Neo Geo 4 slot Video Ram Error Repair?

If you post the error code, someone on the NegoGeo forums can tell you which chip is the issue. These are surface mount, which is a bit tough, but manageable even without hot air device.
 
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Neither cab worked at all; only 1 had any picture, and the display showed a video ram error. The other PCB was also failed with a backup ram error. I immediately cut the stock backup battery out of both PCBs and fortunately, neither showed signs of acid damage.

View attachment 589004

My first goals were to take inventory and source parts that couldn't be repaired. Both cabs had K7000 19" monitors, Beta had a k7000-A variant. While this variant is somewhat maligned because of a un-obtainable flyback, my personal experience is that the construction of the this variant is a bit more robust. Probably why this monitor was working, while the vanilla k7000 was not.

I gave both PCBS a good cleaning. Right away I noticed some corrosion in the backup ram area on the "B" cab PCB. A scrubbing with some IPA resulted in a functional PCB! It was a much-needed early win! Unfortunately the next day it threw up the same backup ram error, so I did some continuity testing and discovered a faulty trace, which I repaired and the board worked great!

View attachment 589005View attachment 589006
The other PCB was a different story. With some help from the folks at the neo-geo forums I identified the faulty video ram chip from the error code. After replacing the ram chip, we are 2 for 2 on PCB repair!

View attachment 589007
I turned to both monitors, which were mostly the normal K7000 repair issues. Cap kits for both, the regular 7000 needed extensive reflow and work in the power section (pretty standard), reinforcing r89,101, etc. The flyback was a white knobbed version which had a bad focus pot, so I replaced it. Unfortunately this tube had terrible emissions and a heater to cathode short on the blue gun, so I decided to retire this tube. Many thanks to @Slackmoe for the tube hookup.

Beta's tube was also in a similar state, so also underwent a tube swap. The K7000a chassis was rock solid in all the weak joints, so no major rework needed. Just a Cap kit and a good cleaning!
 
Copy and Paste from here. https://wiki.arcadeotaku.com/w/MVS_MV-4_Repair_Logs

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

Video RAM Error:

Address Write Read
00000607 5555 5455

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

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

Work RAM Error:

Address Write Read
xxxxxxxx AAAA AABA

(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
 
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