From: Thomas Weeks To: Dieter Kedrowitsch Date: Thu, 02 Feb 1978 00:40:38 +0500 Subject: Re: A500 JP2 Around 20-Nov-97, Dieter Kedrowitsch typed: >Hi, I have a quick question. >On my A500, Jumper JP2, the one next to the processor is missing the middle >pad. There is only 1st and 3rd pad there. I need to jump 1 and 2. Do you know >were this trace leads to? I need to enable address line A19. That center pad ISn the agnus' A19 input... ping 59 onthe Agnus... If you have (as I suspect) the old rev 5 motherboard... your agnus will look like this: --------------- --u-- Pin 59 | | | | A19->| | | | | 8372 | | | | | | | | | | | | | | | | | | | =============== | | ^ X | | 1 X | | X | | ^ | | | ----- | JP2 Where the 1 is pin one (in middle of taperd edge) and A19 in pin 59 (6th pin down from upper left hand edge of chip). Someone has worked on your motherboard in the past and overheated and lifted that center JP2/A19 pad (don't fret if you bought it new... I have seen "new mobo's" before from Commodore that were obviously refurbs...). There are a couple ways of fixing this: 1) EASY WAY: simply take an exacto knife and CAREFULLY scratch the trace that used to GO to the center pad removing the green motherboard insulation back thus exposing about about 1/2" of the raw copper trace. Lightly tin it with a soldering iron being careful not to over heat it (it too will lift). After you can see that the color has changed from copper to silver color, strip and tin a small piece of wire wrap wire, bus wire, or even a bit of paper clip (!?! been there done that!) and align almost 1/2" of it with the newly exposed and tinned mobo trace. Simply touch the wire onto the trace with the tinned (and wet (solder)) tip of the iron and you will have a fairly good "solder only" trace fix. now just solder the other end to the appropriate pad (up for 512k, down for 1M of CHIP RAM) and you should be set. 2) DIRECT AND MORE DANGEROU WAY: **VERIFY THAT YOU TRUELY HAVE A SINLGE LAYER MOTHER BOARD BEFORE CHOOSING THIS STEP!!** Find a space next to the ROM socket and JP2 with no traces on either side of the mother board and drill a small (wire sized) hole through to the other side (drilling through a ground plane is ok... but just be sure you insulator "reaches" all the way through and past the exposed ground plane!) NOTE: Don't drill the hold TOO close to the JP2.. it'll just be a pain. Find pin 59 as show in the illustration above, but on the BACK side of the mobo. Be sure you don't get flipped-around syndrome.. it's easy (and DANGEROUS) to make this mistake! Strip, and tin the wire and feed it through the hole (front to back side). Solder the wire wrap wire to pin 59. Cut the wire on the front side to reach the pad, tin it, and solder it to which ever solder pad you need to use (again... 512k on the upper pad and 1M Chip RAM on the lower). Don't forget.. that you will need to sever the _EX_RAM line (pin 32 on the trap door pine assembly) going to the trap door slot (A510 RAM) depending on what CHIP RAM jumer you selected to jumper the agnus to. If you chose 1M mode, then cut the _EX_RAM line going to the trap door slot... leave it in tact if 512k is desired... (A dremel does a very nice job of cutting traces like this...) And before you ask... YES.. a single DPDT switch CAN be used to switch modes.. But I ONLYn recommend doing so with the power off and be sure to have pleanty of debouning R/C in there... but this really is not a very useful hack because VERY few games and the like are not compat with 1M chip RAM... and even still they're kind old anyway.. well.. the whole MACHINE is anceint I guess! heehe... hmm.. And yet I'mn still using one to write you this email! hehe ;v) Anyway.. hope all this helps.. and DON'T try these mods if you are no good with a soldering iron... I have seen MORE people try this and end up scarring and marring their mobo's than with any other Amiga mod. If worse comes to worse... take it to a music repair shop (because TODAYS PC tech's don't know how to solder.. they just swap cards! They would probably burn themselves and then SUE you! heh). Draw the sound tech a picture of what you need done... I have worked in SEVERAL pro audio tech shops and the lowest tech there will ALWAYS more competent than your top 20% of todays self proclaimed "PC techs". There are usually pretty good techs in such places (good analog troubleshooting skills and soldering and the like)... anyway... Hope this all helps you out... Think I might go ahead and make up a Tom D Tek Tech Tip out of this one... L8ER! Tom D Tek -- __________________________________________________________________________ / Thomas W. Weeks |Team AMIGA Commodore Amiga 500/030 40MHz \ | A&M EET/Telecom Grad '95 | /// Hacked Into Black Tower Case, | | Authorized Amiga Tech (7yrs) | __ /// 9M RAM, SyQuest 44M, 700M-o-SCSI | | Contact Me @ | \\\/// IBM 286 Hardware Emulator, | | o------------o | \XX/ Home Brew Audio A/D, HP48GX | | Email: tweeks@texas.net |"Amiga, The Computer for the Creative Mind"TM| |Web:lonestar.texas.net/~tweeks|"Mac, The Computer for the Rest of Us"TM | \_____________________________|____________________________________________/