WSCART01@ULKYVX.BITNET (04/08/90)
>>I tried bumping my 520stfm up to 1meg the same way. Solder wick >>sockets and caps. I socketed and capped. Runs ok. Added DRAM, boots >>gets verticle lines and bombs. Serious bombs. So badly that it >>didn't even display them. Tried reboot. No luck. Added some resit >>ors to the resitor slotss next to the ram. Comes up ok but only >>recognizes the lower half of my memory. Sounds like a Cashigh and Caslow aren't connected > >I went through this a little while ago, with TWO STfm's I have at my workplace >and here's what has to be done.... > >Follow the New Bank of Ram down towards the front of the machine. You `should >find a chip just off to the right on the way down, U68 and it should be a >74LS11N chip. If it is missing, your going to have to get one, and place >it in there. >The Hitachi # is HD74LS11p >There are three resistors that are not soldered in also, I believe there the >ones that you have made referece to. #'s R71 / R72 / & R73, and should be >33 Ohms @ 2% tolerance. >You machine should boot, and recognize the second bank. >The pad that you are referencing to are for two or six set ROM's! There are >three of them, two by the Rom chips and one by the MMU (MCU) chip. There >labeled 256K and 1M (or 1 Meg). If you are not replacing your ROM's then >LEAVE THEM ALONE! >There is a place on the mother board to install a Blitter Socket and CHIP, >But seeing that I use TurboST, and I have seen blitter installed machines, >and due to the type of use i am using the machines for, I have no need for >the blitter, so I have not investigated installing this. Fact is that besides >the blitter, there was (on both machines) another chip that more than likely >has to be installed if you desire the blitter upgrade in. Like I said, I >don't have the need, so I just never went any farther, This is to true! There are two versions of the 520STFM that i know about. One, like the man said, has a blitter socket (which i recomend filling) but i have no real idea if this mod works and weither you need that Hitachi chip. (I believe you dont need it but that is from my guess work not from the man who actual did the upgrade and got it to work.) There is at least one other version of the 520STFM. One of which i have and just did the upgrade. Basical, it doesn't have a blitter socket in it. The upgrade is diffent from that of the above blitter version. Here's my story: What i found when i opened the case was 6 roms each stating mega TOS 1.2, 16 256k ramchips 120ns with a gap above each for another ram chip. Just to the left of these were a bank of 33 ohm resisters, a gap, another bank of resistors, 86ohm. NO BLITTER SOCKET! How i upgraded: Desolder the 16*16 holes put in sockets. (It is the wise thing to do.) Check RAS line to see if connect. I was so i moved on to the CAS lines. Neither CASHIGH nor CASlow (Pin 15 of memory chips) were connected. I searched but found no empty gaps to add resistors to! Trace with multimeter to confirm. CONFIRMED! Add line from MMU pin 22 (dot=1, counter clockwise is next higher pin, side goes from 26 to 10) which is the CAS1high, took a resistor and some wire and ran a lead from it to the high bank of memory (Left side as you type on it). Took a wire from MMU pin 21 (CAS1low) to resistor to low bank of memory (closes to MMU). That is it. (opps... put in memory) Maybe this will help the original poster. Stuart Carter | To the Gods at University Of Florida, University OF Louisville | Dear sirs, Physics Dept. | soon to be... | Please give me a teaching position. Stuart Carter | University of Florida | Truely, Astro Dept | Stuart Carter