Neo-Geo MV1FZ (Video Ram Error 8000 region)

[Asure]

Got a MV1FZ with video ram error, decided to give it a go with all the info out on the net.
On this board, the video ram is a pair of CXK5814P-35L rams from sony. You can check which one is bad by a short-circuit on pins 13-14
The error should change depending on your short. In my case, write 5555 read 5500, this means the lower ram is bad.
I already did a 'finger' check, and indeed RAM7 was getting a little bit hotter than RAM8. Let's verify that indeed the upper ram is good, and short the bus:



Indeed, the 55 changes to 5D, so my short causes bad reads on the upper. Let's do the same on the lower ram:



Aha! No changes at all! This ram isn't returning any data on the bus.. so it must be dead!

Next step:
- Check traces for the lower ram, compared to a working MV1FZ
- Score a replacement ram! (2048x8 sram, 35NS)
- Note to self: Replacement parts for CXK5814P-35L : TOSHIBA TMM2018AP-25/35 (maybe others? Need 35NS or lower..)

To be continued..

[KmanSweden]

Cool. Good luck with the repair.

[Asure]

Update: Desoldered the (probably faulty) ram. Test now comes back as write 5555 read 55FF.
So a missing RAM or no +5V will probably get the same FF result on other boards as well

[Asure]

Got my new rams today (buyicnow) and she works again!



The ground plate was pretty damn hard to solder, and my solder sucker failed numerous times to get the solder out.. So i cheated and soldered that pin with no socket, and cut one hole from the socket rail

[Elgen]

[quote="Asure"]Update: Desoldered the (probably faulty) ram. Test now comes back as write 5555 read 55FF.
So a missing RAM or no +5V will probably get the same FF result on other boards as well :)[/quote]
That's properly because of pull-ups...