Help with a backup ram error mv1fz

[giggsy07]

Hi guys.Turned on my mv1fz last night only to be greeted with the following message.
Ram Error
Address Write Read
00D00000 5555 0055
At first I could skip to aes mode and play away but now the graphics are messed up and the furthest I get is to the unibios screen with neo geo logo scrambled.I looked over the board and traces seem good although I'm no expert.No battery spillage either.Iv read posts on the forums here and got a lot of info but just to be sure id like some input before I start to attempt removing and replacing chips.Is this a case of replacing ram chips?Thanks guys

 

[giggsy07]

Anyone pls?

 

[bustedstr8]

Like you said an error at 00D00000 is almost always corroded traces from the battery. If yours checked out I would probe the /WE /OE and /CE of the lower backup ram 62256 first before changing it. There could be other problems in the circuit like a bad LS32 or something.

 

[giggsy07]

Cheers dude thanks.I noticed this now I must have missed it earlier and am wondering if this could be the culprit?

 

[bustedstr8]

That trace above U17 lookes wasted. Check the resistance between the chip and the next pad or via.

 

[giggsy07]

Thanks again and apologies for sounding like an idiot but how would I go about checking for resistance?I have a multimeter handy here but not a clue where to start.Again thank you for you're time sir..

 

[bustedstr8]

Select ohms and place probes onto two test point on either side of the suspect trace. A good reading is almost zero ohms.

 

[giggsy07]

Thank you bustedstr8 il get to it and post back results.Very grateful thank you.

 

[giggsy07]

Hi again.Getting 0 reading on that trace with multimeter no actual movement at all from digital clock.Rubbed the meter pins against each other to verify it was working beforehand and all seems good.Any further ideas?Thanks

 

[bustedstr8]

You shouldnt be getting zero, but it should be close. Something around .05-0.3 ohm. Make sure the meter isnt reading open or infinite resistance. Some meters will display something like OL for open

 

[giggsy07]

Hi again.00.9 from the chip to the pad along that trace.Only used the board twice purchased on fleabay as tested and working.Got stung..

 

[bustedstr8]

I was on my phone earlier....now that I see the HC32 it looks pretty crusty underneath. There could be severed traces underneath.

Use your ohm meter and the schematic below to test the traces to the connections labeled.
Also G1 and G2 refer to the 62256 rams.

 

[giggsy07]

Hi again thanks very much.I tested all and i do not know what readings i should be getting but they are reading.God this is hard

 

[bustedstr8]

If the connections all test near zero ohms thats about all you can do for now.

At this point you should probably send it off for repair or try to bypass the error with a unibios

 

[giggsy07]

Hi again.Very grateful for your help many thanks.Would you believe i gave the board a clean today and tested after.On startup i get the backup ram error but i can skip it and play away in aes mode with unibios.It just will not save any settings although calender settings are correct.Any taughts on this?I included this error page from unibios if that's any help.Love that combat tribes sig great gameThanks again.View attachment 19842

 

[Razoola]

What unibios version is that?

 

[Beharius]

My MV1B has the same symptoms except displaying
Write:5555 Read:55FB

Is there a schematic of the backup ram section for the MV1B? I checked the pin27 of the rams to the HC32. Pin 3 and 6 are connected as far as I understood.
What can be the problem?

 

[giggsy07]

Hi guys.Its unibios 3.2 from raz.Just changed the backup ram chips and same story but different error.Giving up now may get another and keep this for parts.I can play in aes forced mode.I give up 2 days probing has me done

 

[Razoola]

Ok the unibios error screen is related to the bios not getting correct information from the cart p1 ROM space, that results in the address error screen. So not only has something caused the backupRAM to fail, the reading of the game information has also failed or is failing.

Are you sure the cart sockets are clean?

You could also go into the memory viewer from the unibios error screen and scroll to address 0x100 and take a picture. Let us know what game is in the system.

Raz

 

[giggsy07]

Thanks Raz i mailed you a couple of weeks ago the guy with the broken pin but chip still workedThanks for the advice ill get on it and post back.

 

[Beharius]

It displays this without a cartridge inserted. I can't even enter to the hardware setup menu. In the AES mode, test sw doesn't response too.

 

[giggsy07]

Cart was inserted friend.Yes i to am limited in aes mode.Ah i will bite the bullet and get another.Cart slots clean as raz enquired as are all pins..Goodluck with your neo Beharius i have enough for now at least.