SOLVED: How to Increase SRAM on an SA1 Board?

A place that you can discuss reproduction of classic titles or "licensed-for-reproduction" homebrew for personal use.

Moderators: B00daW, Moderators

Forum rules
1. NO BLATANT PIRACY. This includes reproducing homebrew less than 10 years old, with the exception of free software.
2. No advertising your reproductions, with the exception of free software.
3. Be nice. See RFC 1855 if you aren't sure what this means.
Post Reply
X2Whiskey
Posts: 4
Joined: Wed Aug 14, 2019 4:04 pm

SOLVED: How to Increase SRAM on an SA1 Board?

Post by X2Whiskey » Wed Aug 14, 2019 4:59 pm

Hello,

I'm looking to convert the 256 kbit SRAM on a SHVC-1L5B-20 PCB to 1 Mbit SRAM and am looking for some direction. When comparing chip pinouts, I see the 256Kb is 28 pins while the 1Mb is 32 pins. I also see that pin 28 of the 256 (VCC) conflicts with pin 30 of the 1Mb (CE2). Does that mean I should isolate pin 30 (CE2) of the 1Mb? And where should I route that pin connection to?

Since seeing Voultar's Video https://www.youtube.com/watch?v=ImH8B1cG3p0 on YT, I have on a personal quest to make my own Gradius III reproduction incorporated with Vitor Vilela's SA1 enhancement hack https://github.com/VitorVilela7/SA1-Root. Unfortunately, I think think that video has a lot of misleading information which I think is odd considering the author's reputation and experience.

So, I've identified a suitable donor PCB from the Japanese Super Famicom game Mini Yonku Shining Scorpion https://www.pricecharting.com/game/supe ... g-scorpion. It comes with the SHVC-1L5B-20 revision PCB that has a SOP-28 256 kbit SRAM, and solder mask-covered pads allowing for the mounting of a larger SOP-32 SRAM. Oh, and this cart can be had for under $10 shipped from Japan through EBay.
Last edited by X2Whiskey on Fri Aug 16, 2019 4:31 am, edited 1 time in total.

Ice Man
Posts: 394
Joined: Fri Jul 04, 2014 2:34 pm

Re: How to Increase SRAM on an SA1 Board?

Post by Ice Man » Thu Aug 15, 2019 4:37 am

I just build a Gradius III on SA-1 but using a SHVC-1L3B-10 PCB instead.

For SHVC-1L5B-XX PCB just solder it in as is since CE2 is tied VCC afaik.
Attachments
sram-gradius.png

X2Whiskey
Posts: 4
Joined: Wed Aug 14, 2019 4:04 pm

Re: How to Increase SRAM on an SA1 Board?

Post by X2Whiskey » Thu Aug 15, 2019 6:28 am

Thank you for the input.

I just spent some time looking up and comparing SRAM datasheets as well as doing some pinout tracing on the SHVC-1L5B-20. The notes I've taken so far are in the attached image. Everything seems to correlate to what you've said, but I see one inconsistency. The 1Mb SRAM datasheet denotes pin 1 as NC (Not Connected), but the SHVC-1L5B-20 has that pin pad hardwired to the SA1's pin 104.

Should the 1Mb SRAM pin 1 be left floating?
Attachments
SA1 SRAM Upgrade Notes.jpg

Ice Man
Posts: 394
Joined: Fri Jul 04, 2014 2:34 pm

Re: How to Increase SRAM on an SA1 Board?

Post by Ice Man » Thu Aug 15, 2019 9:50 am

NC means internally not connected. It does not matter where you connect that pin or leave it floating. It won't do anything at all.

X2Whiskey
Posts: 4
Joined: Wed Aug 14, 2019 4:04 pm

Re: How to Increase SRAM on an SA1 Board?

Post by X2Whiskey » Fri Aug 16, 2019 4:30 am

So to wrap things up: I cleaned the solder mask from the PCB's extra traces and soldered in the 1Mb SRAM with no special trace cutting or rewiring and all is working fine. Hopefully this proves useful for others having the same questions.

pausuri
Posts: 4
Joined: Wed Oct 02, 2019 2:24 pm

Re: SOLVED: How to Increase SRAM on an SA1 Board?

Post by pausuri » Mon Oct 07, 2019 2:40 pm

X2Whiskey wrote:So to wrap things up: I cleaned the solder mask from the PCB's extra traces and soldered in the 1Mb SRAM with no special trace cutting or rewiring and all is working fine. Hopefully this proves useful for others having the same questions.
That's really good that you managed to sort it out.
I want to do the same, can I have a link to buy the 1 Mbit SRAM spare part??

If is it not much trouble, could you upload a picture of the pcb with the fitted new ram??

I really appreciate it!!

Thanks

Post Reply