Problem with Akumajo Densetsu eproms on real cart

Hello!

I have decided to put the English translation of Akumajo Densetsu on my real cart and I followed the tutorial here .

I had no problems removing the old mask roms and soldering the new eproms.
I have triple-verified the 2 eproms: AMD 27C010 -120DC and TMS JL 27C020-15

The problem I have is that after an initial ~30mins gameplay the screen just went black. Reseting did not help , I had to remove the cartridge and insert it after a while. Then it booted again for ~10 seconds then it went to black screen again... the longer you leave it outside the longer you might use it , a classic symptom I guess.
Nothing burned and the famicom works fine. And the cart works for a while provided you leave it alone...
I have no idea why this happens, could it be that my eproms are crap? Already made a Gargoyle's Quest II translation cart with the 27C010 eproms, it runs perfect (used this tutorial here )

Here are some pics of my work on the cart, there are no burned traces or anything suspicious



mask roms removed:


eprom work:






and the back with the eproms soldered:


and here it is working for the little time it does:


Any ideas of what to check? Any help is welcome, thanks in advance!

Are any of the pins left floating? (not connected to anything)
That can cause problems. If they're floating, tie them to +5V or GND based on what your EPROM spec sheet tells you. (Usually PGM is tied to +5V).

There is one floating pin on the 27C010 , pin1 that according to the datasheet is "VPP = Program Voltage Input" , everything else is connected...

The guide also tells to connect pins 30+31+32 together as to get Vcc to pin32 (there are no holes on the pcb for pins 1,2 and 31,32)
So pin 30 that is N/C to the datasheet actually gets power and via connection pin32 gets power too. But pin31 is "Program Enable Input" and gets the same 5v... could that be the problem on the specific eprom I am using and after some time the eprom goes to write mode or something?

You should tie all pins that "don't care" (like pin 1) to +5V or GND, but don't leave them floating.
See if that fixes your lockups.

I'll try it, what's the suggestion for pin1? GND?
TIA!

Some EPROMs (namely Texas inst) *REQUIRE* pin 1 (Vpp) to be tied to Vcc for reading. I'd just tie it to Vcc reguardless, but the real answer is hidden in the truth table of the datasheet of your EPROMs.

One other thing I've seen that I'm not quite sure actually happened or not to me recently is early on 'bit rot' of EPROMs. Not sure if it had something to do with them being freshly erased or what. But I'm pretty sure I've properly programmed EPROMs before including the verify step, but then ~30 mins later I try to verify it was programmed properly and there is a bad bit in the EPROM. Obviously I can't be sure as to what your problem is but if you've exhausted all ideas and don't have a means to dump the cart you can remove the PRG EPROM and try again. Don't bother with the CHR ROM, it can't really cause a problem like this, it'd only show up as visual 'glitches' if there was a CHR issue.

Well I have checked the soldered TMS27C020 eprom: Vpp + PGM + Vcc are all connected to the +5v line
I have found the datasheet and the way they are connected atm seems fine to me:



I am all out of ideas atm regarding the 27C020 part...

I will try now and remove pin30 of 27C010 and get it out of the equation (maybe it does not like +5v) and connect the floating Vpp pin to VCC, since it's datasheet recommends it (though floating pin1 works just fine on the Gargoyle's Quest eproms... and I've been playing it lots... maybe the KONAMI board is different in that aspect)

edit: cross-checked pinouts of the original mask rom and the 27C020 , they match.
I also made some work on the 27C010: removed pin 30 that is N/C , and soldered Vcc in all 3 pins: Vcc + PGM + Vpp as per datasheet... it did not improve though...
It could be the case that the TI 27C020 is not playing well?

edit2: I have replaced the 27C020 with another one (same model/specs) and this time it seems to work fine... I am now at 1.5hrs and the game still runs.
I also tested the old eprom on the programmer, it's data is OK. Maybe it's not a good part in regards or access speed , or it just develops errors after some time of usage.

Eproms get slightly slower after a erasure/programming cycle. That's how EPROMS die out.

If you're buying them on EBAY from Chinese dealers there's a good chance you're being sold EPROMS that not only are very old but also have gone through several reprogram cycles. Sometimes they get so slow they're not usable for something like the NES/Famicom even.

Keep that in mind when working such projects.

yeah l_oliveira , that's what I found out too... I got them from eBay/china, they were advertised as "new" ... here is the eBay BIN sale ...
I am happy at least one works fine, as I only needed one thanks to my "ocd" I always get double of what I need, this time it payed out

Also, I forgot to mention, a good way to achieve more speed from a EPROM is tie down it's /CE pin (chip enable) to GND and use /OE (Output enable) instead to enable reads from it. That way you save the time the chip wastes while going back from/to low power mode.

That would probably fix your issue with that particular EPROM chip.

by "use /OE (Output enable) instead" I gather you mean give it Vcc, right?

No, you take the pin 22 to GND and connect pin 24 to the trace that go to pin 22 to it. Well you could use the multitester to check if the cartridge isn't already desgined like that. Because the 32 pin ROM has /CE and /OE. The 28 pin ROM has only one enable pin.

ah, thanks for that, I got it

ps.
I'm gonna add my OT question at this post, because the earlier one got buried since you answered at the same time as my edit
Is there a reason why everyone is using UV erasable eproms? Aren't Electrically erasable eproms better? or they aren't compatible? I have read on the internets that electrical ones last longer that the uv ones, isn't it a better thing?

I do prefer FLASH myself but they're more expensive... Probably because they're easier to deal with.

so I could have just used flash roms for my 2 projects... I'll keep that in mind for the next ones, thanks!

I am horribly late, but here's my only guess:

You have a bug that appears 30 minutes in, but then triggers almost immediately. The only behavior that acts like that (AFAIK) is overheating.

keropi, EEPROMs are quite expensive. Flash and EPROM are way cheaper.

@lidnariq:

I thought so but all chips were cool on touch... I ended up replacing the 27C020 and the problem went away...

@socram8888:

for my next project I might chose something else than UV eproms, I don't mind paying more if there is better performance/reliability involved (assuming there is a difference ofcourse...)

It's personal preferences. Also with UV EPROMs device looks more vintage