Backup RAM & Video RAM errors

OK,

Been doing a few repairs for folks and thought I'd document a couple of things...

Board is a NEO-MVH MV4 (4 slot)

The Read code is broken up into 2 parts... AA and 2A

The first 2 characters are the upper bits and are handled by the IC at D9
The second 2 characters are the lower bits and are handled by the IC at F9


Same thing here... the Read code is broken up into 2 parts... 54 and 55

The first 2 characters are handled by the IC at L9
The second 2 characters are handled by the IC at K9

Enjoy!

RJ

Thanks for sharing

Work RAM, Backup RAM, and Video RAM diagnosing

Work RAM is laid out backwards from Backup RAM and Video RAM on the NEO-MVH MV4


Yeah, I was too lazy to write down the exact address of the error...

The first 2 characters are the upper bits and are handled by the IC at H9
The second 2 characters are the lower bits and are handled by the IC at G9

Enjoy!

OK...

Here's the info on the 6 slot board:

Upper Backup RAM: E9
Lower Backup RAM: F9

Upper Video RAM: L9
Lower Video RAM: K9

Upper Work RAM: J9
Lower Work RAM: H9

Just keep in mind that if you have an error at the bottom boundary then you need to check traces.

For example a video error of:

Shows up on the zero boundary. You need to check to see if the traces (wiring that is on the circuit board) are all good. A bad trace or a bad chip can each cause this type of error.

Another item to note...

If you have an error such as this:


Then you have a different problem all together.

This is caused by the chip not being selected properly for read/write access. This is almost always (well, I'd say > 99.5%) a problem with the chip or with the trace that is controlling the SRAM and NOT with the SRAM.

Look for broken traces whether from battery leakage or someone scraping something across the board which physically damaged the traces. If that's not it then trace back the chip control traces to see what chip is feeding it.

On the 32k x 8 SRAM ICs (the 62256 or equivalent) that are used for the Backup, Work, and Video RAM that would be:


OK, OK... the * in front means it is an active low signal. If it's high, it's not being signaled. If you get NO signal from your logic probe on one of the pins then you have an open trace for sure.

Pin 20: should always be grounded on the Work RAM and Video RAM. That pin is directly connected to ground and if it isn't then you have a physically damaged trace. On the Backup RAM it is used to put the chips into low power standby mode.

Pin 22 & 27 connect to different chips. These are the ones you are most concerned with when troubleshooting this type of problem.

Oh, when troubleshooting these you WILL have to strip off the red cardboard and the black foam under the circuit board in order to follow the traces. Have fun cleaning all that crap off. Yuck.

Hope this helps you keep your MVS alive!

RJ

I also have a Video RAM Error:
Address: 00000603
Write: 5555 Read: 5575

If I am understanding all of the posts that I've seached, I must have a bad ram surface mount chip in K9 on the board (Or bad traces/connections to that chip)? Any help would be gladly appreciated!

EDIT: BTW it's a NEO-MVH MV4 (4 slot)

It's definately a bad chip since it's not an error message at a zero boundary (00000603 vs. 00000000)

It's a surface mount chip. I have 'em on my website.

RJ

If the error changes with every power up, then it is in the select lines with garbage. If it stays the same, it is a bad bit within the RAM chip itself.

Nightmare Tony said:

If the error changes with every power up, then it is in the select lines with garbage. If it stays the same, it is a bad bit within the RAM chip itself.

Click to expand...

Holy shit, look who come home. So you took my advice and decided to come back to the forums I see. Thanks for the email help btw

No prob, always glad to help. Just been insanely busy these days, had been working on my nhaunted house (thje black plywood habitrails), new job designing security systems and doing a movie soundtrack. Had finished building a theremin for it and the next project is rebuilding a pump organ fdor it as well.

In other words, insanely busy as always.

Keep me up in here. SNK is in the tie for my top 3 favorite jobs which are SNK, Romstar and my present job. Special 4th place for a job that jmoved that I always loved.

sram surface mount soldering

I don't have the tiny tools meant for this tiny soldering but I recall a tutorial page that showed a dude soldering on extra ram to his xbox 1 motherboard. He soldered two corner pins and made sure it was on straight and then gobbed a bunch of solder over all the pins. Then he used a desoldering braid to get the excess. Is this method worth attempting? What's is the real method for soldering on this small scale?

(I ordered some sram to fix my "Video RAM error" in my 4slot)

There is a way to do it without having the surface mount gear but it's a little risky.

Take a very sharp disposable razor knife - the kind with the break off blades - and put just barely enough tip out to cut and cut the pins off at the chip body.

It takes a sharp knife so you don't rip the pins and pads off the board. You want just a tiny tiny amount if blade sticking out and rest the body of the knife on the body of the chip to help prevent the blade from cutting traces on the board under the chip.

Once the body of the chip is cut away, take a bit of liquid resin flux (not acid flux!!!!!!) and put it on the pins/pads. Then you can take the soldering iron and 'wipe' the pins right off the board. It takes very little pressure to do this as you don't want to pull the pads off the board.

Next is cleaning up the pads. Use a vaccum desoldering pump or solder braid. Just be careful to not use too much heat as again, that could lift the pad off the board.

Now that the solder pads are clean lay the chip down. Be SURE it is oriented correctly! You don't want to solder down the new chip just to notice it's in backwards! Be sure to have the legs of the chip centered on the pads then tack the 4 corners down with solder.

Take the liquid flux and put some down the pins on both sides of the chip. This will help the solder flow and stick to the legs and pads better. Put a small ball of solder on the tip of the iron and hold the board up at about a 60 degree angle, put the soldering iron on the pins at the highter end slowly pull the iron down towards the lower end, soldering all the pins down the side at once.

If there are pins bridged then wipe the soldering iron tip clean, add a little flux to the bridged pins, and wipe the soldering iron across them to remove the extra solder. It takes practice but it's easy to learn to solder them down with the hot iron method.

RJ

Video RAM Error

Video RAM Error:

Address Write Read
00008000 5555 FF55

I got this error and installed a RAM chip at L9. After hooking up this MVS 4 Slot again and power it on I get the same error!? I thought at least I would get a different error. I saw in another thread to try shorting pins 13 and 14 to narrow down the bad chip. When I shorted the newly installed L9 I get

Video RAM Error:

Address Write Read
00000000 5555 FF51 (or was it 5155?)

When
I short K9 I get some garbled text with lots of AA's and 11's

Hepl?

There are two different pairs of video RAMs and therefore two different errors: when the vram error address ends in 8000 it's the chips located at L11 and M11 (on a 4-slot, older model), i.e. a couple of Sony CXK5814. When it ends in 0000 it's the surface mount chips located at K9 and L9. You simply pulled out a good RAM instead of the bad one (which may not necessarily be bad, you need to check its connections first). The above difference should always be stressed when starting a thread like this or else what was meant to be helpful turns out to be harmful...

MKL said:

The above difference should always be stressed when starting a thread like this or else what was meant to be helpful turns out to be harmful...

Click to expand...

MKL: You would rather NOT have things like this started? If you have a problem with a thread and feel there is information missing from that thread, how about you be helpful and state it rather than slam it?

NCFlagg, The error at "00008000" is referencing a different set of chips than an error at "00000000" - This thread is for troubleshooting the different surface mount RAMs on the Neo Geo systems and didn't include the DIP style video RAMs. You have a failure in one of the CXK-5814 chips.

I documented these errors and chip locations to try and help the community. If anyone feels there are mistakes or omissions, feel free to add to it. Be helpful rather than bitchy... And if you aren't sure if there is a mistake and want to ask a question, ask it! Ask it in this thread, open a new thread, send me a PM, etc... The only dumb questions are ones that aren't asked.

RJ

It's not implied in any way in my post above that threads like this had better not be made. As for being helpful, I did point out the difference between the two errors/RAMs and put the guy on the right track. Too bad he's got two things to fix now though. Then I just added a warning remark that wasn't aimed at you in particular but at everyone (including myself) who intends to share tech info. It's very easy for someone in the know to involuntarily omit something that is perfectly clear in his own mind. The point is that we often tend to forget that the people that are supposed to benefit from our info are total noobs that cannot judge critically what they read and integrate something that has not been stated.

You should choose better words when you write your posts. It came across ugly.

bad lexical choice > omission of crucial info

I think MKL was only trying to help. Thanks to you both. I was thinking from what I read above that 00000000 was a circuit path problem and everthing else lead to either L9 or K9. No biggy.

So it looks like my upper 5814 needs replaced then correct? I've been looking around trying to find a couple CXK5814P-35L 's to order but the only thing I can find has a minimum order of $100 to $300 order request. Is there an easier place to find them? Can I pull one from an old video card or something?

Whatever...

Mods, can we get the pissing contest split off the thread and moved to the war room?

RAM

Ok, I installed the CXK5814 ram that Channelmaniac graciously sent me. With no games installed I get a blue and white crosshatch! Woohoo! I tried one game in slot 1 (white arrows matching up) and got a black screen. Tried all games in at the same time with same result. Tried again with no games and got a crosshatch again.

Did it start with green screen then went black? Check switch #8, the freeze switch should be off.

I don't know if it ever went green because I'm turning it on from the back. Yes, switch #8 was on. Thanks for the tip. I didn't see the switch settings anywhere in the manual I have.

It works now!!!! Thanks, everyone for all your help. It's much appreciated. I plugged in Real Bout and even got sound.

I can't believe that surface mount ram install actually worked lol. Well, I only ripped off ONE of the pads....

Glad ya got it going. Enjoy!!!

Congrats man!

There's a huge bit of satisfaction in fixing something

RJ