snes Dram issue

mvsfan · Post by **mvsfan** » Sun Feb 08, 2015 1:29 pm

I have a 1-chip snes that comes up on the test cartridge with A Dram Fail.

It also glitches the graphics, but continues to play the game.

how can i figure out wich of the two chips is bad? just replace them both?

also, are the dram chips the same between revisions or did they change them on 1-chips?

I have a couple spare boards with dram thats probably good but they arent 1-chips.

kamiboy · Post by **kamiboy** » Sun Feb 08, 2015 2:07 pm

What is this test cart of which you speak. Does it exist as a rom? Because I need to test a SFC with glitchy graphics.

mvsfan · Post by **mvsfan** » Sun Feb 08, 2015 2:37 pm

it does. its snes burn in test cartridge revision D.

kamiboy · Post by **kamiboy** » Sun Feb 08, 2015 2:51 pm

Cheers, mate.

kamiboy · Post by **kamiboy** » Sun Feb 08, 2015 3:31 pm

Are you using the actual test cart or a flash device with the rom? Because bugger me if I can find a working link of the rom online, they all seem to be dead.

Xan · Post by **Xan** » Sun Feb 08, 2015 3:43 pm

That rom can be found in goodsets.

kamiboy · Post by **kamiboy** » Sun Feb 08, 2015 3:47 pm

Found it, thanks.

CkRtech · Post by **CkRtech** » Sun Feb 08, 2015 9:35 pm

mvsfan wrote:I have a 1-chip snes that comes up on the test cartridge with A Dram Fail.
...
how can i figure out wich of the two chips is bad? just replace them both?

Sometimes issues with graphics that are related to the ram happen because of the path/traces to the chips rather than simply the chips themselves. Do you already have this open? How does your board look?

kamiboy · Post by **kamiboy** » Mon Feb 09, 2015 6:18 am

Looks like trouble. Gotta check those traces, but my board looks clean to the naked eye.

Ed Oscuro · Post by **Ed Oscuro** » Mon Feb 09, 2015 6:52 pm

Wouldn't VRAM be LOW not HIGH if there was trace damage?

Xan · Post by **Xan** » Mon Feb 09, 2015 7:15 pm

The SNES VRAM is split into low and high sections, one chip each, so this probably indicated which of the two chips failed. If you interpreted it as "low VRAM count" that would be pretty pointless, as there already is a "VRAM count" listing below.

kamiboy · Post by **kamiboy** » Mon Feb 09, 2015 7:17 pm

I thought the HIGH marker was to be used to identify which of the two VRAM chips was failing the test. I must admit I am way above my head here.

Edit: looks like my assumption was verified while I was typing, the question is whether the chip in question needs to be replaced or just in need of a reflow.

Ed Oscuro · Post by **Ed Oscuro** » Mon Feb 09, 2015 8:00 pm

Xan wrote:The SNES VRAM is split into low and high sections, one chip each, so this probably indicated which of the two chips failed.

That makes sense - I was thinking it was low/high voltage (I didn't think ROM would have a way to test that directly, so it would have been assumed, as if attempting to write 0 still returned a read of 1 to various bits, or something...it's probably hiding these actual tests under the hood and the results should be interpreted as you say)

Xan · Post by **Xan** » Mon Feb 09, 2015 8:11 pm

kamiboy wrote:I thought the HIGH marker was to be used to identify which of the two VRAM chips was failing the test. I must admit I am way above my head here.

Edit: looks like my assumption was verified while I was typing, the question is whether the chip in question needs to be replaced or just in need of a reflow.

Reflowing would mean taking the path of least resistance, though if that chip is really bad I'd think maybe another component somewhere could be responsible for that. How common is it for RAM chips in systems of that vintage to just go bad? I've heard about it a lot with arcade PCBs, not as much with consoles.

Ed Oscuro · Post by **Ed Oscuro** » Mon Feb 09, 2015 11:28 pm

What's the part# and vendor? We should do some research on this.

mvsfan · Post by **mvsfan** » Tue Feb 10, 2015 12:07 am

also - this snes i have will still play some simple early games like super baseball simulator 1000 Perfectly, if thats an indicator of what might be failing.

I picked all the pins on the Ram chips while it was off to see if any were loose because there was some bug mess in it. But none of them seem loose.

Im also going to clean the board with contact cleaner and see if that helps.

my ram chips are SONY CXK582578M-10LL on the 1-chip. Couldnt find a datasheet on these, or much info at all.

the ones in the snes i want to use to replace the chips are

MOSEL MS62256CL-10FC chips. I found the datasheet right away.

mvsfan · Post by **mvsfan** » Wed Feb 11, 2015 10:49 pm

Um, is there still any interest in this? I updated my previous post with new info. ^

CkRtech · Post by **CkRtech** » Thu Feb 12, 2015 12:06 am

<Rubbing my forehead with my hand>

I am sorry, mvsfan. You mentioned graphics glitches and a "DRAM" fail. The two chips are used for VRAM (and are the ones that would typically cause graphics glitches). I don't believe your diag cart is saying you have VRAM issues, right? I didn't catch this until now because the image posted to the thread after I wrote my earlier post was from kamiboy - who *is* having issues with VRAM (be it the chips themselves or - most likely and hopefully - the path/traces to those chips).

As cheesy and simple as this question sounds, have you cleaned your cartridge slot really well and made sure the pins are still making good contact with your carts?

mvsfan · Post by **mvsfan** » Thu Feb 12, 2015 1:21 am

yeah, it says Dram error, not VRAM. sure, ive cleaned the cartridge slot good. i always try that first.

so your saying that the two chips im referring to are not DRAM? where would it be located?

Btw, i have some older schematics for snes but its SHVC.

does one even exist for the other revisions?

trap15 · Post by **trap15** » Thu Feb 12, 2015 1:50 am

Those chips are indeed VRAM. The DRAM is a custom part, it should have "S-WRAM" or so written on it. There's a pinout here: http://problemkaputt.de/fullsnes.htm#sn ... tsramchips

mvsfan · Post by **mvsfan** » Thu Feb 12, 2015 2:27 am

now it makes a lot more sence. I didnt bother checking that chip for continuity because I thought that was well, Wram.

I had checked the two vram chips and the pins all rang out fine.

trap15 · Post by **trap15** » Thu Feb 12, 2015 2:34 am

It's both

I'm not sure why the tester has DRAM and WRAM and doesn't have it fail both if it fails one... The WRAM is a DRAM part, and as far as I can tell is the only DRAM on the system.

kamiboy · Post by **kamiboy** » Thu Feb 12, 2015 8:28 am

Ed Oscuro wrote:What's the part# and vendor? We should do some research on this.

LH52A256NF-IOTLL
LSI LOGIC

kamiboy · Post by **kamiboy** » Thu Feb 19, 2015 5:27 pm

Well, just as expected reflow didn't help. Looks like I am going to have to replace one of those two ram chips.

mvsfan · Post by **mvsfan** » Thu Feb 19, 2015 5:47 pm

By the way, just so people know if your using Sd2snes, The Hv Timer test will always fail.

if it passes all the other tests theres nothing wrong with the snes.

shmups.system11.org

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