How-To: Convert your NROM-128 to an NROM-256
by Low-Gain
Ever find it to be a pain in the ass to find the NROM-256 carts?
But have a bucket full of NROM-128's?
With just a few simple steps, you can make an NROM-128 into an NROM-256.
Modification Difficulty: Easy
Tools needed:
1 soldering iron
X-Acto Blade (or similar)
1 inch of 24awg wire or smaller
some soldering skills
Step 1: Look at the bottom of Both NROMs, 128 and 256 (if you have a 256 handy).
Note the similarities over all in part count, and lay out. There are 2 differences between the NROM-128 and the NROM-256, and they can easily go overlooked.
We're going to be looking at the solder side of the board (bottom). Focusing in on the PPG EPROM.
"nrom128 stock, note it lacks a trace going from pin 41 to Pin 27 on the PPG EPROM.
It is also connected to Pin 28 next to it which i believe is connected to the V+ Power plain which connects to Pin 37 on the edge connector. So that Pin is set to "high", we need to set it "low" by cutting the connects between pins 27 and 28 on the PPG EPROM"
"N-Rom 256 Stock"
Step 2: Note Pin 27 and 28 on the PPG EPROM are shorted together. I believe this to be V+ which would be pulling that port High. Anyways.. we want to use an X-acto blade to isolate pin 27 from 28. thus setting that port back to Low.
Step 3: Scrape the small amount of solder mask covering the extra pin length of pin 41 on the edge connector portion of the pcb. This will be our pad for soldering the jumper. Once clear, tin the now exposed "pad".
Step 4: Solder a jumper from Pin 27 of the PPG EPROM to Pin 41 on the edge connector. it is easier to Solder the jumper to Pin 27 first. then wrap the jumper between the EPROM pins for a straight length (reducing risk of melting insulation off the wired when soldering) then soldering it to Pin 41.
You're Modification should look something like this: (my soldering is a little messy due to the fact that it's late and i never work well with an iron past 11:30pm)
**Note: When making your jumper it's best to strip the insulation back a little more than needed on each end, tin the exposed wire, then trim back to a reasonable length. This will ensure a quick bond thus reducing the necessary head needed when soldering to the points of interest. **
As far as i know, that's all she wrote... I haven't had a chance to test this yet, but
i know this is what Alex Mauer does for his vegavox carts when needed. and it works. I just wanted to show ya that it's that easy and it makes life a lot easier
when looking for correct carts to use for burning your own EPROM's.
I will let Don (No Carrier) Explain the technical stuff since he's the wiz, not me.
For larger images, and a few more notes... visit the link below:
http://www.flickr.com/photos/lameboymus … 982863255/
Video and a better explained tutorial (more picture of steps) will be up soon on my website.
Good luck!
Post pictures of your success!
As usual.. let me know if there are any errors so that I may fix them. Thanks!