MV1B - Missing vertical lines on certain layers (Potential RAM issue?)

[MooThing]

Hi there, apologies for my first contribution here being begging for support but I figure it'd be hard to contribute without a working system of my own.

I own an MVS-MV1B in relatively good condition, I've made some modifications over the time I've had it such as replacing the BIOS and clock battery as well as making the board horizontal in preparation for consolizing it later down the road.

However at the moment it has an issue with alternating vertical lines in certain layers of the image not being rendered, you can see this in the following shots of Metal Slug (with what's meant to be the Universe BIOS menu over the top) and the ROM selection screen for the 161-in-1 cartridge (the background around Terry is supposed to be black). I believe this is due to a stuck bit on one of the WRAM/VRAM chips however I'm unsure which ones on the board are responsible for what. If anyone can point me to which chip may be faulty I'm totally okay with replacing it. Thanks!

 

[littlecharlie]

Have you tried to put a diag bios to check if it reports any specific error?

Neo Diagnostics homepage

 

[MooThing]

Have you tried to put a diag bios to check if it reports any specific error?

Neo Diagnostics homepage

I should definitely give that a shot, I'll either erase my unibios chip or try and source another M27C1024 locally.

 

[maki]

I've made some modifications over the time I've had it such as replacing the BIOS and clock battery as well as making the board horizontal in preparation for consolizing it later down the road

If you used the flex PCB to replace the connector/plug, check every single trace to and from it, good pics might help.

The error you're seeing could be caused by a bad flex PCB.

 

[Xian Xi]

Fix layer, most likely a bad 245.

 

[Neo Alec]

I would love to have @Xian Xi come around more often for the lightning round.

 

[MooThing]

If you used the flex PCB to replace the connector/plug, check every single trace to and from it, good pics might help.

The error you're seeing could be caused by a bad flex PCB.

I replaced the main PCB's connector with the appropriate JAE TX25 right angle receptacle. This was an issue that persisted even before replacing them so I'm not too concerned about that being the cause.

Fix layer, most likely a bad 245.

From what I've read, that would be either RAM5 or RAM6, correct? My suspicions were one of those two as pressure/heat applied to seemingly either one of those chips would affect the layer for better or worse.

 

[ack]

From what I've read, that would be either RAM5 or RAM6, correct? My suspicions were one of those two as pressure/heat applied to seemingly either one of those chips would affect the layer for better or worse.

Video ram doesn't contain graphics/pixels data. It just has details about where graphic elements should be placed on screen. One of the larger chips takes that data and uses it to render the screen pulling the actual pixel data from the C and S1 roms on the cart. This is why Xian Xi is suggesting it might be a 245 since it appears to be a data path issue from the C or S1 roms.

 

[MooThing]

A quick update: I reflowed the GRC2 and the issue seems to have disappeared (for now). I'll give it a good long run to see if it reappears.

 

[MooThing]

Think it's safe to say it's all good now, hopefully this'll help someone else years down the line.