nesdev.com
http://forums.nesdev.com/

Bad eproms that verify?
http://forums.nesdev.com/viewtopic.php?f=28&t=13719
Page 2 of 2

Author:  icemanxp300 [ Fri Jan 20, 2017 8:31 pm ]
Post subject:  Re: Bad eproms that verify?

Ok what is going on here people. Look at the date I made this thread. It was exactly 1 year ago. I purchased a batch of chips in December and January they gave me problems.

Now the same exact thing happened. I purchased a batch of chips last month "December" and they program bad again just like the batch did a year ago.

However here is the kicker, Only on snes. I was trying to diagnose the problem and since I make genesis games as well now, I tried a genesis game and it worked. So Then I went back and tried snes again, multiple games and same thing, bad glitches on all.

So I grabbed the batch of chips I got over a year ago that would not program correctly and tried a genesis rom on them and it worked!!! Unreal. What is going on here. I'm glad I can use the chips now but what is going on here.

They are all 100F1

Author:  Ice Man [ Sat Jan 21, 2017 3:40 pm ]
Post subject:  Re: Bad eproms that verify?

Sounds like your SNES board is defective or your soldering is wrong. If ICs usually erase, blank check or verify they're 99% fine. I never had problems with EPROMs unless they didn't blank check or erase, those have been thrown in the trash.

How did you solder the 27c160 to a SNES board? Which SNES board did you use as a donor?
SHVC-1AXM
SHVC-1AXB
SHVC-1JXM
SHVC-1JXB
etc..


Genesis is simple so there's barely any error potential at all.

Author:  thefox [ Sat Jan 21, 2017 4:35 pm ]
Post subject:  Re: Bad eproms that verify?

Maybe they are too slow for SNES. (Disclaimer: I have no idea how fast the Mega Drive ROMs have to be.)

Author:  tepples [ Sat Jan 21, 2017 7:55 pm ]
Post subject:  Re: Bad eproms that verify?

The 65816 requires memory to return a value within a half cycle, which is 200 ns (slow ROM) or 120 ns (fast ROM). But the 68000 accesses memory only once every four CPU cycles. Because of this, a Genesis cartridge can use much slower memory if it isn't going to be DMAing from ROM.

Author:  icemanxp300 [ Sun Jan 22, 2017 12:40 pm ]
Post subject:  Re: Bad eproms that verify?

Ok, what makes zero sense is I can order some m27c160 chips today and get them in and they can be identical and work fine.

Like I have programmed snes games all last year using these chips and the same adapter boards and same games. Here is a picture, the 2 chips on the left programmed fine, the two chips on the right will not.

If you look at the two chips in the middle they are 100% identical as far as the "I assume batch numbers" one programs fine, they other will not. It is only for snes though. All 4 of those chips will program perfectly genesis games but only the 2 on the left program correctly for snes.

So going over this speed thing, could it possible that some of these chips for some reason have some how "slowed down" and as such they are not fast enough to program snes properly now?

It is not a soldering problem or a wiring problem. I don't even solder until they go through my tester board which I have used to test 100's of snes games with. This problem is chip specific that is 100% guaranteed. As far as the boards I use, I use them all it doesn't matter as long as the donor has 36 holes instead of 32. so boards like 1aon-20 or 1a3m-11 anything if they are lo rom. Any hi rom works as well as long as they have 36 holes which I don't think I have come across a 32 dip hi rom donor yet.

So I am leaning to 1 of 3 problems.

1. The speed of the chips like thefox and tepples mentioned has slowed down.
2. The programmer/software is buggy
3. The adapter board is buggy

The only one that makes sense is 1. As I can and do program many of these chips perfectly fine.

Is there a way I can test the speed of these chips to see if some of them are not as fast as they should be?

Attachment:
100_8069.JPG
100_8069.JPG [ 2.96 MiB | Viewed 434 times ]


...

Page 2 of 2 All times are UTC - 7 hours
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/