6-slot (MV6) repair in progress

[lithy]

I picked up a 6 slot courtesy of wyo with some issues in hopes of fixing it up. Have never had one of these, only 4 slots, figured it would be a fun project.

Sold as having a backup RAM error and one bad slot (when checked on a good bottom board).

Things I noted when I got it:

•Battery had been removed, coin cell holder in place and 470 resistor removed.
•Z80 had been replaced and socketed.
•Slot 3 has some plastic that appears melted and pins that do not move freely.
•There are a few dabs of glue or something protecting a few traces that have some wear on the board bottom.
•Some gorilla must have ripped the memory card cables out because three of the four tabs are gone, plastic is broken.


The board has some kind of Unibios in it. On the first boot, without a battery in place, I got this error screen.



Subsequent boots closely after would produce this screen and tick (like watchdog tick) slowly about twice per second. I would have to let it sit for a bit to get it to show the Backup RAM self test fail screen.



I put a stock US bios from a 4 slot I had in it and without a battery it actually booted to crosshatch. Although the edges were Yellow (Europe) instead of Blue for a US bios, the Soft Dips were full of garbage and it ran games in Slots 1 and 2 but they were both at difficult Level 1. I am for now attributing all of those issues to bad Backup RAM. I couldn't clear the Backup RAM.

With the stock bios still in I put a CR2032 in and this time the board booted to a Backup RAM error.



My understanding is that since the second pair of numbers is off that it is the Lower Backup RAM with the issue.

According to channelmaniac here...

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) Backup RAM Error: Address Write Read 00D01406 AAAA AA2A The Read code is broken up into 2 parts... AA and 2A The first 2 characters are the upper bits and are...

www.neo-geo.com

...6 slot Lower Backup RAM is F9

The Backup RAM chips are both Sony brand which is different than all of the others, but they don't seem to have been replaced. Wondering if that's normal.

Edit: I was looking at the wrong chips just because they were different. Backup RAM is further down...



In any case, that's where I'll start unless anyone has other tips and update after I do that.

 

[lithy]

Well, pulled one from a scrap MV4



Removed the Lower Backup RAM on the MV6 at F9



And replaced it



Still getting a Backup RAM error but now instead of returning 5551 I'm getting 5554. With Unibios or stock Bios, with or without battery. Same error.

Feels like I just pulled a bum chip from the scrap board. That board has a lot of trace damage and watchdogs so I don't really know what chips might be good or bad on it. But before I go and pull another to swap is there anything to check first?

Edit: I guess maybe it would be smart to swap the upper and lower Backup RAMs first and see if the error moves to the upper register before introducing another chip to the mix.

 

[ack]

I would double check continuity of d0-d7 between lower backup ram and lower work ram. They should be connected. Its possible whomever replaced the backup ram before damaged a trace.

 

[lithy]

I would double check continuity of d0-d7 between lower backup ram and lower work ram. They should be connected. Its possible whomever replaced the backup ram before damaged a trace.

Thanks, double checked all the connections to the work ram and they are all good.

I swapped the upper and lower Backup RAM chips and the error now displays on the first two bits (upper register). So now I'm pulling a new chip from the scrap board to try out.

 

[lithy]

Success, just bad luck I guess that I grabbed a bad RAM off the scrap board, made for a bit of extra work, but I'll chalk it up to some useful SMD practice, another handful of successful removals and installs under my belt without fucking up the board.

Booted to a crosshatch on the stock bios so I installed a battery, cleared the backup RAM and then put the slot board on and loaded it with games.



Slot 1

Slot 2

Slot 3

Slot 4

Slot 5

Slot 6


As you can see Slot 3 has some issues. As mentioned in the opening post it has some visible plastic and pins damage, I will have to investigate some possible solutions or look to find a replacement slot.

Other things to do:

The edges of the crosshatch are still yellow (or is it green?) with the stock US ver 2 bios from a 4 slot, someone will have to tell me if that is correct.

Find a metal cover for it.

Decide if I should attempt to remove the memory card connectors from the 4 slot scrap board and transplant them onto the 6 slot.

Remove the coin battery holder and relocate it to the underside of the board for easier replacement.

Test the other functions like credit displays, memory card/headphone board, EL panels (not sure what hooking it up to 4 slot ELs would do, just skip 5-6 I guess?)

For now I have a working 5 slot.

 

[lithy]

So you can see the slot damage here.

This is on the CHA top side board connector.

I attempted to push the pins away from the plastic, but still getting those lines which I think are C rom data issues and no sound. And even if I didn't, the pins are stiff and don't move back or forth easily or at all, and I would probably still be concerned with either the long term effect on the cart slot or my carts.



I will check all of the pin connections first just to make sure there aren't any trace issues, but the board looks pretty good while the slot damage is very obvious.

I have two possible sources for a replacement slot, an MV2F that I haven't got fully working yet but feels close just has some C data line issues still. Of course I also have two working MV2F boards...I could just call that one a spares board and grab one of the cart slots.

Or I have a slot board from a scrap MV1ACHX that watchdogs. In that case the slot board I think would transfer just fine to my MV1A if I ever needed it, although a failing slot seems more unlikely that BUF failures for these A boards.

Don't have any definite scrap slots yet... decisions, decisions, leaning toward pulling it from the 1 slot. Then it's just a matter of desoldering/resoldering a zillion pins.

 

[Neo Alec]

I've seen sellers on aliexpress and ebay selling just the slot part of 1-slot boards. That would be a pretty sensible source of an original slot.

You'll probably have to replace the slot. The pins can look like they're making contact, but they're really tricky.

 

[lithy]

Kids off school left me home and bored, so I took the opportunity to take the memory card board connectors off of my scrap 4 slot. One came off perfectly , the other was mostly ok but did slightly warp during removal.

It was a lot of work to get the vias cleaned up well enough after removing the more broken one on the 6 slot to be able to remount it to solder it in place.

Not the best solder work, I think I need better technique or better solder it seems like when the pins get too small it doesn't flow well into vias even with flux, it is fine for surface mount though.

I might still do the other at some point but...I need a mental break.

 

[Evan]

Really impressive work, makes me wonder why together the 6 slot boards are so failure prone

 

[Neo Alec]

Really impressive work, makes me wonder why together the 6 slot boards are so failure prone

There are more potential points of failure. 4-slot boards are similar because they are also two PCB's sandwiched together.

 

[lithy]

Really impressive work, makes me wonder why together the 6 slot boards are so failure prone

Honestly, I don't really think they're that failure prone when you compare like for like boards. Definitely as reliable as the MV4. The later board revisions (the 6 slot did not get a revision) may have improved reliability in some cases but introduced different problems too.

Granted, this is the only one that I have hands on experience with but superficial damage aside, this one didn't have anything wrong with it than many other boards do, RAM chip failures are definitely common enough.

My slot issue isn't really a board failure problem, someone just put something hot to the plastic and messed it up.

Only way you could say they're more failure prone is that like Alec mentioned, the 4 and 6 are sandwich board stacks and then for certain components on the slot board, multiply the chips by 4 or 6 and gives you more opportunities for a failure.

 

[lithy]

Today's progress was beginning prep for a new half of the slot. I figured the best course of action would be to cut the bad slot out and then I can focus on pulling one pin at a time and cleaning up the via without worrying so much about trying to pull a 120 pin connector all at once.

So after some careful (and admittedly some not so careful) Dremel work, prying, and using a butter knife to guard the other half of the slot from cutting too deep, I got all but a small bit of each pin cut out and removed all of the plastic.

Cleaning it all up to be ready for the replacement slot will probably take longer and be pretty monotonous but I'm hoping it won't be as stressful as the cutting.

 

[lithy]

Getting closer...

Progress for tonight, last weeks pinewood derby car paint bay became a makeshift PCB stand so that I could use the desoldering gun on one side and pull the pin out on the other.

Got half of the pins pulled and got the vias cleared and ran through with some of the thin rods the desoldering gun came with that have a light file on the end. By the end I had a pretty good process going.

Tried to be as patient as possible, stopping to clean out the desoldering pump a couple times during the process. Still marked a few spots on the solder mask but happy enough with it.

 

[max 330 megafartz]

Pulling an entire slot seems impossible, but here you are halfway through doing one. Dont even understand how you are getting the leverage when 60 other pins are still soldered in place

 

[lithy]

Pulling an entire slot seems impossible, but here you are halfway through doing one. Dont even understand how you are getting the leverage when 60 other pins are still soldered in place

Nah, see the pic in post #12. I dremeled the whole thing off at the legs so that I can just deal with one pin at a time.

 

[max 330 megafartz]

Nah, see the pic in post #12. I dremeled the whole thing off at the legs so that I can just deal with one pin at a time.

Genius. Ok that makes sense. Gotta remember that if i need to cart slot swap any other game system (including a neo, of course)

 

[lithy]

Finished removal.

 

[lithy]

Small things for today, nothing important just jabbering to myself to document details.

I pulled up the coin battery holder that was there so that I could use the ones I like which are a bit sturdier and put it on the bottom of the board for a change out without disassembling the board stack. The battery rot is not pretty but not too bad, that one trace right by the positive lead looks sketchy but it checked out. Not sure what it carries but if I ever have issues I can remember to check that one. I know some people don't recommend it but I like the rechargeable ML2032. So I also added a 470 resistor back.



Also went to investigate screws. I have 10 PCB feet and standoffs which I think is correct but missing other screws.

Pretty sure no one cares, but I believe the shorter brass screws for the PCB feet on the edges are M3x10 with a split washer and flat washer. The longer brass screws that go through the cart slots to the PCB feet are M3x15. Then the screws through the board to board connectors are M2.5x25 with a thin nylon washer and M2.5 hex nut.

Lastly, I had an early build 4 slot cab that came with the reset button and jumper wire from top to bottom board. Unfortunately that bottom board was not fixable, but I was able to use the slot board and get a different bottom board working but it didn't have the reset or jumper (thread with info is in this forum somewhere). But that bad bottom board became my parts donor that gave some parts for this six slot. So anyway, I had this wire, I know it isn't really required, but I thought it would be cool to put on since it had the jumper posts.

 

[lithy]

After posting about my options for a replacement slot, nuke sc reached out and said he had a spare slot board and importantly, a hot plate to facilitate removing it easily-ish.

The 'sc' must stand for Santa Claus because a few days later, I had a very tidy pair of slots as a belated Christmas present. As much fun as it was for me to Dremel my melted slot off and then remove each pin one at a time, I had at least mild doubts about how successful I'd be pulling one from the boards I had.



Soldered a replacement into place, I neglected taking a picture of my solder work before screwing it back together for testing and I'm too lazy to pull it back apart now. Let's imagine it was near factory perfect. In reality, I'm sure it was perfectly mediocre. If I started this project now after this much practice everything would probably be just a little bit better than the work I did.

Due to the board flexing a little on me, and despite having my 8 year old push down a little while I soldered the first few pins, the slot was just a hair higher than completely flush on one side. I don't notice anything worrying when inserting carts, so perfect as the enemy of good and all that, I'm not going to desolder and resolder to address it. And I actually tried to take a photo and couldn't even make it look noticeable in a picture, so it seems pretty inconsequential.

Loaded up a full complement of games again and got good picture and sound on the first try on every slot but most importantly from Puzzle Bobble/Bust-A-Move in Slot #3, then switched Garou into that slot (wanted to make sure I was using as many of the pins as possible and figured that was my best choice). I did have to reseat Garou once and then Last Blade in Slot #2 (probably bumped it), but after that everything fired up. Everything looks perfect to me.



Games running on slot #3


Seems to be a working 6 slot. I still have things I want to do and test on the board but the cab I stuck it in for testing currently doesn't have EL panels, LED displays, or a Memory Card/Headphone board. I have no real reason to think they won't work, but they'll have to be tested later anyway.

Thanks again to @wyo for letting me get this to tinker with and huge thanks to @nuke sc for the hugely helpful parts assist.