27C801 + BJ3M-20 + 74LS139 Decoder - Black Screen!

hi guys,

i tried to built an som2 cart mod with BJ3M-20.

Used a 74LS139 decoder and swapbin method. Used 4 x 27C801 eproms.

Solder 2 on the front side and 2 on the backside and connect Eprom 1-4 to the 139 decoder

OR, VCC and GND are also set. A21 and A20 are currently connected to the solder points on the pcb.

Unfortunatly i got only a black screen. The ROM will recognized via U16, but after checksum check, the result is "BAD"

I read that A20 and A21 is GND on this pcb...

Could anyone advice how i have to connect the 74LS and A20/A21 Pins, so that it will work?!


Thanks

red

Update:



Solder direct to A20 from 74LS. Lift Pin 13 and connect LS Pin for A21 to it.



Now, that checksum is okay, but the rom has still black screen.



Dump the rom with Retrode and dump is also valid in snes9x but it is up to 60% different with the files which i have burned!



Thanks for advice



red

Are you swapping the pin 31 and 24 (I think it was 24) on the EPROMs? The swap bin isn't a standalone solution.

yes i swapped the pins and connect to the right pins on mad.

thanks

red

This is how your 139 should be connected

hi,

thanks

i connect a 100nF between +5V and GND. Same result. Burn again new chips with 27C801 and the on BJ3M-10.

Lift Pin 13 from mod and connect him to Cart 48. Connect A21 to Cartposition Pin 13 from Mad which is connected to Cartpin 46 -> Checksum is okay in U16.

Test all connection -> same /

Have anyone a other advice?!

thanks

red

Maybe your ordering of the roms is off.... my rom 1 is your rom 2 or whatever....
I've done this mod and it works fine.

Why are you lifting pin 13 and all that? you shouldn't have to move any traces or pins. just standard rom buss connections with a21 and a20 going to the LS139.

okay. Your cartmod with same pcb works fine?!

On Bj3M the A21 is on GND. Could you post a image of your working cartmod?!

The rompositions are completly correct. 1 is 1, 2 is 2, 3 is 3 and 4 is 4. Connected to LS139

I got a bad checksum from u16 when A21 was direct connected to Pin 13 of Mad-1.(without lifting the pin 13) and it doesn't work.

Lift Pin 13 and Solder A21 on PCB Pin 13 of Mad and connect lifted pin 13 direct to Cart 48. Checksum is ok.

Will test the pcb with only one tsop and same game. Will check the result.

Thanks

red

Test with tsop on same pcb type

Lift Mad Pin 13 and Pin A21 from TSOP.

Connect A21 to Mad-1 13 pin on backside of the pcb. The Game works, but it seems that he can't create a sram file.

Connect lifted pin 13 to A21 -> Black screen!
Connect lifted Pin 13 direct to Cart#46, -> same
Connect lifted Pin 13 direct to Cart#48, -> same

I have no idea what the issue here is! Hope anyone could help.

Connect the 4x 27C801 via LS139 decoder on the same way like the tsop-> still black screen.

Thanks

red

I think you are making this much harder than needed.

Connect A1-19 of the mask rom cart connections to A0-19 of your all your roms.
All 4 roms will all connect together. Same thing for D0-D7 and CE lines.

Then connect the OE lines (this is the only line you won't tie to all the other OE lines) and A21&20 and the 4 Roms OE lines just like the pic shows in my previous post.

You don't have to do anything with the mad1.

The only exception to this scheme is if you have a host cartridge that uses 32 pin mask rom.
The above instructions assumes you are dealing with cart that uses a 36 pin mask rom. And since you tested with a Tsop adapter, I assume you are working with a 36 pin mask rom cart.

In general, the cart solder pads are pretty fragile and maybe you have a broken trace to one (or more) of your pads.

It would help if we knew which cart you are working on (1J3M ??) and what game you are wanting to use/run on it.

Edit: I see, you are using a BJ3M and SOM2.

BJ3M is a 2 rom cart. Both roms are 36 pins.

The above instruction are for a single rom cartridge.
Her is a video of what you are wanting I think...
http://youtu.be/a_OEUKEEs_E
I don't know what you need to do to get the 2 rom cart to look to just 1 rom setup (1 rom x 4)
I think in other posts someone needed an OR circuit???? I may be wrong...

hi,

on one maskrom boards it works without any problems.

I have also built a som2 with 4x 27C801 on a 2 maskrom pcb from FF6. On this pcb it works without any problems or mad-1 modifications!

ok... Desolder all and built on other pcb! Damn!

thanks

red

Maybe you solved your issue.

Sorry but I didn't see this post until now.

For BJ3M pcb you only need to connect the A21 point in LS139 to MAD pin13 instead the A21 maskrom hole.

hi josete2k,

the problem was that i have thought the bin was soldered with swapbin patch, but i uses only split rom and this was the problem.



Thanks

red