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[Solved] Help with Aladdin repro

Posted: Mon Jul 06, 2020 8:28 pm
by Fisher
Hello.
I tried to fix a snes dead epoxy pcb that was on a case with the Aladdin's label.

I used 2 4mbit flash ROMs stacked over a 2mbit one.
To decode the addresses I used half of a 74HC139, plugged A19 on A, A20 on B, the /E pin on /CART, Y0 to the 1st 4mbit ROM /OE, Y1 to the 2nd 4 mbit ROM /OE and Y2 to the /OE pin of the 2 mbit ROM.

The /RD pin is plugged into the ROMs /CE.
All the other pins are plugged together to their respective data/adress bus pins, but I just get a black screen.

I've tested it exaustivelly but couldn't find the error.
Could it be the address decoding that I'm doing wrong? If so, how can I fix it?

An interesting thing is that if I put the board on a gamegenie I also get a black screen, shouldn't the gamegenie code screen appear?

Thanks in advance.

Re: Help with Aladdin repro

Posted: Mon Jul 06, 2020 10:53 pm
by lidnariq
There's nothing obviously wrong with what you've done. You could try programming my memory map displayer onto the first ROM.

Re: Help with Aladdin repro

Posted: Tue Jul 07, 2020 4:41 am
by poorstudenthobbyist
If you're getting a black screen, even with the Game Genie, maybe there's a bus conflict somewhere? Is it wired correctly, and are the old ROM chips disabled?

Re: Help with Aladdin repro

Posted: Wed Jul 08, 2020 3:10 am
by Fisher
Thanks for the software @linariq.
I'll try to put it there to test.
Would be possible to hack a game genie rom to add this kind of functionality?
It would be a great way to debug the thrash I try to transform into cartridges. :lol:

Yes, @poorstudenthobbist, initially I was suspecting it could be a short circuit somewhere, but I couldn't find it.
Maybe it's related to the 74'139, since it was got from a junk pile and I couldn't test it because it's an smd part.

Could decoupling be an issue?
The stacked memories are plcc32 and the demux is on top of them.
I tried to put 2x 10uf electrolytic capacitors on the pcb, but I didn't see any improvement.

Re: Help with Aladdin repro

Posted: Wed Jul 08, 2020 7:02 pm
by Fisher
As a test, I unplugged the /cart pin from the demux and had plugged it on the /oe of the first 4mbit rom.
I also plugged the demux /e pin to vcc.
I've got a black screen again.
On a emulator I've got a screen with garbled characters and them a black screen if I load the 1st 4mbit only.
I also tried a led plugged on vcc and /cart.
It blinked so fast it seemed to have half bright for about a second them became full bright.
I'll do some more tests with what I have here, but I think this discards a bad demux and points to something else, does it?

Re: Help with Aladdin repro

Posted: Wed Jul 08, 2020 7:16 pm
by lidnariq
Aladdin is LoROM. When you said A18 and A19, I assume you meant SNESA19 and A20, because SNESA15 isn't connected to anything?

Not that I think that's sufficient to explain what's going on here.

Re: Help with Aladdin repro

Posted: Thu Jul 09, 2020 4:03 am
by Fisher
Yes, I skipped SNES A15.
The LED on the Y0 output stood with full bright.
I think I'll try to change the demux and see what will happen.
I need to take a nice picture and post here, but I just can't do it on my crappy phone. :-(

Re: Help with Aladdin repro

Posted: Sun Jul 12, 2020 3:40 pm
by Fisher
Hey Lidnariq, is it possible to hotswap your program?
If so it would be possible to write it to a test cart, hotswap with the repro and them take a good look on what is being read from the ROM.

I already exchanged the demux twice with the same results.
The most thing I could do is to make the bottom half of the screen flash in red, wich is very weird!

Re: Help with Aladdin repro

Posted: Sun Jul 12, 2020 3:47 pm
by lidnariq
Fisher wrote:
Sun Jul 12, 2020 3:40 pm
Hey Lidnariq, is it possible to hotswap your program?
If your SNES doesn't have a functioning CIC, yes. It copies itself into SNES RAM and runs from there.

Re: Help with Aladdin repro

Posted: Tue Jul 14, 2020 2:43 pm
by Fisher
That's a simple and nice tool!
Thanks for sharing.

I tried hotswapping it with some known good games and they have shown the data.
Unfortunately, when I plug the Aladdin cart the console crashes.
I even tried to bypass and disable the demux and got the same results.

I think it probably means I have some wiring issues...
Any tips on where/what I should start looking?

Re: Help with Aladdin repro

Posted: Tue Jul 14, 2020 2:59 pm
by lidnariq
For now, what happens if you disable the 74'139 altogether, so that the ROMs are theoretically all disabled?

Re: Help with Aladdin repro

Posted: Tue Jul 14, 2020 3:16 pm
by Fisher
I removed the wire to the /E pin and left it floating, them I soldered the IC's /E pin to vcc.
The memories should be all disabled with this, but I got the same results.
Is just me who's finding it very weird?

Re: Help with Aladdin repro

Posted: Tue Jul 14, 2020 3:17 pm
by lidnariq
What's the resistance from +5V to ground?

... actually, given the SNES cartridge pinout ... no chance you have +5V and ground backwards, right?

Re: Help with Aladdin repro

Posted: Tue Jul 14, 2020 3:42 pm
by Fisher
It was weird.
Measuring even with the correct or the inverted polarity I started reading 500K and then it started growing.
After I removed the capacitors of the board, I've read 4,8M with the correct polarity and 1,06M with it inverted.
lidnariq wrote:
Tue Jul 14, 2020 3:17 pm
no chance you have +5V and ground backwards, right?
That was one of the first things I checked.
It was corrected, but I may be misreading the pinouts.

Re: Help with Aladdin repro

Posted: Tue Jul 14, 2020 4:09 pm
by lidnariq
Is the original chip-on-board still there? Is there any chance it's interfering with things?

Are any of the address, data, or control lines low-ish resistance to ground or +5v?