MVS-4 Work RAM error

TobyPC

n00b
Joined
Dec 8, 2014
Posts
48
Hello peoples of the tech support forum. To my dismay, I powered on my lovely MVS4 to play some rounds of my favorites..and I was met with the horrible error "Work RAM Error" :annoyed:

Address: 00101408
Write: AAAA
Read: AABA

I tried to clear the backup memory by flipping all the dips to "off" and booting the board. No dice. Same error comes up.

Does anyone have any tips to correct this? I don't have a logic probe..just a multi-meeter. :(

Any help is much appreciated!
IMG_20170109_190350.jpg
 

aha2940

AH, A, COLUMBIAN!,
Joined
Dec 15, 2013
Posts
2,528
it can be a trace to the lower RAM chip or the chip itself. It's likely easy to fix if you know how to do it (solder SMD chips and stuff).

Regards.
 

Xian Xi

JammaNationX,
15 Year Member
Joined
Dec 1, 2005
Posts
27,748
Since it's AAAA instead of 5555 it's the complete opposite of what it should be, even the address is weird. I'd try replacing the main video RAM.
 

TobyPC

n00b
Joined
Dec 8, 2014
Posts
48
What kind of video RAM should I use? Or where to get the chips/where are they?

I've done soldering to PCB's in the past but I don't have much more than a Hakko soldering iron these days. My preheater was busted in a move and I'm not sure what happened with my heat wand.
 

TobyPC

n00b
Joined
Dec 8, 2014
Posts
48
I know its been almost a year, but I finally got the chance to fix it. The problem was with the lower work ram.

I was able to isolate the work ram by using a continuity tester. I probed Pin28 on the RAM chip (+5) and the +5 on the edge to verify either video or work ram. Backup ram would be tied to the battery circuit.
The video ram traced to the LSPC chip, which is how I ruled out those two.

Replaced the upper and lower work ram and TADA! Boots up perfectly. :buttrock:

rams.jpg
machine.jpg
 

TobyPC

n00b
Joined
Dec 8, 2014
Posts
48
Thanks! If you look at the lower chip you can tell I kinda goofed a trace. Not a problem this time but next time the ram fails ill be sure to have a trace repair kit handy.
 
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