**************************************************************************  THE OBESE AGNUS,THE NEW 500 BOARD AND OTHER RECENT EXPERIENCES. `````````````````````````````''''''''''''''''''''''''''''''''''   By Andrew Wilson 23/07/89. WARNING.. ANY MODIFICATIONS MENTIONED IN THIS ARTICLE SHOULD ONLY BE DONE BY TECHNICALLY COMPETENT PERSONNEL: TECHNICIANS ETC.(not engineers) AS REPAIRS TO THESE MACHINES ARE COSTLY AND SERIOUS DAMAGE EASILY DONE.THE REMOVAL OF PLCC CHIPS (A500 AGNUS) FROM THEIR SOCKETS WITHOUT THE PROPER TOOLS IS PARTICULARLY HAZARDOUS. MOST OF THESE MODIFICATIONS REQUIRE GOOD SOLDERING SKILLS ETC. ALL WORK SHOULD BE CARRIED OUT AT AN ANTISTATIC WORK STATION. STATIC DOES EXIST, IT IS NOT A FAIRY STORY PUT OUT BY 3M CORP. TO SELL THEIR ANTISTATIC GEAR. SEE ANTISTATIC WARNING ELSEWHERE IN THIS SECTION. ALL POSSIBLE CARE HAS BEEN TAKEN IN PREPARING THESE NOTES BUT ANY MODIFICATIONS ARE DONE ENTIRELY AT YOUR OWN RISK. All modifications stated as fact have been done by me, mods put up as possibilities are my thoughts on a subject and have not been tried.  |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||  [Ed: Andrew is the brains behind the original Proton Ram boards, which are still valued very highly by their owners. He is now running his own Amiga-specific hardware manufacturing business (on a human scale, with human scale prices, too) and it may not be an exaggeration to say that there is little he doesn't know about the Amiga in general, and hardware specifically. He provides numerous products for all models of the Amiga, including 8-meg Ram boards, hard disks, digitisers, real-time clocks, and many other products. You'll see below that he really knows what he's talking about, and he's always been available to me when I have a hardware problem. He can be contacted at: 2 Meredyth St, Millswood 5034. With the expert help of Mario Nicotra, this mod was done to my early (Rev. 5A) A500, and it worked fine - the business of the switch from NTSC to PAL screens was done by bending the socket of pin 41 of the Agnes chip, perhaps the easiest of the alter- natives mentioned by Andrew. Note also that the full details required are here: all the docs from the US and even from Commodore here tend to forget to show you how to make the change from NTSC to PAL...  ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||| IN THIS INSTALLMENT ------------------ The Obese Agnus Chip Obese Agnus Software Compatibility Fitting the Obese Agnus to the REV5 A500 (Original 500) The New REV6A A500 Board The Different Types of A500s and Identifying Them [ED: 2000 Modification follows at bottom]   The Obese Agnus Chip. --------------------- The Obese Agnus Chip (8372A or 318069-02) is the new Agnus chip capable of addressing 1 MegaByte of Chip Ram on the A500 or B2000. This allows you to have more than TWICE as many windows and screens open than is possible with a standard Fat Agnus equipped machine. If opening twice as many screens and windows isn't your thing then it also means that the Hi-res modes of such programs as Digiview, DeluxePaint and others which refuse to run until all extra drives, windows, screens are closed will now open and also allow you to run extra flip screens etc. Games such as Boulderdash/Emerald Mines which refuse to load unless all external drives are disconnected are now much happier as well. Commodore is now shipping the Obese Agnus in most of the current A500s (without telling anybody) although Commodore in the USA will admit to it when questioned. These A500s are set up in Fat Agnus Mode so that even if an A501 board is plugged into them no improvement is obtained without further internal modification.  Obese Agnus Software Compatibility. ----------------------------------- Already 1 animation package (VideoFX 3D I believe) has been found which will not run with the 8372A in either Fat or Obese mode. This is a problem caused by the programmer reading or writing to registers in the Agnus chip in an illegal (non-Commodore approved) manner and may (should) be fixed in later releases of the package. CHECK that any software that you HAVE to use works with ONE Meg of Chip Ram before committing to this upgrade. All other programs tried so far, about 150, have been completely compatible.  Fitting the Obese Agnus to Early A500s.(REV5 Boards) --------------------------------------- Contrary to a message appearing on many local Bulletin boards it is not necessary to have the new Rev 6A board to fit the Obese Agnus to an A500. The 8372A can be fitted to the older Rev 5 boards simply by doing the following : 1 Remove the Fat Agnus 8371 from its socket (see warning above). Check orientation of pin 1 to facilitate installation of 8372A. Pin 41 of the Agnus socket which is earthed on all REV5 boards controls whether the A500 starts up in NTSC or PAL mode. When it is earthed the Obese Agnus initialises in NTSC Mode which means that all USA owners need to do is plug in the chip and they are in the correct mode. We on the other hand have to de-solder and remove the socket from the board to isolate pin 41 which is connected to earth on both sides of the board. This chip was designed in the USA!! Removing the socket is a difficult and laborious task so other methods of isolating pin 41 are possible. I DO NOT recommend trying to drill through the board as the two pins 41 and 42 are very close together, the trace between them is thick and there are thin tracks either side of it under the socket on the top of the board. Bending the contact on the socket is a possibility but make sure you get it right or you'll be removing the socket anyway. Placing a thin piece of hard plastic, eg mylar, between the pin and the contact is another possibility. By putting a SPST toggleswitch between pin 41 and earth it is possible to switch between NTSC and PAL on resetting the machine. This would give good compatibility with American software and for this reason and others DO NOT just break or cut pin 41 off the chip. Pin 41 is taken to a jumper pad on REV6A boards. 1 1 8 8 8 8 8 7 7 7 7 7 1 0 9 8 7 6 5 4 3 2 1 4 3 2 1 0 9 8 7 6 5 BEVELED CORNER | | | | | | | | | | | | | | | | | | | | | /ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ| 12 -| ¤ |- 74 13 -| ^ |- 73 14 -| | |- 72 15 -| INDENT FOR PIN 1 |- 71 16 -| |- 70 17 -| |- 69 18 -| |- 68 19 -| |- 67 20 -| 8372A |- 66 21 -| |- 65 22 -| |- 64 23 -| TOP VIEW |- 63 24 -| |- 62 25 -| |- 61 26 -| |- 60 27 -| |- 59 28 -| |- 58 29 -| |- 57 30 -| |- 56 31 -| |- 55 32 -| |- 54 |____________________________________________| | | | | | | | | | | | | | | | | | | | | | 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 5 5 5 5 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 2 Insert the Obese Agnus 8372A into the socket paying particular attention to the orientation. Pin #1 is located in the centre of the side immediately clockwise from the beveled corner of the chip and is marked by a small dimple. The 8372A should be installed with pin 1 to the front of the socket. This is marked by a large 1 on the silkscreening on the circuit board just above the words "FAT AGNUS". I overstress this point because this is an expensive chip and a wrongly inserted chip which has had power applied to it probably has a value of 0000 dollars. The socket on the REV6A boards has been rotated 90 degrees anticlockwise. BE WARNED!! 3 Locate the jumper JP2 on the circuit board to the right of the 68000 chip. Cut the trace between the centre and lower pads carefully with a sharp knife. Join the centre and upper pads with a small piece of light wire. This jumper changes the address of the A501 board or equivalent from C00000H to 080000H to make it contiguous with the first 512K of memory to give a 1MEG block of chip ram. The three pads of JP2 can be wired to a SPDT toggleswitch to allow changing from one memory location to the other if there is any software incompatibility with the new setup. 4 Pin 32 of the GARY chip (located above right of the Agnus socket) must be open circuit for this upgrade to work. This pin is the *EXRAM signal which is normally earthed by the A501 board when it is plugged into the A500. Several methods of achieving this are available as follows: a. If you have installed one of my A501 memory disable switches or other similar modification which open circuits pin 32 of the A501 memory expansion connector then this will serve the purpose. Leave it in the OFF position and disregard the rest of section 4. b. Locate the GARY chip and remove from its socket. Locate pin 32 and CAREFULLY bend it slightly outwards so that when GARY is put back in its socket pin 32 does not go into its socket. Return the GARY chip to the socket making sure that it is correctly positioned ie. pin 1 and notch to the right hand side. Pin 32 can be connected through a SPST toggleswitch to earth to preserve compatability with the Fat Agnus. Notch in end of chip | V _________________ Pin numbers > 1 -| o \_/ |- 48 2 -| |- 47 3 -| |- 46 4 -| |- 45 5 -| |- 44 6 -| |- 43 7 -| |- 42 8 -| |- 41 9 -| |- 40 10 -| |- 39 11 -| |- 38 12 -| |- 37 13 -| |- 36 14 -| GARY |- 35 15 -| |- 34 16 -| 5719 |- 33 17 -| |- 32 < Pin to be bent in 4b. 18 -| |- 31 19 -| |- 30 20 -| |- 29 21 -| |- 28 22 -| |- 27 23 -| |- 26 24 -| |- 25 ----------------- ******* ALL DUAL INLINE PACKAGE INTEGRATED CIRCUITS ARE NUMBERED IN THE SAME MANNER, ONLY THE NUMBER OF PINS VARIES. 5 Check all work done in all previous stages, and if everything is correct connect it to power supply, mouse and monitor and turn on the power. If it does not boot up as normal power off immediately and recheck. The longer the power is switched on with a fault the greater the damage. Check for bent or folded pins on GARY if you have had him out. If you have the disk drive disconnected or wrongly connected it will take a lot longer before the hand and disk appear on the screen. 6 Once you have booted successfully run PERFMON from the TOOLS drawer of the EXTRAS Disk [Ed: or PopInfo from MD11]. It should show 1MEG of Chip Ram and no Fast Ram on a 1MEG A500. Now try loading a picture, The Tiger on Megadisc 5 is most suitable, repeatedly. It should be possible to load more than twice as many as before (about 8 as against 3 I think from memory).  The NEW REV6A 500 Board. ------------------------ This board has been shipped by Commodore for approx. 2 to 3 months. The main reason for the change has been to allow Commodore to use the newer 1 Megabit chips and to allow for 1 megabyte of memory on the main board. This means that the A501 board is no longer needed if the extra 512K is installed on the main board. Current cost of this upgrade is approximately $160.00 . If the Real Time Clock is needed then clock boards plugging into the A501 slot are available for $50-60. There is provision for several resistor packs on the board although they are not fitted and their use is not clear. The change has little to do with the Obese Agnus upgrade although it is a little easier to fit to a REV6A board. The board also contains several new jumper pads, details of which are given below. REV5 BOARD REV6A BOARD APPARENT USE JP1 Yes Yes Connects 555 reset timer to main reset JP2 yes yes Maps A501 @ C00000 or 080000 JP3 yes yes Swaps *CAS of 512k banks of RAM JP4 no yes PAL or NTSC via pin 41 of Obese AGNUS JP5 no yes 28MHz CLK, XCLK and XCLKEN to AGNUS JP6 no yes 7MHz clock on pin 7 of 86way Exp Connector JP7A no yes Controls *EXRAM to GARY JP7B no yes CIA TICK from VSYNC or pin 32 of A501 JP8 no yes LPEN from FIRE0 or FIRE1 JP9 no no? J910A no yes Connects AUDIN to pin 18 of RS232 Port JP10B no yes Connects AUDOUT to pin 11 of RS232 Port JP11 no yes Connects CSYNC to BCSYNC or Video Hybrid (A Week Later) As can be seen from the above table most of these new jumpers are for convenience and do not represent radical improvements over the previous board. Conversion of a REV6A board to work with Obese Agnus is fairly simply and will be covered in a later article which will also cover fitting the extra 512K of RAM to the main board.  The Different Types of A500s and Identifying Them. --------------------------------------------------- This section does not attempt to identify the different types of disk drives, keyboards etc. which, particularly in the case of the A500, seem to change almost weekly. The A500. The base model of the range which, contrary to what B2000 salesman say, is expandable to Approx. 15 Meg of RAM, Hard Drives, etc. Somewhat limited power supply so a larger one is needed for hard drives. There are two basic types : A. The original REV5 board supplied from the beginning up until early 1989. Requires the A501 Board or equivalent for expansion to 1 Meg and use of Obese Agnus. B. The new REV6A board supplied from April/May 1989 on. The way to recognise it is to check the expansion bus connector on the left hand side of the computer. You'll notice that the early model A500 has a "fat finger" metal strip at the back end of the connector - the new A500 doesn't, instead it has two thin "fingers", ie, 2 metal strips in the corresponding place, of the same width as the rest of the strips of the connector. More on this and other related matters in the next issue. 2000 MODIFICATION Ed: The modification for the A2000 is pretty similar, and has been done by Mario (mentioned above) on a very souped-up system. Keeping in mind all the warnings and hints above, it goes like this: A. Remove computer cover, floppy cable (noting position of the red wire on the cable), power plug from connectror CN400, and power supply and drive assembly from the main unit. B. Remove the old slimmer Agnes as above, preferably using a chip extractor. Insert the new chip with the right alignment. C. Find Jumper J101 located on the lower right side of the power connector CN400, and consists of 3 posts - 2 of the posts are shorted together using a shorting block. Remove the shorting block and move it to the left, towards the power connector. For further info, see Page 13 of the A2000 system schematics - this jumper will enable address line 19 from the 68000 which controls the 1 meg address range. D. Locate and cut Jumper pad J500 (to the lower left of the 8520 at U301). This is a 2-pad jumper with a trace connecting the two pads. See Page 9 of the A2000 system schematics - cutting this trace keeps the _EXRAM signal from being tied to ground. E. Finally, to enable PAL rather than NTSC - locate and cut J102, NOT J201 as suggested in some docs. This is the equivalent of bending pin 41 of Agnes in the A500 mod. The mod is now finished, so re-assemble the unit, power up and hope for the best! And don't attempt it unless, as mentioned above, you're very adept at electronics hacking. Show these docs to such a person, however, and there should be little difficulty.  |||||||||||||||||||||||||| END OF ONE_MEG_AGNES ||||||||||||||||||||  WARNING - HANDLING MOS INTEGRATED CIRCUITS ------------------------------------------ These devices are static sensitive, and are easily destroyed by static charges built up by walking on carpet, rubbing on clothing, cats, etc. When working on equipment using these devices, always touch the metal frame of the equipment before touching any I.C.s, circuit boards, etc. If you have an anti-static wrist strap (available at Tandy), wear it. If not, retouch the metal frame occasionally to prevent any further buildup caused by your movements. If passing static sensitive devices to other people, establish skin contact before handing over the device. Touch the surface you are going to place an I.C. on before placing the I.C. on it. Place chips only on conductive surfaces eg. Aluminium foil, RF shielding, etc. The foregoing also applies to connecting peripherals to the Amiga. Touch the metal frames of both before joining them together. TREAT ALL I.C.s AS STATIC SENSITIVE DEVICES!!!!!