Trying to read EPROMs, M27512

pxl3d

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Hi,
Sorry about the noob question.
I have a Double Dragon bootleg that has graphical glitches (some vertical lines in certain sprites/tiles, sometimes on/off).
I would like to at least confirm that the EPROM's checksum concur, but I can't seem to be able to read part of the EPROMs.
This is the board : https://edgeemu.net/details-8248.htm

I can read the 27C256 on the board, but not the 27512, at all, I get FF's everywhere. If I read them as 27C256 I get data, and corresponds to the second half of the bank of the ROMs from the mame archive.

I have a Xeltek Superpro 500P, that is very versatile but not with this.

Thanks anyone in advance. :)
 
Have tried to read them based on the eprom brand and size as it appears on the label, as opposed to the generic 27512 type? E.g. MBM27512 etc.
 
Have tried to read them based on the eprom brand and size as it appears on the label, as opposed to the generic 27512 type? E.g. MBM27512 etc.

Yeah they are OKI M27512ZB, and one TMM24512... All don't seem to read.
 
It may be easier to burn a set on known good 27512s and move on with your troubleshooting, you can always come back to this. I like the EEPROM type if your programmer can handle those, instant erasing, no need to UV erase them.
 
If you can get half the data when reading as a 256, but get all FF's when reading as a 512, that sounds like an issue with the programmer to me, given you're having the same issues with multiple 512's...

Settings are important when writing the EPROM - when reading, it really shouldn't make a difference typically. The game board doesn't know what brand/model of 512Kb EPROM you're using after all..
 
If you can get half the data when reading as a 256, but get all FF's when reading as a 512, that sounds like an issue with the programmer to me, given you're having the same issues with multiple 512's...

Settings are important when writing the EPROM - when reading, it really shouldn't make a difference typically. The game board doesn't know what brand/model of 512Kb EPROM you're using after all..

I've had tremendous compatibility up until now with this programmer. :(
Do you think there's a way to force the programmer to switch banks ?
 
Oh, I don't think it's a compatibility issue; I'd expect that programmer to handle those fine. Do you have any other higher capacity chips (ie, 1Mb, 2Mb, 4Mb, etc.), and does it read those without issue? If you can read a 27010, 27020, etc, without issue, then this would be odd indeed.

As for forcing bank switching - you could make up a small adapter that would allow you to configure your programmer for a 256, and then manually toggle the highest address line to force the bank to switch (if memory serves) as a way to toggle between the upper and lower 256 bank... a bit of a pain, and you may want to simply take a new 512, see if it burns and can be read successfully afterwards before going through that hassle...
 
I've burned 010's, 020, 040, 080, 256 and 27C512 without a hitch many times over, but I can't read anything off of these 27512 I have on this bootleg Double Dragon to make sure if EPROMs are a problem, or the SRAM.

Oh, I don't think it's a compatibility issue; I'd expect that programmer to handle those fine. Do you have any other higher capacity chips (ie, 1Mb, 2Mb, 4Mb, etc.), and does it read those without issue? If you can read a 27010, 27020, etc, without issue, then this would be odd indeed.

As for forcing bank switching - you could make up a small adapter that would allow you to configure your programmer for a 256, and then manually toggle the highest address line to force the bank to switch (if memory serves) as a way to toggle between the upper and lower 256 bank... a bit of a pain, and you may want to simply take a new 512, see if it burns and can be read successfully afterwards before going through that hassle...
 
I've burned 010's, 020, 040, 080, 256 and 27C512 without a hitch many times over, but I can't read anything off of these 27512 I have on this bootleg Double Dragon to make sure if EPROMs are a problem, or the SRAM.

I'd suggest to burn a set on known good 27512s and move on with your troubleshooting, you can always come back to this. Have you checked the logic state on the pins on the SRAM ICs, or try to piggyback them?

paris
 
OK there is a store that carries 27512's locally, I'll stop by to grab a few.
Checking logic states would be the next step in my learning to troubleshoot boards ! :) I have the probe and a scope... Need to learn how to use them.

Edit: Thanks very much for your input, very generous of you (and everyone else!)

I'd suggest to burn a set on known good 27512s and move on with your troubleshooting, you can always come back to this. Have you checked the logic state on the pins on the SRAM ICs, or try to piggyback them?

paris
 
but I suppose the schematics must be similar.

I believe so...

You know, at some point the cost of buying a working PCB vs. time/effort/parts for the repair may be similar. I am not saying you should not repair it (especially being a bootleg with less street value vs. an original, UNLESS it does not suffer from slowdown issues of the original), but I would consider it as a learning experience... only you can make that call! However, repairs are very rewarding even on PCBs with limited monetary value.
 
I do believe this bootleg suffers from slightly less slowdown than the original board ! And this game is one of my favourite from my childhood, so I'd like to have it up and running spic'n'span. :)

I'll check the SRAM pins with the scope and try to read / write 27512 eproms from the store and post some pics later this week.

I believe so...

You know, at some point the cost of buying a working PCB vs. time/effort/parts for the repair may be similar. I am not saying you should not repair it (especially being a bootleg with less street value vs. an original, UNLESS it does not suffer from slowdown issues of the original), but I would consider it as a learning experience... only you can make that call! However, repairs are very rewarding even on PCBs with limited monetary value.
 
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