SNES multicart worth fixing?

[Fisher]

I've found another one, slightly different, sory for the crap pictures:

SNES Multicart 2.png (10.03 KiB) Viewed 1138 times

Looks a lot like some NES' discrete mapper.

Unfortunately, testing with Lidnariq's program that shows the ROM contents on-screen only gives me 0.
Looks like the blob is dead too and it's even passing the diode test.
Any suggestions other than building a new game with an EPROM or discarding it?
Thanks in advance.

[lidnariq]

No, no suggestions. Without any idea what's wrong with the ROM, I can't suggest what to try instead.

[Fisher]

Well, I have absolutelly no idea too.
And I guess that even if I had better tools to test it there shouldn't be much of a difference.

I tested the ICs of the mapper and they are fine.
I still get all 00's when trying to "view" the ROM, wich probably is telling that it isn't being enabled at all.
Checking /RD and /CART from the bubble with the multimeter gives similar results as the other "pins" of it.
Maybe I should try to pull these pins down, or even plugging it to GND disconnecting from the console, wich probably would force a conflict...

I tried to heat the bubble from another board, 150º for 30 seconds, and the only difference I could verify is that the diode test gives me a higher number, or should I say resistence?
I've read some people say that sometimes heating it with an lighter makes it boot again, but I think too much heat would make the bubble fall from the board, because that's the way I use to remove them.
I also think that the heat and time I used is just a fraction of what I should get from a lighter. Maybe I should try more heat for more time?

So... I think I already know the answer to this, but I'll keep trying for a while since I've got around 40 of these boards so anything I could fix is good and I think I should try to revive them before using the board simply as a base for another repro.

I 'm also a little surprised, since I tought pirates of the SNES era were just limited to copy the games, but I'm seeing multigames that have had a nice selection menu, wich was very common on NES pirates but I didn't know about it on the SNES.
There's also others that are a little different, some using PAL chips and even one that seems to be a multigame with a DSP-1 clone onboard.
I intend to share the info I get from them, as soon as I get some...
Maybe this can be useful to someone, who knows?

I also ask that please take a look on the schematics and see if they make sense.
Altough I review my notes and hand draws a few times before coming to the PC, sometimes mistakes are not fixed on the process.
It's a nice way to spend a little time alone, learning some nice things while the lockdown lasts.

[lidnariq]

I tested the ICs of the mapper and they are fine.
I still get all 00's when trying to "view" the ROM, wich probably is telling that it isn't being enabled at all.

Check at other addresses. That program uses "absolute long indexed with X" to read things, so the open bus value is set to the bank. If it changes from $00 to follow the top byte of the address, then you can be unfortunately confident that the ROM is just not enabled. (start & select: ±$100000. shoulder buttons: ±$10000. dpad horiz: ±$1000. dpad vert: ±$100. A/Y: ±$10. B/X: ±1)

I tried to heat the bubble from another board, 150º for 30 seconds, and the only difference I could verify is that the diode test gives me a higher number, or should I say resistence?

The forward voltage of all diodes is a function of temperature, going up 86µV per °C.

I also ask that please take a look on the schematics and see if they make sense

Yeah, it's very similar to the one from this megadrive cart (although pictures are missing) - because both the SNES and Megadrive boot from the bottom of the available range and usually don't care about mirrors, the OR gate can just move the starting address up to point at the next game.

It's a nice way to spend a little time alone, learning some nice things while the lockdown lasts.

siiiiiiiiiiiiiiiiiiiiiiiiiiiiiigh.

[Fisher]

I did a small discovery that I would like to share.
Sometimes, in single games with multiple "bubbles", the demux is incorporated on the CIC clone.
If for some reason this IC doesn't work and the "ROMs" are fine, it's possible to add an external demux by cutting the tracks that go to the bubbles' /CE (or is it /OE?) pin.
In some cases there's even a space ready to accept an 74'139 or a 74'00, most of the time the IC expected is written on the PCB.
Hope this little information can help someone else.