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Thread: MV2F - BACKUP RAM ERROR 0000 0055 (was 5555 B255 before battery replace)

  1. #1
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    MV2F - BACKUP RAM ERROR 0000 0055 (was 5555 B255 before battery replace)

    Backup RAM error 5555 B255 was what I started with, with a dead battery, and a little corrosion on the terminals.

    I replaced that battery, and now I get, "WRITE 0000 READ 0055"

    I was told to look at channelmaniacs posts, and look to the connections between rams and the CPU in resolving this.

    I found this post:

    http://www.neo-geo.com/forums/showth...kup-RAM-errors

    With info on the pinouts for the chips to the CPU. Those checked good, but the post looks like its for the four-slot, and not the 2 slot that I have. So I'm not sure if that matters.

    The rest of the pins - to the 74hC32 chip, 2 were there, and two weren't (the ones to pin 13).

    The reference there is to D10, but mine aren't there - the 74 chip is at J2, so I'm not sure if the pinouts are correct.

    Does anyone have the correct pinouts for the 2 slot from the SRAMs there? I have been looking for the last hour or so, and all I keep finding is for the one slot, or the above post.

    I dont SEE any corroded traces, but they are pretty tiny on this board. I am thinking it might be the 74HC32 chip?

    I am also told I can get a univeral bios for around $50 for this board, but I'd hate to pay that and it still have problems. (I have a working board; I want this one as a spare done CHEAP! haha)

    Heres the pinout info i used, which I'm not sure is for my board:

    "RAM___CPU

    1______43
    2______41
    3______36
    4______35
    5______34
    6______33
    7______32
    8______31
    9______30
    10_____29
    21_____39
    23_____40
    24_____38
    25_____37
    26_____42

    etc.

    There are 3 pins for each backup ram chip that are not connected to the CPU:

    lower ram:

    20_____74HC32 (13) located at D10
    22_____PRO-C0 (16)
    27_____74HC32 (8) located at D10

    higher ram:

    20_____74HC32 (13) located at D10
    22_____PRO-C0 (8)
    27_____74HC32 (6) located at D10 "

  2. #2
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    Test the gates on the 74HC32 first to rule it out.
    My YouTube channel contains some MVS repairs and stuff:-
    http://www.youtube.com/user/GadgetUK164

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    Quote Originally Posted by GadgetUK View Post
    Test the gates on the 74HC32 first to rule it out.
    I'm not sure how you mean / how to do this?

    UPDATE:

    Replaced the rams - now I get - "READ 5555 WRITE 0051" error.

    Different error, but still having problems!

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    You can test the 74 series logic with a logic analyzer probe, there should be info on how to do that on youtube and google. As far as logic analyzing goes there are probably people here more versed in that than I.

    That being said you know with back up ram usually being located near the battery you might want to test the traces around that area for continuity regardless especially since you say you had a dead battery with some corrosion. Test for power on the ram and 74 series chips that are associated with your ram. Also it must be said that since you replaced the rams recheck continuity to those pins, on a repair i did quite a long time back I goofed on a pad when soldering on a new SMD chip and didnt realize it till later and had to fix it lol.

    Best of luck.

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    The original B255 led me to suspect the 74HC32, but now you are getting 0051 which means that one bank is not being written to / read from at all (hence 00), and the other bank has lost a bit (51 instead of 55). 51 in binary is 01010001 you should have 01010101 so it would appear you've broken a connection to bit 3 of the databus on one of the SRAMs at least.

    You can test the 74HC32 with a logic probe - its a basic OR gate, if you want an basic explanation of how to test it watch this video I filmed ages ago. It's an aweful video but it gets the point across. https://youtu.be/eKCqXE8WBFQ?t=1635
    Watch from 27:15 onwards. There's a lot I don't like about that video - you wouldn't catch me with boards on the carpet anymore for example...
    My YouTube channel contains some MVS repairs and stuff:-
    http://www.youtube.com/user/GadgetUK164

  6. #6
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    Quote Originally Posted by GadgetUK View Post
    The original B255 led me to suspect the 74HC32, but now you are getting 0051 which means that one bank is not being written to / read from at all (hence 00), and the other bank has lost a bit (51 instead of 55). 51 in binary is 01010001 you should have 01010101 so it would appear you've broken a connection to bit 3 of the databus on one of the SRAMs at least.

    You can test the 74HC32 with a logic probe - its a basic OR gate, if you want an basic explanation of how to test it watch this video I filmed ages ago. It's an aweful video but it gets the point across. https://youtu.be/eKCqXE8WBFQ?t=1635
    Watch from 27:15 onwards. There's a lot I don't like about that video - you wouldn't catch me with boards on the carpet anymore for example...

    *UPDATE*

    No logic probe; bought 10x 74hc32 for a couple dollars from china and Replaced 74hc32 - no change.

    I struggled figuring out the Data lines from the CPU to the backup ram, as its not explicitly stated anywhere that I could find.

    I figured it out after a couple hours messing with schematics and pinouts and saw that D2 from the CPU to the SRAM Upper Ram was NOT there, even though it looked good. Reflowed it and then it was good.

    Tried again and finally booted! Though, booted to cross hatch even though carts in both slots.

    Figured it was a dirty slot; cleaned both with alcohol and contact cleaner. Waited a few minutes -turned it on and now - WATCHDOG OF DEATH.

    Clicks quickly (about 1x a second) with garbage screen, so I think this matches the watch dog error.

    NOTE - the backup ram lower ram had NONE of the data lines reaching the cpu from my testing for continuity. Though, I'm not sure if I am correct. Here's the testing I did:

    DATA_CPU_RAM Pinouts:

    D0_5_11

    D1_4_12

    D2_3_13

    D3_2_15

    D4_1_16

    D5_64_17

    D6_63_18

    D7_62_19


    Could it be a problem with the lower ram and the data lines? I tried reflowing them like I did d2 on the upper ram - no dice. With such a large group, Im guessing those lines got corroded or cut.

    Should I just jump them directly to the CPU pins, or would this not cause the watchdog error I'm getting?

  7. #7
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    The backup RAM will be connected on data bus I am sure - It's a case of D0-D7 going to one SRAM and D8 to D15 going to the other (I think, if my memory is working lol).

    If all you did is clean up the slots and ended up with a watchdog that's strange - maybe a short somewhere in the cart slot?? I would be tempted to test with the SMK Dan Diagnostic BIOS if you haven't already. That might boot past the watchdog and you may find you've got a fault work RAM chip or something.
    My YouTube channel contains some MVS repairs and stuff:-
    http://www.youtube.com/user/GadgetUK164

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    Quote Originally Posted by GadgetUK View Post
    The backup RAM will be connected on data bus I am sure - It's a case of D0-D7 going to one SRAM and D8 to D15 going to the other (I think, if my memory is working lol).

    If all you did is clean up the slots and ended up with a watchdog that's strange - maybe a short somewhere in the cart slot?? I would be tempted to test with the SMK Dan Diagnostic BIOS if you haven't already. That might boot past the watchdog and you may find you've got a fault work RAM chip or something.
    It is strange! I am wondering if maybe I shorted or broke something while handling it.

    I don't have the diagnostic ROM. I am checking with someone if they can burn me one in the states, as I don't have the hardware to do that.

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    No dice on Diag bios, or using universal. Still just does click of death.

    I may just end up sending this in to be looked at by channelmaniac. I'm about at my wits' end.

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    I would check WRAM connectivity and ROM connectivity before giving up. Check CPU to WRAM on address and datalines, also do the same between CPU and ROM.
    My YouTube channel contains some MVS repairs and stuff:-
    http://www.youtube.com/user/GadgetUK164

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    What pins are we talking on the CPU - > WRAM and CPU - > ROM? I had a heck of a time figuring CPU - Backup RAM. Is there a chart or somewhere I can reference this?

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    Quote Originally Posted by Spicules View Post
    What pins are we talking on the CPU - > WRAM and CPU - > ROM? I had a heck of a time figuring CPU - Backup RAM. Is there a chart or somewhere I can reference this?
    Yes, CPU to WRAM and CPU to ROM. Best to look at the AES schematics since they are clearer and easier to read and connections in those respsects will be the same as MVS.
    My YouTube channel contains some MVS repairs and stuff:-
    http://www.youtube.com/user/GadgetUK164

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