-Paul G. Crumley -Information Technology Center -Carnegie-Mellon University -Pittsburgh, PA 15213 -GContents -G Introduction ........................................... 1 -G Requirements ........................................... 2 -G Description of Modification ............................ 3 -G Parts List ............................................. 4 -G Modification Instructions .............................. 7 -G Debugging Tips ........................................ 22 -G Special Thanks ........................................ 24 -G Card Map .............................................. 25 -G Feedback .............................................. 26 -Contents ii -GE-INTRODUCTIONHF- -This document provides a set of instructions for modifying -the IBM PC-Jr Internal Diskette Drive Adapter to allow the -connection of a second diskette drive to the PC-Jr. -This modification requires alterations to the diskette -adapter which will certainly void your warranty. Though I -have tested this modification extensively and have not had -any reported failures to date (yes, some people have had -problems but so far all the diskette drives have ultimately -worked) there are no guarantees. Also, this modification -should be treated as IBM Internal Use Only. I believe that -it would be inappropriate to pass this on to the outside -world. This modification is NOT supported in any formal -manner and is NOT endorsed or approved by anyone or -anything. If you have any questions about the use of this -modification please direct your questions to me, Paul -Crumley, CMUPGC at PGHVM1. -Enough of this, you get the idea. The adventure begins! -Introduction 1 - IBM PC-Jr Internal Diskette Drive -GE-REQUIREMENTSHF- -HFþ Hardware - HF- PC-Jr - HF- 1 internal diskette drive and adapter -HFþ Software - HF- DOS 2.1 or higher - HF- A diskette with a copy of the file 2NDDISK.DBG - This is not required. This is only needed if you - want the patches to DOS to be done automatically - for you. This must be downloaded in BINARY - format. I uploaded it using E78COPY with the /B - option. -Requirements 2 -GE-DESCRIPTION OF MODIFICATIONHF- -By following this set of instructions you will make the -following modifications to the IBM PC-Jr Diskette Drive -Adapter: -HFþ Make a new cable to connect the second diskette drive - to the PC-Jr diskette adapter. -HFþ Make the following modifications to the diskette - adapter: - HF- Add a latch that will provide the drive select - logic for the second diskette drive. - HF- Add a buffering chip that will drive the needed - signals on the cable that will attach to the second - diskette drive. -HFþ Assemble the second diskette drive in its case and - attach it to the PC-Jr diskette adapter. -HFþ Patch the boot record of your DOS diskette so the - second diskette drive is recognized and used. -This modification should be compatible with almost all -software. The PC-Jr BIOS is designed to access up to 3 -diskette drives. This hardware modification allows I/O -ports that are already defined for BIOS to be used to -enable the second diskette drive. Unfortunately, in order -for the BIOS to know about the existence of the second -diskette drive, more hardware is needed than this simple -modification. It would be very difficult to modify the -present diskette adapter to supply this hardware solution. -For that reason I have chosen to have you patch your DOS -boot record so that BIOS will be told to use the second -diskette drive. Since the support for the second diskette -is contained in the BIOS and not in DOS there should be -very few problems with compatibility. -If you desire, you can also patch the FORMAT command that -comes with DOS 2.1 so that all diskettes that you format -will have this patch applied automatically. -Description of Modification 3 -GE-PARTS LISTHF- -The modification requires the following parts: -HFþ 1 74LS175. -HFþ 1 7438. -HFþ 1 .1 uF disk capacitor rated at 15 volts or greater. -HFþ 1 16 pin socket for the 74LS175. Use solder tail - rather than Wire-Wrap sockets. Get the best sockets - you can find. Gold plated if they are available. -HFþ 1 14 pin socket for the 7438. As above. -HFþ 6 ft Wire-Wrap wire. 30 or 32 gauge Wire-Wrap wire - works well for these connections. -HFþ 3 ft 34 conductor ribbon cable. The grey kind if - fine. No need for the expensive multicolored stuff. -HFþ 2 ft 34 conductor edge connectors. If you look at - the original cable that connects the PC-Jr diskette - adapter to the diskette drive the edge connector is at - the end that attaches to the diskette drive. -HFþ 1 ft 34 conductor Berg connector. If you look at the - original cable that connects the PC-Jr diskette adapter - to the diskette drive the Berg connector is at the end - that attaches to the diskette adapter. -HFþ solder. Use the thinnest solder you can find. -HFþ masking tape. Just a couple of inches is all you - need. -HFþ glue or silicone bathtub sealer. These may be needed - to hold some of the wires down on the card so they are - not touching the case or other parts. The silicone - bathtub sealer usually works best. -HFþ 1 double sided diskette drive. See below. -HFþ 1 enclosure and power supply for the diskette drive. - See below. -HFþ 1 double sided diskette. This is used to make a new, - patched version of the DOS boot diskette. -The tools required include: -HFþ soldering iron. (25 Watts if you have only one. see - below) -Parts List 4 -HFþ unsoldering bulb. -HFþ diagonal snippers. -HFþ needle-nose pliers. -HFþ wire strippers that work with the small gauge wire. -HFþ flat blade screwdrivers -- a small and a medium sized - one. -HFþ vice or clamps to hold the card while you work. -HFþ magnifying glass. -HFþ old toothbrush. -HFþ a ruler. -HFþ scissors that can cut the ribbon cable to the correct - length. -HFþ a knife such as an X-acto modelling knife should be - fine. -HFþ a pen that will write on the masking tape. -HFþ vise or other pressing device to use to squeeze the - connectors onto the ribbon cable. -HFþ any tools that will be needed to assemble the case and - power supply you are going to use. Things like nut - drivers and pliers might be useful. -Prose descriptions of some of the above: -The choice of soldering iron is a very personal matter. I -have three different ones, 12, 25 & 50 Watts, so I can -match the iron to the job at hand. If you plan on having -only one, a 25 Watt iron is probably the best choice if it -has a sharp, clean tip. A 12 Watt iron with a sharp tip is -probably the best to use for the soldering process while -the 50 Watt monsters should be avoided for soldering but -can come in handy for unsoldering parts. -One of the inexpensive unsoldering bulbs available at -places like Radio Shack will come in quite useful when you -must remove the solder from some holes along one side of -the card to install the sockets. More expensive and exotic -unsoldering tools should not be needed for this task. -When selecting the sockets I recommend using the best you -can find. Mechanical connections are the first place to -look when there is trouble. Use good parts and save -yourself some grief later on. -Parts List 5 -You should purchase an extra 74LS175 and 7438 just in case -one of these parts is damaged in shipping or when it is -being installed. Extra sockets might also be a good idea. -These parts should be available from a number of -companies. A good place to look is in the back of -magazines such as Byte or Radio Electronics. Many of these -companies have a minimum order so it might be worth looking -around for a place where you can get all of the parts you -need so you will be above the minimum order. -There are a number of companies that make IBM PC compatible -drives. TEAC, Tandon, Qume, and CDC come to mind quickly. -Basically, if the diskette drive works in a PC or PC/XT you -should have no problem using it with the PC-Jr. Watch out -for Apple and Atari compatible models. -When selecting an enclosure and power supply for the -diskette drive make sure the power supply has both 5 and 12 -volts available. You might be able to find the diskette -drive and the enclosure/power supply as a "package deal" if -you shop around a little bit. I would recommend looking -for a enclosure and power supply that is sold as a unit -rather than buying them separately. If they are bought as -a unit you can be sure everything will fit together well -and there should be fewer "surprises." -Make sure that the enclosure and power supply come with the -proper power cable needed to attach to the diskette drive -and also make sure that a 120 volt wall plug cable is -included. You should ask to make sure that the enclosure -and power supply are fused and if they are U. L. and CSA -approved. Anything that has 120 volts going into it can be -dangerous so buy a quality enclosure and power supply and -save yourself future problems. -Once all of this is collected you are ready to proceed. -Parts List 6 -GE-MODIFICATION INSTRUCTIONSHF- -This modification is carried out in a series of steps. -There are checkpoints along the way to help isolate errors -to a small number of connections thus providing a more -manageable debugging process if something goes wrong. -This modification is geared to someone that has experience -soldering and working with electronic parts. If you don't -feel comfortable with a soldering iron you may like to ask -a friend to help you with the soldering steps of this -modification. If you work slowly and carefully you should -set aside two to three hours to complete this -modification. -You also must know how to identify pin 1 of IC chips. If -you look at the top of chip you will see a notch or dot at -one end. If you point that end of the chip towards you, -the closest pin on the right is pin 1. The pin numbers go -down the right side then back the left. The numbering for -16 and 20 pin chips is similar. The following diagram -should help: - --------------- - / / ! - / / ! - / # / /! - / / ! ! - / t / /! ! - / r / ! ! ! <---- pin 7 - / a / /! ! ! - / P / ! ! ! - / / /! ! ! - / __ / ! ! ! - / / / / /! ! ! - / / / o / ! ! ! - ------------ / /! ! ! - ! ! ! ! ! - ------------ /! ! ! - ! ! ! - ! ! ! - ! ! - pin 14 ----> ! ! <---- pin 1 -The method I present has the nice property of being easily -removed. Nothing is cut. Parts are only added to the -diskette adapter card. If you must remove this -modification you can restore the card to its original -state. -Modification Instructions 7 -Get out your soldering iron, here we go! -HF1. Read ALL the instructions before starting!!!!! -HF2. The second time through this list check off each step - as it is completed so that you are certain that all the - the steps are done properly. -HF3. Make and test a new cable. - HFa. Make sure the diskette drive and adapter work. - This shouldn't be a problem with old PC-Jrs. You - know they work if you use them all the time. If - you just bought a new PC-Jr I would recommend using - it for a couple of days to make sure everything - works correctly. This modification will void your - warranty on the diskette adapter and maybe on the - whole PC-Jr. By running the PC-Jr for a few days - you should flush out most of the possible - manufacturing defects. Do try to use the machine - for at least 10 to 15 hours as 10 minutes of - service won't bring out the problems too well. - After testing, turn off the PC-Jr and remove the - power cord from the wall. - HFb. Open the case of the PC-Jr by gently prying up at - the rear of the seam around the top of the case. - The back of the cover will will lift up while the - front of the cover is held in place by a lip - attached to the front of the PC-Jr case. After the - back of the cover has started to lift up pull the - cover towards the rear of the PC-Jr. This will - free the front of the cover and the cover can be - removed. - HFc. Locate the Diskette adapter by finding the wide - grey cable that is attached to the diskette drive. - Follow that cable to towards the left of the case. - The diskette adapter is at the left end of this - cable. - HFd. Remove the diskette adapter by grasping both the - front and rear of the card at the same time and - gently pulling the card up. Pull gently as the - card is still attached to the cable. - HFe. Remove the cable from the diskette adapter by - firmly gripping the connect (not the cable) and - pulling the connector straight away from the card. - Be careful to not bend the small pins on the card - when you remove the cable. - HFf. Set the diskette adapter aside in a safe place for - now. - HFg. Remove the other end of the cable from the diskette -Modification Instructions 8 - drive using the same technique as was used to - remove it from the diskette adapter. You don't - have to be quite as gentle as with the card since - there are no little pins to bend but be gentle - anyway. - HFh. The new cable will look something like this: - __ __ - ! ! ! ! - _ ! ! ! ! - ! !----------!__!--------------------------------------<===>--!__! - ! ! - !_!<-- 8" -->! !<------------------- 2'-2" ----------------->! - HFi. Using the old diskette cable as a model make the - left part of the new cable to the same dimensions - as the old cable while leaving the excess cable - hanging off toward the right. The connector for - the second diskette drive will be placed at the - right end of this cable. The left most connector - will be installed first. This is the Berg - connector not one of the edge connectors that - attaches to the diskette drives. - HFj. If you look at the connector carefully you should - be able to find one end of the connector marked - with pin 1 or a small arrow will be etched into the - connector shell. Line this end of the connector up - with the striped side of the cable. This will help - you keep the connectors oriented correctly. The - connectors are attached to the cable by first - lining up the bulges in the insulation of the cable - with the teeth of the connector. The connector - should have a channel the correct width for the - cable to fit in making the bulges line up - correctly. - HFk. After the cable is positioned correctly place the - back part of the connector over the cable. This is - a bit hard to describe but I think it should be - pretty easy to figure out how all this fits - together. Place this assembly in a vise or other - type of clamp and slowly press the back of the - connector into place. The teeth will be cutting - into the cable's insulation. Go slowly and be - careful that everything is going together - properly. - HFl. Repeat this operation for the second connector - making sure you have the pin 1 ends of both - connectors pointing in the same direction. This - will be the edge connector that is attached to the - middle section of the cable. -Modification Instructions 9 - HFm. Now, using the old cable as a model, make a crease - in the new cable so it will fit in the PC-Jr - correctly. - HFn. Test this new cable by plugging it into the - diskette drive and the diskette adapter, replacing - the diskette adapter in the PC-Jr, plugging the - PC-Jr into the wall, and turning on the PC-Jr. - There is no need to put on the top completely. - Just set it on the PC-Jr so you will not - accidentally touch the power supply or drop - anything inside the PC-Jr while the power is turned - on. After you have verified the cable works turn - off the power and unplug the PC-Jr. Remove the - diskette adapter and this new cable and prepare to - attach the connector for the second diskette - drive. - HFo. If the PC-Jr's diskette didn't work correctly with - the new cable try the old one to make sure - everything is hooked up correctly. If the old - cable works, carefully inspect the new cable to - make sure that the connectors are attached - correctly. look for twisted or misaligned parts of - the ribbon cable in the area where the teeth cut - through the insulation. You should be able to pry - the backs off the connectors if you exercise some - care. With three feet of ribbon cable you can cut - the used section off and try again if you have to. - HFp. This is perhaps the hardest part of the - modification task so take your time and work - carefully. To make the drive select signals - connect to the correct pins you have to make two - slits in the cable forming three sections of - conductors. The center section is twisted one half - turn and then this resulting group of 34 conductors - is attached to the rightmost edge connector. The - completed connection should look something like - this: - -- - ===========================================! ! - 1 ! 1! - ! ! - ! ! - ! ! - 9 ! 9! - ===-------========! ! - 10\ / 16 !10! - cable 11 \ / 15 !11! connector - \ / ! ! - ! ! ! - ! ! ! -Modification Instructions 10 - / ! ! - 15 / \ 11 !15! - 16/ \ 10 !16! - ===-------========! ! - 17 !17! - ! ! - ! ! - ! ! - 34 !34! - -------------------------------------------! ! - -- - HFq. If you are familiar with the PC's diskette cable - you have a better picture of what you are making - than I can represent here. If available, use the - PC cable as a guide. Starting with the conductor - for pin 1 count over 9 conductors and slit the - ribbon cable between the ninth and tenth - conductors. Make the slit about 6 inches long - being careful to not damage the insulation. Count - over 7 more conductors and slit the ribbon cable - between conductors 16 and 17. COUNT CAREFULLY. - HFr. The cable will now be in three sections. Twist the - center section and press the last edge connector - into place leaving the outer sections of ribbon - cable flat. It can take a bit of work to get - everything into alignment before the connector is - pressed together so take your time and get it - right. - HFs. Test the cable again in the same manner as you - tested it above. -HF4. Modify diskette adapter card. - HFa. Clean away some workspace, put down some old - newspaper if it is needed to protect your work - surface, and plug in your soldering iron. Get a - drink (alcohol and hot soldering irons don't mix!) - and relax while you are waiting for the iron to - heat up. - HFb. Set the adapter in front of you oriented as is - shown in the card map located near the back of this - document. Along the right side of the adapter you - should see two vertical rows of solder dots. These - dots are holes that are filled with solder. The - new parts that are needed for the second diskette - drive will be placed in these holes. - HFc. Before the sockets for the new parts can be - installed, the holes that the pins for these socket - will use must be cleaned out. This is done with - the unsoldering bulb. Mount the adapter in your - vise or other type of clamp so that it is fairly -Modification Instructions 11 - vertical rather than flat. If the two rows of - solder-filled holes are at the top it might be - easier for you to do the next few steps. The - procedure for removing the solder from the holes - is: - HF1) Grab the unsoldering bulb with one hand. - (usually the left of right-handed persons, the - right for left-handed ones.) - HF2) Hold the hot soldering iron with the other - hand. (yes, you have to put down that drink - now!) - HF3) Squeeze the bulb and place its tip near one of - the solder-filled holes. - HF4) Place the tip of the soldering iron on the same - hole, but on the opposite side of the card. - HF5) Wait for the solder to melt and then quickly - release the bulb thus sucking the solder out of - the hole. - HF6) You may have to repeat the above two steps for - some holes to get them cleaned out. - HF7) Move on to the next hole and repeat the above - three steps. - HF8) Continue this operation until all the holes - along that side of the adapter are clean. - HFd. Use the magnifying glass and CAREFULLY check to - make sure that no small globs of solder are left on - the card or have slid under any of the other - chips. Use the old toothbrush to scour away any - solder deposits that are stuck on the adapter. - When all the deposits are gone you may continue. - HFe. It is now time to mount the sockets for the new - chips. Look at the card map again. It shows that - the 7438, a 14 pin chip, should be located near the - top of the card and the 74LS175, a 16 pin chip, - should be located at the bottom of the card. Get - the 14 and 16 pin socket. If you look at the - sockets closely you should see some type of marker - that is used to indicate which pin is pin 1. - Usually the pin 1 corner is bevelled. Using the - card map as a guide place the make sure pin 1 is in - the proper corner. When you place the sockets, - position them at the extreme ends of the rows of - holes. - HFf. Position the .1uF disk capacitor between the two - chips so that one of the leads in in one row of -Modification Instructions 12 - holes and one lead is in the other. You may have - to bend the leads around a bit to make them fit. - Be gentle since they can break off if they are - handled too roughly. You should have everything - placed something like this: - ---------------------------------------------------------------- - ! ! - ! O . . . . . . . . . . . . . . . . . . ! - ! --------------------- --- ------------------------ ! - ! ! ! ! ! ! ! ! - ! !> ! ! ! !> ! ! - ! !o ! ! ! !o ! ! - ! -------------------- --- ----------------------- ! - ! . . . . . . . . . . . . . . . . . . ! - ! ! - ! ! - ! 14 pin 16 pin ! - ! Socket for .1 uF Socket for ! - ! 7438 Capacitor 74LS175 ! - ! ! - HFg. Use a piece of masking tape to hold these parts in - place when the card is turned over to be soldered. - HFh. Turn the card over. If something shifts because - the masking tape was not tight enough go back and - make sure all the parts are pressed firmly against - the card. - HFi. Solder each of the sockets and the capacitor to the - card. For now, leave about 1/4 inch of the .1 uF - Capacitor sticking out the back of the adapter and - cut off the rest. - HFj. Go back with the magnifying glass and check for any - solder globs that could be causing shorts between - the pins of the chip. - HFk. If your pen will write on the adapter make a mark - at the pin 1 position of the two sockets. This - will help you find the correct pin position when - you are connecting wires to the sockets. If your - pen won't write on the adapter use a piece of - masking tape. - HFl. Now you finally get to start connecting the new - chips to the circuit. These connections should be - made on the back of the adapter. You should be - VERY careful when locating the pins since the pins - are all in different places when view from the back - than they are when viewed from the front. Recheck - each connection as it is made to make sure you have -Modification Instructions 13 - the right pins connected. - HFm. Connect pin 8 of the 74LS175 chip, IC5 on the chip - map, to one lead of the .1 uF disk capacitor. - Connect this same lead to pin 7 of the 7438 socket, - IC1 on the card map, and pin 8 of the 74LS175 - socket, IC2. Make these connections to the - capacitor as close to the card as possible. - HFn. Connect pin 16 of IC5 to the other lead of the .1 - uF disk capacitor. Connect this same lead to pin - 14 of IC1 and pin 16 of IC2. Now cut off any extra - length of the leads on the .1 uF capacitor. - HFo. Connect pin 1 of IC5 to pin 1 of IC2. Connect pin - 9 of IC5 to pin 9 of IC2. You are now done with - IC5. - HFp. Locate the 74LS245 at position IC3. Connect pin 17 - of IC3 to pin 4 of IC2. You are now done with - IC3. - HFq. Connect pin 2 of IC2 to pins 1, 2, 4 & 5 of IC1. - You are now done with IC2. - HFr. Cut two pieces of wire about 12 inches long. - Solder one end of one of these wires to pin 3 of - IC1 and solder one end of the other wire to pin 6 - of IC1. You are now done with IC1. - HFs. At this point all connections to the chips should - be completed. IC4 was not touched, it was only - labeled to help you find IC3 and IC4. You should - have made 4 connections to IC5 while IC3 had only - one connection. IC1 and IC2 have many unused pins. - Check to make sure that the following pins are have - no connections: - HFþ IC1 -- pins 8, 9, 10, 11, 12 & 13 - HFþ IC2 -- pins 3, 5, 6, 7, 10, 11, 12, 13, 14, & - 15 - HFt. Now we will make the connection to the ribbon cable - connector. Orient the adapter so that the chips - are facing the table and the diskette cable - connector is in the far right corner. You should - see something like this: - ------------------------------------------------------------- - ! - o-o---o-o-o-o-o-o-o-o-o-o-o-o-o-o ! - ! - o o o o 5 o 7 o o o o o o o o o o ! - ! -Modification Instructions 14 - o o o o o o ! - ! - o o o o o o o o o o o o o o o ! - ! - HFu. Notice that the far row of pins are all connected - together and the third pin from the left in that - row is missing. The pins marked 5 and 7 are were - we are going to attach the signals we need to - control the second diskette drive. Connect one of - the 12 inch wires to pin 5 and connect the other to - pin 7. It doesn't matter which wire goes to 5 and - which goes to 7. What does matter is that you make - the connections to pins 5 and 7. You should cut - off most of the excess wire before making these - connections so that you don't have these wires - dangling about when you are done with this - modification. - HFv. Go back and check all of these connections again to - make sure they are correct. Incorrect connections - can lead to ruined chips so be thorough. Check - that the proper pins are connected and also check - the solder connections to be certain that none of - the adjacent pins are shorted to one another. Look - for wires where much of the insulation has been - melted away from the pin connection. If there is a - danger of the bare wire touch some nearby pin or - one of the traces on the board redo the - connection. - HFw. Test the adapter again as you have done in the past - to make sure it is still operating correctly as a - single diskette adapter. If the PC-Jr works fine - continue. If things don't go as planned look for - incorrect connections and soldering mistakes. The - section with debugging tips may be helpful. - HFx. Now get the 7438 and 74LS175. Make sure you have - identified pin 1 for both chips and insert them in - their respective sockets. the 7438 goes in socket - IC1 and the 74LS175 goes in socket IC2. Be gentle - while inserting the pins in the socket. The pins - are rather fragile and bend quite easily. If - disaster should strike and one of the pins does get - bent don't panic. Simply use a small screwdriver - to pry the chip out of the socket, use the - needle-nose pliers to straighten the injured - appendage, and try again. - HFy. With IC1 and IC2 installed test the adapter once - again. If everything works correctly continue. If - there are problems check the connections and solder - joints for problems. -Modification Instructions 15 - HFz. When you are convinced the adapter is working - correctly you can unplug the soldering iron and set - it aside. Hopefully it won't have to be plugged in - again for this project. - HFaa. Use some of glue or silicone bathtub sealer to - fasten the loose wires securely to the adapter. - This will help prevent accidental damage to the - connections by catching the wires on something and - pulling one of the wires loose. -HF5. Install the diskette in its enclosure and connect the - cables. - HFa. It is difficult for me to give specific details on - installing the diskette drive in the enclosure and - connecting the power supply since I don't know what - kind of diskette drive or enclosure you will have. - Some general things that must be done include: - HFþ Make sure the diskette drive is securely - mounted so that the connections will be less - likely to vibrate loose with use. - HFþ Make sure that pin 1 on the ribbon cable is - connected to the pin 1 end of the edge - connector on the diskette drive. Check this - twice just to be sure. - HFþ Make sure the power cable is connected - properly. If the 4 conductor plug came - preattached to the power supply this shouldn't - be a problem. If you are using a "homebrew" - design be careful, mixing up the connections - will have disastrous results. - HFþ Leave room for the ribbon cable to get out of - the cabinet. Try not to bend the cable or - pinch it too much at this could lead to - reliability problems later. - HFþ If possible, get an enclosure and power supply - as a unit so you know everything will fit - together well. - HFþ For safety reasons don't have the power supply - plugged into a wall power outlet when you are - working in the cabinet with the cover removed. - HFb. After the new diskette drive is mounted and the - power cable and ribbon cable are connected you can - proceed to the next step. Keep the cable routing - in mind as you install the diskette so you don't - have to change things around too much when the - covers are installed. -Modification Instructions 16 - HFc. Place the new ribbon cable on the modified diskette - adapter card and insert the adapter card in the - PC-Jr. - HFd. Attach the new cable to the internal diskette - drive. - HFe. Recheck these connections. - HFf. As you have done so many times before test the - PC-Jr to make sure it still works as a single - diskette system. Test the PC-Jr first with the - second diskette drive's power supply disconnected - from the wall power outlet. If that works - correctly turn off the PC-Jr, plug the second - diskette drive's power supply into the wall power - outlet, turn on the second diskette, and turn on - the PC-Jr. If everything still works correctly - continue on with the final part of the - modification, modifying the software to use the - second diskette drive. If there are problems go to - the section on debugging tips. -HF6. Patch the DOS 2.1 diskette. - HFa. The DOS boot record must be altered so that BIOS - will be told that two diskette drives are available - rather than just one. By patching the boot record - DOS does know that the BIOS data area has been - altered insuring a great amount of software - compatibility. - HFb. If these next instructions sound too simple minded - and you are offended please accept my apologies. - We hardware types like to leave nothing to chance. - "Better precisely wrong than vaguely right." - HFc. Using the DISKCOPY command make a new DOS 2.1 - diskette. This is done by placing the original DOS - diskette in the internal diskette drive and - rebooting the system. After DOS has booted and you - get past the time and date questions type "DISKCOPY - A: A:" and press the ENTER key. The DISKCOPY - should prompt you from there. Just remember that - the SOURCE diskette is the original DOS diskette - and the TARGET diskette is the new diskette you are - making. - HFd. Next copy the DEBUG command to the new diskette. - Insert the new diskette in the internal diskette - drive and type "COPY B:DEBUG.COM A: /V" then press - enter. When the system asks to have diskette B: - inserted USE THE INTERNAL DISKETTE DRIVE and press - ENTER. The DEBUG program is on the Supplemental - Programs diskette that comes with DOS 2.1. You - will be asked to place the target diskette in drive -Modification Instructions 17 - A:. Put the new DOS diskette back in the internal - drive and press ENTER. After the COPY command has - completed check that DEBUG has been copied by using - the "DIR A:" command. - HFe. Now you have a choice to make. If you can download - the file of DEBUG commands that I have sent you as - 2NDDISK.DBG you can use the Standard Input - facilities of DOS 2.1 to have the new diskette - patched for you. If you can not download the file - 2NDDISK.DBG you will have to enter the DEBUG - commands yourself. I will first describe how to - use the file 2NDDISK.DBG. - HF1) First, you must get the file 2NDDISK.DBG on a - diskette. This file must be downloaded in - BINARY format. I used E78COPY to upload this - command to VM. Make sure you have a good copy - of the file before you do anything. If you are - not sure if your copy is OK check it against - the instructions listed for those that can not - download files. They should be a perfect - match. (except the square brackets in - 2NDDISK.DBG will be shown as ('s and )'s - below.) - HF2) You must copy the file 2NDDISK.DBG to the new - DOS diskette in the same manner you copied - DEBUG.COM. Use the command "COPY B:2NDDISK.DBG - A: /V". - HF3) Next, use the command "DEBUG < 2NDDISK.DBG" to - run the DEBUG program. DEBUG will take all of - its commands from the file 2NDDISK.DBG and - display what it is doing on the screen. You - should see the following scroll by on the - screen as DEBUG executes: - -L 0100 0 0 1 - -U 0100 L 5 - 0906:0100 EB2C JMP 012E - 0906:0102 90 NOP - 0906:0103 49 DEC CX - 0906:0104 42 INC DX - -A 0100 - 0906:0100 OR BYTE PTR (0410),40 - 0906:0105 JMP 012E - 0906:0107 - -W 100 0 0 1 - - - -N FORMAT.COM - -L - -U 19F8 L 5 - 091A:19F8 EB2C JMP 1A26 - 091A:19FA 90 NOP -Modification Instructions 18 - 091A:19FB 49 DEC CX - 091A:19FC 42 INC DX - -A 19F8 - 091A:19F8 OR BYTE PTR (0410),40 - 091A:19FD JMP 1A26 - 091A:19FF - -N FORMAT2.COM - -W - Writing 1B00 bytes - -Q - HF4) If this goes as expected you are done making a - new DOS diskette. A new version of the FORMAT - command called FORMAT2 has also been created on - your DOS diskette. If you use this "patched" - version of the FORMAT command to make new - diskettes the alterations for the second - diskette drive will be applied to the boot - record automatically. - HFf. Even if you must type in the DEBUG commands - yourself you should not have too hard a time - altering your DOS diskette so that you can have - access to the second diskette drive. - HF1) Place the new diskette in the internal drive - and type "DEBUG" then press ENTER. - HF2) When DEBUG is ready to accept commands it will - display a dash ("-") character. Simply type in - the following list of commands. Remember that - the ('s and )'s are square brackets. After - each line is typed press ENTER. For the blank - lines just press ENTER. The screen should look - just like the script shown above for the - automatical DEBUG session. This should allow - you to check your work. - L 0100 0 0 1 - U 0100 L 5 - A 0100 - OR BYTE PTR (0410),40 - JMP 012E - W 100 0 0 1 - N FORMAT.COM - L - U 19F8 L 5 - A 19F8 - OR BYTE PTR (0410),40 - JMP 1A26 - N FORMAT2.COM - W - Q -Modification Instructions 19 - HF3) If this works correctly you have just made a - new DOS diskette. A new version of the FORMAT - command called FORMAT2 has also been created on - your DOS diskette. If you use this "patched" - version of the FORMAT command to make new - diskettes the alterations for the second - diskette drive will be applied to the boot - record automatically. - HFg. You should mark this diskette as a special PC-Jr - diskette that will only work with a modified - PC-Jr. If you try to use this modified diskette on - any PC that doesn't have two diskette drives DOS - will become rather confused. There should be no - problem moving data with these diskettes, just - don't use them to boot the system. -HF7. Test your work. - HFa. This is the time to pause for a moment and reflect - on your life, say prayers, perform superstitious - acts, etc. This is a very personal step. You know - what you have to do at this time so do it. - HFb. Turn off the PC-Jr and place the modified DOS - diskette in the internal diskette drive. Turn on - the power to the new diskette in its cabinet then - turn on the PC-Jr. After DOS boots you should have - the use of both drives. If there are any problems - continue on the the next section of debugging - tips. -HF8. Replace the covers. - HFa. Turn off the power to the PC-Jr and the second - diskette drive and remove their power plugs from - the wall outlet. - HFb. If you look at the top edge of the right side of - the PC-Jr case you will see that IBM thoughtfully - left a slot for this cable near the rear of the - PC-Jr case. Fold the cable neatly, lay it in the - slot, and replace the PC-Jr's cover. - HFc. Again, it is hard for me to know just how to tell - you about installing the cover(s) on your second - diskette drive cabinet. Some general things to - keep in mind are: - HFþ Make sure the ribbon cable is not being pinched - by any of the covers. - HFþ Make sure the ribbon cable is does not have any - kinks or strange twists in it. If you must, -Modification Instructions 20 - make a neat crease in the cable to allow it to - make its way out of the cabinet. - HFþ Check the other wiring inside the cabinet to - make sure none of the wires or cables will come - in contact with any of the moving parts of the - diskette drive. - HFþ Try not to block any ventilation slots when - routing the cables. - HFd. Well, this is the final test. Plug the second - diskette and the PC-Jr back into the wall power - outlet, make sure the modified DOS diskette is in - the internal diskette drive, turn them on, and.... - HFe. If everything goes well I recommend taking another - break, getting another drink and relaxing for a - moment before you start to clean up the mess you - made. If there are problems I insist you take - another break and get a drink (remember about hot - soldering irons!) before continuing. Many problems - look better after a little time away from the - project. -Modification Instructions 21 -GE-DEBUGGING TIPSHF- -If something doesn't work, experience with the modification -shows that almost all of the problems are with soldering. -Make sure there are no shorts created by any of your solder -joints. Check the 74LS175 very carefully as it is easy to -accidentally solder two pins together by accident. Also -check the wires that attach to the connector to make sure -there are no shorts there. -After that, recheck all the connections for accuracy. -Check the connections made on the back side of the card -carefully since it is easy to get the pin numbers mixed up -when you are working on the back of the card. -If you still have problems send a note. I will help with -problems on a "when time permits" basis. -Here are some simple tests you can do to help isolate the -problem. -HF1. If nothing happens when you turn on the switch - something big is wrong. The first thing to check is - that the PC-Jr is plugged into the wall outlet and that - the transformer is still plugged into the back of the - PC-Jr. These connections can get bumped loose with all - the movement that goes on. If these are OK, remove the - adapter and try the PC-Jr again. If everything works, - (and it should) try the adapter again. If the adapter - fails like this the most common problems are: - HFa. A solder bridge has formed shorting the power - supply. - HFb. One or more chips are installed backward. These - chips destroy themselves when power is applied and - short the power supply. -HF2. If the original drive doesn't work try using the - original cable to check that the new cable is wired - correctly. If the original cable works OK try the new - cable without the second drive connected. -HF3. If the second drive doesn't work try installing the new - drive as the internal drive. You don't have to - physically install the drive, just make the cable - connections. This should test the second diskette - drive. -HF4. Sometimes either drive will work alone but the two - drives will not work when both are connected to the - cable. This usually means that the cable is not - properly constructed or there is a problem with the - 7438 and its wiring. -Debugging Tips 22 -These tips should give you some idea of where to start -looking if you have a problem. -Debugging Tips 23 - IBM PC-Jr Internal Diskette Drive -GE-SPECIAL THANKSHF- -Bill Brown provided valuable information regarding the -proper buffering of the diskette control signals. The -diskette drives require special signal conditioning and I -had neglected this need in my first set of instructions. -Special Thanks 24 - IBM PC-Jr Internal Diskette Drive -GE-CARD MAPHF- -This diagram points out the important areas of the card to -help aid in the locating of the connection points used in -this set of instructions. - ------------------------------------------------------------------- - ! ..............x.. ------------------- ! - ! ..........b.a.... ! 765 ! o I: ! - ! o------------------ : C: ! - ! : 1: ! - ! --------- ------ ------- : : ! - ! ! IC3 ! ! IC4! ! IC5 ! : : ! - ! o-------- o----- o------ o I: ! - ! : C: ! - ! : 2: ! - ! : : ! - ! !! :::::::::: !! ! - ---------------------------- ------------ ----------------------- - Chips towards you -In the above diagram: -HFþ The 765 is the biggest chip on the card. -HFþ a and b are the pins to which you connect the signals - from the 7438. -HFþ o indicates pin 1. -HFþ The 74LS175 and 7438 are mounted in sockets you solder - into place. -HFþ x is a pin that is missing. It is used as a key on the - original cable. -HFþ IC1 shows the placement for the new 7438. The o - indicates pin 1. -HFþ IC2 shows the placement for the new 74LS175. The o - indicates pin 1. -HFþ IC3 shows the placement for the 74LS245. The o - indicates pin 1. -HFþ IC4 shows the placement for the 74LS04. The o - indicates pin 1. -HFþ IC5 shows the placement for the old 74LS175. The o - indicates pin 1. -Card Map 25