Pokémon Crystal bad SRAM chip?

Hi,
I bought a lot of Game Boy games on eBay, and ended up with an extra copy of Pokémon Crystal. However, this extra copy had its SRAM battery repaired by a monkey. By which I mean the battery tabs had been pried off the original battery, and then soldered directly to the sides of a watch battery.

Backwards. The polarity wasn't even right.

And that's where I assume the problem lies. I removed the monkey battery and soldered in a solder tab CR2025 like you're supposed to, plugged the cart into my GBA, started and saved a game, did a software reset (Select+Start+A+B), and the save was already gone. I didn't even need to turn the Game Boy off for there to be no save file.

Has anyone experienced an issue like this before? Is this cart repairable, or even worth repair in the first place? I'm not the best at SMD soldering — it feels like I'm soldering with a baseball bat — but if this cart is otherwise worthless I'd be willing to swap the SRAM chip if a new one is easy to procure and isn't expensive. But is that even what's wrong?

I'm not sure how to troubleshoot this further, as when I did a battery replacement exactly the same way to a copy of Pokémon Silver and the boards looked nearly identical it worked just fine…

 

If the game runs OK, the RAM is probably fine - there is also a memory protect IC that has the job is disabling writes to the SRAM when the cartridge is not powered up (MM1134?) - it's quite possible that that didn't like having a negative Vbat applied to it. If it is a MM1134, then it should have the battery voltage on pin 4 and a slightly lower voltage (~2.9V) on pin 6 even when the cartridge is not powered up. You can also check the power pin on the SRAM when the cartridge is not plugged in to see if it has power (I think it's a 128KB / 1Mb SRAM in that cart, so the power should be on pin 32).

 

I'll have to check voltages when I get home as my meter's not with me. It does have a chip that the board labels MM1134 with the part number 67351501 printed on it. I'm guessing that's the IC you're referring to? Especially since my Silver Version's PCB has an identical-looking chip with 031134A silkscreened on it.

I'm pretty new to the anatomy of Game Boy cartridges, but for reference here is a couple photos of the bad Crystal PCB and a good (repaired) Silver PCB: http://imgur.com/lAua9YN,ULdtsRs,WEZm0oG

I imagine the corrosion on the Crystal board probably doesn't help, but it didn't look to me like it was shorting anything. However I'm wondering if maybe I should desolder the battery again and completely clean the board before putting it back.

 

Yeah, that's the SRAM supervisor chip - you can see that the battery +ve is wired through a 200R resistor to pin 4. It looks like I got the size of the RAM wrong - that's a 256kb / 32kB device, so the power will be on pin 28 - you should be able to measure the battery voltage minus one diode drop across C5, even when there is no power on the cart. If you find you have voltage on pin 4, but not across C5, then the Mitsumi chip is almost certainly bad.

If you mean the flux around the battery pins, it shouldn't cause any problems, although cleaning it would make the board look nicer.

 

The picture must have not done the board justice — it seemed to have water residue and such on both sides, not just a horribly botched soldering job. But nevertheless, cleaning it to remove the corrosion, using a desoldering wick to reprep the solder pads for the battery (in case the giant blobs of solder were shorting something nearby), and alcohol'ing the flux away before ultimately resoldering the battery to the board did not make any difference after all.

I'll check the voltage across pin 4 and C5 and see if C5 has voltage. If not, where can I get another Mitsumi MM1134? Are they possible to buy, or would I actually have to buy a donor cart of some sort?

 

It's an obsolete part, but still available in the secondary market - you might have to order it from China, since that seems to be were most of the old chips end up.

 

I do have a voltage across C5.

Battery reads 3.2V across (it's a brand new CR2025 rated for 3V), negative vbat to pin 4 on MM1134 reads 1.28-1.29V, and C5 reads 1.05V across with the positive lead closer to the battery.

 

OK, that sounds a lot lower than I would have expected - it's likely that the MM1134 is faulty. If you have another cartridge with one of them on it, then try swapping it to verify.

 

Okay, gotta bump this thread now. I got a copy of Pokemon Red on eBay that was advertised as "NO BOOT," and the seller wasn't kidding: the original battery had clearly been forcefully ripped out, and then a solder tab replacement was taped in, for fuck's sake. I paid $5 for it hoping I might be able to fix it (and not really caring if I couldn't), but I didn't expect it to be this bad… the Nintendo logo would appear correctly/not corrupted, but then it would freeze and something would start smelling like ozone… Nevertheless, I might have an extra working MM1134 now. I mean, I wouldn't be surprised if this one is bad too given the state of the cart it came from, but we'll see.

I soldered it in (I need to buy a 3rd hand and some tweezers, this was even harder than I expected!) and I only had a DMG on hand to test it with so I could only confirm it turned on. I'll update this when I get home and can try on a more compatible Game Boy.