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View topic - SMS2 Chip Info, Late Board 171-6395A

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  • Joined: 14 Jan 2024
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SMS2 Chip Info, Late Board 171-6395A
Post Posted: Fri Jun 14, 2024 10:39 am
Heya Guys,

I am hoping you knowledgeable lot might be able to help me.

I have been working on a project where I need to rebuild a SMS mainboard and re-use the custom chips.

I have ran into an issue where all the schematic I have found online are not quite right, my board has two chips which I am struggling to find info for:

IC10 (IC2 on older boards) MPR-15155 (23pin 2mbit mask rom)
From what I can find online it should have the same pinout as the 28 pin variants on other models but tracing some of the data lines and they go do completely different places so I am suspecting the pinout of this chip is totally different to the regularly found 28 pin versions.

I was able to read the contents of this chip by selecting 27C020 in my programmer but I am not sure this process uses all the pins and I may have got lucky.

IC3 is a Sanyo LC3664RL
Can I assume this has the same pinout as the other 4168C's that the board has two of as the older revisions have one of these chips here.

I am hoping someone can help shed some light on this.

I really appreciate any info anyone can give me here.
1718361486192 (Large).jpg (439.8 KB)
Mainboard
1718361486192 (Large).jpg

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  • Joined: 30 Sep 2023
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Post Posted: Fri Jun 14, 2024 1:13 pm
Check the pinout here

https://www.smspower.org/Development/BIOSReplacement
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  • Joined: 14 Aug 2000
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  • Location: Adelaide, Australia
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SMS2 Chip Info, Late Board 171-6395A
Post Posted: Fri Jun 14, 2024 1:13 pm
The PROM pinout is here (no time to search the forums or trace it out?)
https://www.smspower.org/forums/post116604

The Sanyo LC3664 has the standard 8Kx8 SRAM pinout. The only difference in pinout between the LC3664 and the 4168 is the 4168 has REFRESH on pin 1 where as it's N.C. on 8Kx8 SRAM.

Hope that helps.
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  • Joined: 14 Jan 2024
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Post Posted: Sat Jun 15, 2024 8:06 am
Amazing! thank you guys!

I was digging high and low for info as I couldnt match the rom to anything that brought up any search results as I wasnt even sure what it really was as all I could find was the 28 pin version.

Also thanks for confirming about the sanyo ship, so from what I can tell I can directly swap this with the nec versions?

I also noticed many of the pinouts on these chips are totally different to the schematics I have found so not sure what is going on there. I will have to manually pin out the whole board I think.
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  • Joined: 14 Aug 2000
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SMS2 Chip Info, Late Board 171-6395A
Post Posted: Sat Jun 15, 2024 1:32 pm
bonkas wrote
I also noticed many of the pinouts on these chips are totally different to the schematics I have found so not sure what is going on there. I will have to manually pin out the whole board I think.


Going by the photo, the board you have is a PAL Master System 2 with the later chipset. It should match the schematics here:

https://www.smspower.org/Development/SegaMasterSystemIIServiceManual

Is this a personal project or part of a school/college/university course or something?
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  • Joined: 30 Jan 2007
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Post Posted: Sat Jun 15, 2024 11:11 pm
bonkas wrote
I also noticed many of the pinouts on these chips are totally different to the schematics I have found so not sure what is going on there. I will have to manually pin out the whole board I think.


What schematics are you looking at? The PAL 2M board is largely the same as the earlier PAL revision except that it has the MB3514 encoder and a two megabit BIOS ROM. The rest of the chips are exactly the same.
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  • Joined: 14 Jan 2024
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Post Posted: Sat Jun 15, 2024 11:58 pm
ApolloBoy wrote
bonkas wrote
I also noticed many of the pinouts on these chips are totally different to the schematics I have found so not sure what is going on there. I will have to manually pin out the whole board I think.


What schematics are you looking at? The PAL 2M board is largely the same as the earlier PAL revision except that it has the MB3514 encoder and a two megabit BIOS ROM. The rest of the chips are exactly the same.


Yeah this i exactly why I am confused. for an example, I just took another quick look at the schematic and my board.

If you look at IC3 and pin 20 which is CE but has a label CE1, according to the schematic the only path for this pin to go is to the cartridge connector if I am understanding the schematic correctly but the connector doesnt have this connection, only CE3 which it does not go here.. It infact goes to Pin 29 of IC4 which is CE0.

The other funny thing is if I take pin 10 (A0) of IC2 (IC10 on my board), according to the schematic this should go to pin 25 on the cartridge connector but instead goes to pin 27 on the connector which is A2. EDIT: I just realised I am comparing the pinout to the 28 pin chip and not 32pin chip that I have.

It was at this point I decided to give up and attempt to manually pin everything out. Maybe I am just reading the schematics wrong?

The other question I have around the schematic (and I may be thinking too much into this!) is that if there is a number of A0 on a bus, the connection may not be connected to all chips on the bus as the pins seem to "enter" and "leave" the bus connection via a diagonal line, I am assuming for example if reading from left to right if I saw -----------/________ the connection does not go from the left side to the right side but it was ----------\_________ then reading from left to right the pin must follow in that direction? and in cases where I see ----------\/---------- I beleive the connection must go to two places.

This is just a personal project for myself and a group of friend to accomplish two things:

1. Can I do it? Improve my PCB design skills as I only have a few designs under my belt.
2. If the above is successful can I implement the mods into the PCB design to fit in to a sega chassis.

So I guess the main question now is after getting more info from you guys on my board differences, am I reading the schematic correctly?

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