-Paul G. Crumley -Information Technology Center -Carnegie-Mellon University -Pittsburgh, PA 15213 - PC-Jr Internal Diskette Drive -GContents -G Acknowledgements ....................................... 1 -G Introduction ........................................... 2 -G Requirements ........................................... 3 -G Description of Modification ............................ 4 -G Parts List ............................................. 5 -G Modification Instructions .............................. 8 -G Debugging Tips ........................................ 20 -G Card Map .............................................. 21 -G Feedback .............................................. 22 -Contents ii - Internal Use Only - PC-Jr Internal Diskette Drive -GE-ACKNOWLEDGEMENTSHF- -X-acto is a registered trademark of X-acto Corporation. -Radio Shack is a registered trademark of Tandy -Corporation. -, PC and PC-Jr are registered trademarks of -International Business Machines. -TEAC is a registered trademark of TEAC Corporation of -America. -Tandon is a registered trademark of Tandon Corporation. -Qume is a registered trademark of International Telephone -and Telegraph. -CDC is a registered trademark of Control Data Corporation. -Apple is a registered trademark of Apple Computer -Incorporated. -Atari is a registered trademark of Warner Communications -Incorporated. -Acknowledgements 1 - Internal Use Only - PC-Jr Internal Diskette Drive -GE-INTRODUCTIONHF- -This document provides a set of instructions for modifying -the PC-Jr Internal Diskette Drive Adapter to allow the -connection of a third diskette drive to the PC-Jr after a -second diskette drive has been added by following the -instructions presented in the document -" PC-Jr Internal Diskette Drive - Hardware Modification for Second Diskette Drive" -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 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 2 - Internal Use Only - PC-Jr Internal Diskette Drive -GE-REQUIREMENTSHF- -HFþ Hardware - HF- PC-Jr with a second diskette installed as described - in the above cited document. -HFþ Software - HF- DOS 2.1 - The software patches provided in this document will - only work with DOS 2.1. If you need to use some - higher level of DOS please contact me for - information on how to patch your software. - HF- A diskette with a copy of the file 3RDDISK.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 3 - Internal Use Only - PC-Jr Internal Diskette Drive -GE-DESCRIPTION OF MODIFICATIONHF- -By following this set of instructions you will make the -following modifications to the PC-Jr Diskette Drive -Adapter: -HFþ Alter the cable made when connecting the second - diskette drive so that a third diskette drive may be - connected. -HFþ Make a few connections to existing circuits on the - diskette adapter. No existing connections are altered, - only new connections are made. -HFþ Assemble the third 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 third - 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 and third diskette drives. -Unfortunately, in order for the BIOS to automatically know -about the existence of the second and third diskette -drives, 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 and -third diskette drives. Since the support for the -additional diskettes 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 4 - Internal Use Only - PC-Jr Internal Diskette Drive -GE-PARTS LISTHF- -The modification requires the following parts: -HFþ 4 ft Wire-Wrap wire. 30 or 32 gauge Wire-Wrap wire - works well for these connections. -HFþ 1 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 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) -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. -Parts List 5 - Internal Use Only - PC-Jr Internal Diskette Drive -HFþ a knife such as an X-acto modelling knife. -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. Electronics "supermarkets" such as -Radio Shack have a variety of soldering irons. Radio Shack -item number 64-2070, a 25 Watt soldering iron for about -$5.00, should be fine for this and other small projects. -If you go and buy a soldering iron don't forget solder. -The edge connectors should be available for a number of -companies. If the company that you decide buy the diskette -drive from does not sell the connectors you should be able -to find two at a Radio Shack or some similar electronics or -computer shop. -There are a number of companies that make PC compatible -drives. TEAC, Tandon, Qume, and CDC (Control Data -Corporation) 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 make sure that the enclosure and -power supply are fused and 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. - NOTE: -Parts List 6 - Internal Use Only - PC-Jr Internal Diskette Drive - I would discourage the use of home-built power supplies - for those that do not have a large amount of experience - with the design and construction of electronic - circuits. There are a number of safety issues that you - must be concerned with when constructing such a power - supply. In addition, there are some typographical - errors in the PC-Jr technical reference manual which - show incorrect power connections on the power supply - card. -Once all of this is collected you are ready to proceed. -Parts List 7 - Internal Use Only - PC-Jr Internal Diskette Drive -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 assumes you have already upgraded your -PC-Jr to a two diskette system using the instructions -provided in the document " PC-Jr Internal Diskette Drive --- Hardware Modification for Second Diskette Drive." If -you are adding the second and third diskette drives at the -same time you might wish to use the document " PC-Jr -Internal Diskette Drive -- Hardware Modification for Second -and/or Third Diskette Drive." This document is available -in the JRDISKS PACKAGE from CMUPGC at PGHVM1. -It is assumed that you have a copy of the first document -available as a reference while you are doing this -modification. You might like to read over the instructions -in the second diskette drive before you start this -modification to refresh your memory. -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. Modify diskette adapter card. - For review, remember that IC1 is the 7438 and IC2 is a - 74LS175. These two chips were installed when the - second diskette drive was installed. IC3 is a 74LS245 - that is already installed on the diskette adapter. A - connection was made to this chip when the second - diskette drive was installed. - No new chips need to be added to install the third - diskette drive. You will simply add wires to the - card. - HFa. Unplug the PC-Jr from the wall outlet, open the - case, and remove the diskette adapter from the - system. Simply disconnect the cable from the - diskette adapter and leave the internal diskette - drive and external diskette drive connected to the - cable for now. - HFb. Locate the 74LS245 at position IC3. Connect pin 16 - of IC3 to pin 5 of IC2, the 74LS175. You are now - done with IC3. -Modification Instructions 8 - Internal Use Only - PC-Jr Internal Diskette Drive - HFc. Connect pin 7 of IC2 to pins 9, 10, 12 & 13 of the - 7438 located at position IC1. You are now done - with IC2. - HFd. Cut two pieces of wire about 12 inches long. - Solder one end of one of these wires to pin 8 of - IC1 and solder one end of the other wire to pin 11 - of IC1. You are now done with IC1. - HFe. At this point all connections to the chips should - be completed. You have attached one new wire to - IC3, the 74LS245. This wire was attached right - next to the wire that was attached when the second - diskette drive was installed. You have attached - two new wires to IC2 and you have made connections - to 6 pins on IC1. - Each pin on IC1 should have some wire attached to - it while the following pins on IC2 should be - unused: - HFþ IC2 -- pins 3, 6, 10, 11, 12, 13, 14 & 15 - HFf. 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 ! - ! - 1 o 3 o 5 o 7 o o o o o o o o o o ! - ! - o o o o o o ! - ! - o o o o o o o o o o o o o o o ! - ! - HFg. 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 were used - when the second diskette drive was installed. We - are going to attach the signals needed for the - third diskette drive to the pins labeled 1 and 3 in - the above diagram. Connect one of the 12 inch - wires to pin 1 and connect the other to pin 3. It - doesn't matter which wire goes to 1 and which goes - to 3. What does matter is that you make the - connections to pins 1 and 3. 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 Instructions 9 - Internal Use Only - PC-Jr Internal Diskette Drive - modification. - HFh. 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. - HFi. Test that the adapter it is still operating - correctly as a two diskette adapter by installing - it in the PC-Jr and reattaching the cable that - leads to the internal and external diskette - drives. 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. -HF4. Alter the cable so that the third diskette drive can be - attached. - As before I am assuming you have done the modification - to attach a second diskette to the PC-Jr so I will now - go into great detail about how to "press" the - connectors on to the cable. - HFa. Once the diskette adapter has been tested turn off - the PC-Jr and the external diskette cabinet and - remove their power cords for the wall outlet. Now - remove the diskette cable so it can be modified to - accommodate the third diskette drive. - HFb. The cable should currently look something like - this: - __ __ - ! ! ! ! - _ ! ! ! ! - ! !----------!__!--------------------------------------<===>--!__! - ! ! - !_!<-- 8" -->! !<------------------- 2'-2" ----------------->! - HFc. The new connector will be installed near the end of - the cable. (see the diagram below) The exact - distance will have to be determined by you. Select - the distance so that the cable will easily fit onto - the two diskette drives when they are mounted in - the external enclosure. This new connector will - connect to the B: drive while the old connector -Modification Instructions 10 - Internal Use Only - PC-Jr Internal Diskette Drive - will become the new C: drive connector. - HFd. Once the correct distance has been determined - install the new connector on the cable. The twist - should be toward the center of the cable. The - cable between the new and endmost connector should - be flat. You may have to make the slits in the - cable a bit longer to allow the new connector to be - placed at the proper distance from the end of the - cable. Remember to keep the pin 1 identifiers - correct. The cable should now look like this: - __ -- __ - ! ! ! ! ! ! - _ ! ! ! ! ! ! - ! !----------!__!-----------------------------<===>--!__!-----!__! - ! ! - !_!<-- 8" -->!<------------- about 2' -------------->!<- 5" ->! - HFe. Now the signals that were placed on the cable by - making connections at the points shown as 1 and 3 - in the diagram used to modify the diskette adapter - must be connected to pins 12 and 16 of the endmost - connector. These signals are now on pins 2 and 6 - in the cable. - HFf. 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 isolate the - pin 2, 6, 12 and 16 conductors from the cable. Use - the modelling knife to separate these conductors - form the cable. - HFg. The conductors for pin 2 and pin 6 should be cut - off near the endmost connector while you should cut - the conductors for pin 12 and pin 16 near the new - connector. - HFh. Now you should solder the pin 2 conductor to the - pin 12 conductor and solder the pin 6 conductor to - the pin 16 conductor. The completed connection - should look something like this: - --- --- - ----------------------------! !--------------------------! ! - pin 1 ! ! ! ! - ! ! pin 2 =====\\ ==== ! ! - ! ! pin 6 ==\\ \\ ==== ! ! - ! ! \\ \\ ! ! - ! ! \\ \\ ! ! - ! ! pin 12 == \\ \\==== ! ! -Modification Instructions 11 - Internal Use Only - PC-Jr Internal Diskette Drive - ! ! pin 16 == \\======= ! ! - ! ! ! ! - ! ! ! ! - ! ! ! ! - ! ! ! ! - ! ! ! ! - ! ! ! ! - ! ! ! ! - pin 34 ! ! ! ! - ----------------------------! !--------------------------! ! - --- --- - HFi. When the wires are soldered wrap the exposed - conductors with electrical tape. Make sure any - exposed conductors are well covered with tape so - there is no possibility of these connections coming - in contact with any parts of the external enclosure - or the printed circuit cards on the diskette - drives. - NOTE: - I am currently looking for a better way to describe - this. Many of you will probably notice that by - using pins 2 and 6 we could do something similar to - what was done with the twisted cable to make the - signals attach to pins 12 and 16. - This will require an additional connector but will - make for a neater job. -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: - HFb. 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. - HFc. Set both of the new diskettes in front of you with - the printed circuit cards facing up. - HFd. Remove the terminating resistor packs from the - drives. These are small packages of resistors that - look like an integrated circuit chip. Usually - these parts are not the same color as the other - chips on the card. Common colors for the resistor - packs include white, orange, brown, blue and - yellow. Unfortunately, some are black in color - thus finding them can be a little difficult. There -Modification Instructions 12 - Internal Use Only - PC-Jr Internal Diskette Drive - are three other clues to finding these resistor - packs. First, these parts are almost always near - the edge connector where the cable attaches to the - diskette drive. Second, the resistor packs are - socketed. Third, they usually don't have part - numbers like 74XXXX. - Once these resistor packs are found (there is one - on each diskette drive) they should be removed by - simply sliding the blade of a small screwdriver - under the chip and gently prying it out of its - socket. - NOTE: - It is possible that you might get a diskette - drive that has no resistor packs in place. If - you got a used diskette drive the previous - owner may have removed the resistor pack. - Though it is very uncommon for a company to - ship new diskette drives without the resistor - packs installed it is possible. If you see an - empty socket near the edge connector and can - find no chip that looks like a good candidate - for being a resistor pack assume the resistor - pack has already been removed. - HFe. Set the diskette address jumpers to indicate the - diskette drive should respond to the DRIVE SELECT 1 - signal. Each diskette can be set up to respond to - one of 4 drive addresses. Most diskette - manufacturers label the jumpers on their drives - DS0, DS1, DS2 & DS3. You may wonder why you are - setting both drives to respond to the same - address. The cable is built so the proper signals - are directed to each drive so that all drives - should respond to the DS1 address. - Most drives that are advertised as being PC - compatible will already have the jumpers set up so - the drive will respond to DRIVE SELECT 1 and will - not require you to move any of the jumpers on the - drive. - NOTE: - It is unfortunate that there is no standard - method of implementing these DRIVE SELECT X - jumps on diskette drives. Many drives have - have nice, well labeled jumpers or switches - while others have no labels and the jumpers are - simply pieces of wire connecting pin positions - in standard chip sockets. I would recommend - talking to a technically oriented person at the - company where you are thinking about purchasing - the diskette drives before placing an order. -Modification Instructions 13 - Internal Use Only - PC-Jr Internal Diskette Drive - Make sure these jumpers are either well - labeled, preset to DRIVE SELECT 1, or well - documented in a manual that is shipped with the - drive. - HFf. Install the drives in the cabinet and connect the - power supply to the drives. Be careful that none - of the moving parts on the diskette drives will - come in contact with any of the mounting hardware - or cables in the cabinet. When the drives are - positioned such that they are not going to come in - contact with anything that would restrict their - operation fasten them in place so they will not - move. Make sure the diskette drive is securely - mounted so that the connections will be less likely - to vibrate loose with use. - HFg. Attach the cable to the diskette drives. The - connector at the end of the cable will be attached - to the drive that will be known as C: (this used to - be attached to B:) and the new connector will be - attached to B:. - HFh. 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. - HFi. 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. - HFj. Place the cable on the modified diskette adapter - card and insert the adapter card in the PC-Jr. - HFk. Attach the cable to the internal diskette drive. - HFl. Recheck these connections. - HFm. 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 and - third diskette drives' power supply into the wall - power outlet, turn on the new diskette drives, 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. -Modification Instructions 14 - Internal Use Only - PC-Jr Internal Diskette Drive - HFa. The DOS boot record must be altered so that BIOS - will be told that three 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 - 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 - 3RDDISK.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 - 3RDDISK.DBG you will have to enter the DEBUG - commands yourself. I will first describe how to - use the file 3RDDISK.DBG. - HF1) First, you must get the file 3RDDISK.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 - 3RDDISK.DBG will be shown as ('s and )'s - below.) -Modification Instructions 15 - Internal Use Only - PC-Jr Internal Diskette Drive - NOTE: - DEBUG uses square brackets. These - characters will be represented as - parenthesis in this document. - HF2) You must copy the file 3RDDISK.DBG to the new - DOS diskette in the same manner you copied - DEBUG.COM. Use the command "COPY B:3RDDISK.DBG - A: /V". - HF3) Next, use the command "DEBUG < 3RDDISK.DBG" to - run the DEBUG program. DEBUG will take all of - its commands from the file 3RDDISK.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),80 - 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 - 091A:19FB 49 DEC CX - 091A:19FC 42 INC DX - -A 19F8 - 091A:19F8 OR BYTE PTR (0410),80 - 091A:19FD JMP 1A26 - 091A:19FF - -N FORMAT3.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 FORMAT3 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. -Modification Instructions 16 - Internal Use Only - PC-Jr Internal Diskette Drive - 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),80 - JMP 012E - W 100 0 0 1 - N FORMAT.COM - L - U 19F8 L 5 - A 19F8 - OR BYTE PTR (0410),80 - JMP 1A26 - N FORMAT3.COM - W - Q - HF3) If this works correctly you have just made a - new DOS diskette. A new version of the FORMAT - command called FORMAT3 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 three 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. -Modification Instructions 17 - Internal Use Only - PC-Jr Internal Diskette Drive - 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 diskettes in their cabinet - then turn on the PC-Jr. After DOS boots you should - have the use of all three 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 added - diskette drives 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 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 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 does not have any - kinks or strange twists in it. If you must, - 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 drives. - HFþ Try not to block any ventilation slots when - routing the cables. - HFd. Well, this is the final test. Plug the added - diskette drives 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 -Modification Instructions 18 - Internal Use Only - PC-Jr Internal Diskette Drive - 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 19 - Internal Use Only - PC-Jr Internal Diskette Drive -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 -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 problem is that of a - solder bridge forming and shorting 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 or third drive connected. -HF3. If the second or third drives don't work try installing - the new drives as the internal drive. You don't have - to physically install the drives, just make the cable - connections. This should test the second and third - diskette drives. -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 or one of the resister packs was - not removed. -These tips should give you some idea of where to start -looking if you have a problem. -Debugging Tips 20 - Internal Use Only - 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 21 - Internal Use Only - PC-Jr Internal Diskette Drive