated bandwidth, or if there is a fault in the video signal cable.  The more data that is being pumped through the video cable, the more susceptible the video cable is to noise and impedance effects (or mis-matches).  Unfortunately, there is really little that can be done about this - it is a limit of the monitor's design.  You can switch over to a video adapter and monitor using high-quality shielded video cables or BNC cable assemblies.


SECTION 4. Manufacturers & Parts
=============================

RINGING PACKARD BELL

Q. I am desperately searching for contact information for Packard Bell.  Do you have any contacts that you could share?

A. We sure do!  You can contact Packard Bell Tech Support at 800-733-4411 (this is a very busy line).  You can also try the Packard Bell BBS at 801-250-1600, or send a Fax to 801-579-0092.  If you have a connection to CompuServe or Prodigy, you can explore forums and send messages at GO PACKARD BELL (CompuServe) or JUMP PACKARD BELL (Prodigy).


SECTION 5. Memory
================

THE NEARLY-DEAD BATTERY

Q. I have a bizarre problem with my system - it does not keep track of the date and time while it is turned off.  For example, if I turn off the system and start it a day later, it will have the date and time when I last turned it off.  Yet, it keeps good time while it is on, and I do not loose any of the system configuration information.

A. This is one of the most mis-understood CMOS problems in the industry - you're battery is almost dead, OR it is not making proper contact with the motherboard.  You see, the CMOS backup battery is not needed while the PC is running, but when you turn the system off, the nearly-dead battery does not provide enough energy to run the real-time clock (RTC), but it does have enough energy to hold the values in CMOS memory.  If the battery is new (or replacing the battery has no effect), then there is a problem in the motherboard battery connection.  For example, the electrode that holds down a coin cell may be oxidized or not making good contact.  Effectively, there would be no battery in the system.  In that case, there is obviously enough capacitance in the battery circuit to hold up CMOS memory (at least for a few days).

72 TO 30 ADAPTERS

Q. Is it possible to use 72-pin SIMMs in a motherboard that only supports 30-pin SIMMs?  Is there any type of adapter for this purpose?

A. Unfortunately, there is not.  While there are adapters that will allow you to gang 30-pin SIMMs together for a 72-pin SIMM slot, there is no way to "break down" a 72-pin SIMM for use in a 30-pin slot.  The reason is that the 72-pin SIMMs are 32-bits wide, and the 30-pin SIMMs are only 8 bits wide.

THE QUESTION OF PARITY

Q. I have a relatively new motherboard that has slots for my old 30-pin SIMM (1x9).  This new board also has a couple of 72-pin SIMM sockets, that I can use without removing the old memory.  My question is, must I use 1x36 (parity) SIMMs, or can I get away with 1x32 (non-parity) SIMMs?

A. This is an easy question to answer, but there are some caveats.  Older motherboards demanded the use of 1X9 and 1X36 (parity) memory.  In the effort to save money, however, some PC manufacturers are abandoning the use of parity, so many newer motherboards can accept "parity" OR "non-parity" memory so long as ALL the memory in the PC is the same type.  So if you choose to buy cheaper non-parity memory, you will have to replace ALL the SIMMs in your PC.  Often, you must also set a motherboard jumper (or disable a CMOS setup parameter) to shut off parity checking.
	We recommend the use of parity.  While parity failures are rare, at least the fault will halt the system without allowing erroneous commands or data to wreck havoc on your PC.  The price for non-parity RAM is only about $3-$5 (US) cheaper per MB than parity RAM, so you really don't save much money, and there is no performance advantage for the PC itself.


SECTION 6. Motherboards and Busses
===================================

A NEW LAPTOP CPU

Q. I have been thinking of upgrading the hardware in my Toshiba T4600 laptop - namely the i486DX/33 CPU.  I would like to install an i486DX2/66.  Is this possible?  How would I go about it?

A. First, you can't just yank out one CPU and drop in another.  To be upgradeable, a CPU must be socket-mounted (as opposed to being soldered into place), and the CPU socket must be Overdrive-ready - that is, designed to accept a clock-multiplied CPU.  I suggest that you check the user manual that came with your laptop.  It will likely outline the available upgrades - if an Overdrive CPU is mentioned, then you're all set - just select a compatible Overdrive CPU.  However, I doubt that such an option is available due to the extra heat that would be generated by the i486DX2/66.  There is simply not enough room for a heat sink.

A NOISY CPU FAN

Q. I am curious about a motherboard that I just bought.  It is a National Advantage (IBM owned company) i486DX2/66 board.  I have been very satisfied with the power of the motherboard, but the problem is the CPU fan - it is very noisy.  Do all CPU fans have the same high-pitched buzz that this one does?  Any comments?

A. It may just be a cheap CPU fan.  Try changing the pressure on the CPU fan by adjusting the clips that hold it to the CPU.  I have seen several that have become noisy, but they can often be quieted by re-seating the fan.  If this fails to correct the noise, go ahead and replace the CPU fan - they're not too expensive.


Section 7. Printers
==============================

SPEEDING THE SLOW PRINTER

Q. I have recently inherited a used Epson ActionPrinter 3250.  It prints well enough, but it prints very slowly.  Is there anything I can do to accelerate its speed?

A. Well, there are several things you can try, but dot-matrix printers such as the ActionPrinter are simply slow by nature.  First, it doesn't matter whether you are using a serial or parallel interface - both should be more than fast enough to keep the printer's buffer filled.  Now, if you are printing in high-quality (or "letter-quality") mode, you can speed printing by reducing the print quality - this will reduce the number of passes the print head makes for each line of print.  If you are printing under Windows, try increasing the priority of the Print Manager, and make sure that you are using the very latest printer driver for optimum performance.  Still, printing under Windows is always graphic-oriented, so it will tend to be slower than ASCII printing under DOS.

