nesdev.org

Hi,

I read on this post http://nesdev.com/bbs/viewtopic.php?t=4 ... c&start=15 that sdm managed to make home-made RAM for his Game Doctor SF6 using some cheap PC RAM. I have some extra PC RAM lying around and was wondering how I could make some RAM for my Game Doctor SF7. I would like to make two 64mbit modules to have 128mbits total. I bought it bundled with 32mbits from Tototek a while back and accidentally fried the RAM. I don't really want to have to order more RAM from Tototek because it is expensive and takes a while to ship from Hong Kong. I'm not a huge electronics buff, but I am learning how these things work.

You need 4M x 4 bit 60ns asynchronous DRAMs which can be found on 72 pin SIMMs.

Ok, I have four 72pin SIMMs. One is a Kingston, one is PNY and the other two are generic vendors. The Kingston module has Toshiba TC514400ASJ-80 RAM, the PNY module has TI TMS44400DJ RAM, and the other two modules have LGS GM71C17403CJ6 RAM. Of the three types, I think that I will use the LGS GM71C17403CJ6 because the datasheet specifies it as 4MB x 4 bit 60ns. Also, what is the best way to remove surface mount chips? I tried using a soldering iron and utility knife, but it just ended up mangling the pins. I tried this technique on some old 30pin SIMMs as to preserve my 72pin SIMMs.

I'm told that a blow dryer (for hair) works quite well in this situation. Apply to the back of the PCB. Pretty much all the solder on the entire board liquefies, and surface-mounted DRAM will either drop right off or (if pinned) can be wiggled out with a pair of pliers with ease.

I think you're gonna need something with more power then a blow dryer. A paint stripper should work.

Yeah, a heat gun (I've seen those as cheap as $10).

There is also this stuff called Chipquik, solder that stays molten much longer. That could involve more cleanup and stuff though.

Thanks for the tips. I will see what I can find at Radio Shack tomorrow and let you know how things work out.

Sadly, I accidentally broke some of the pads off the GDSF7 RAM module when removing the fried RAM. I do not feel like tracing through the ripped pads to try and make a hack fix so I think I'll just order some 64Mbit RAM modules from Tototek.

I thought maybe I'd save some money by making my own RAM, but it turns out my soldering skills aren't quite as sophisticated as I'd like them to be. I was able to remove the RAM from the SIMMs no problem, but removing the fried RAM from the GDSF7 module was difficult. Also, I tried soldering some of the new RAM to the board, but didn't do a very clean job. The solder was all melded together making all of the pins connected. I can improve my skills with time, but for now, I'll just take the easy route.

Did you use flux? I find it helpful to have flux in a liquid form (flux pin). To remove excess solder, I've found that it's usually enough to add a bunch of flux, then carefully drag the iron across all the pins. The extra solder should form a ball that the iron can kinda drag along. Also helps to hold the board at an angle so gravity will help. You can tap the board on something (upside down) to drip it off. Can use solder-wick (aka solder-braid) first, if there is a huge amount of solder. The flux makes everything easier. I know you're done with it, but just so you know for next time.