Sky Soldiers Graphics Issue

tuco

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I have a sky soldiers which works perfectly apart form the graphics being a little corrupted.
On switch on I get the screen shown below -
which is followed by two more screen which match a 100% working board.
I know from a friends 100% working game that it should be a completely white screen.

The actual graphics fault is tricky to explain but the best description is little dark squares pattern effect. It is best seen in the title screen - click to open in another window and look in the lower left and right corners of the image. It's like darker squares surrounded by lighter horizontal and vertical lines.
See the image below with the name "sky soldiers"

I checked all ICs relating to video RAM and only found one faulty. I replaced it but no change.

Comparing my board to a 100% working board the only difference I found was around the 8 CXK5814 (6116) RAM chips. On the working board all the I/O pins are chirping away when probed, on my board the higher numbered I/O pins (I/O5,6,7,8 - Pins 13, 14, 15 and 16) on every second RAM chip have some pins chirping, some low and some high. Looking at the board they don't seem to go anywhere but then neither do the Vcc and GND pins on the RAM chips. Surely it's not a triple layer board.

One RAM chip had I/O 5,6,7 and 8 (Pins 13, 14, 15 and 16) all solidly high or low. I changed this chip and you guessed it, no change.

Any ideas other than removing all RAM chips and replacing them?

Does anyone have a schematic?
 

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Those Sony chips are very suseptible to power surge damage. You'll need to replace 'em to find which ones are causing the signals to look funky.

The hard part is that they are very fast chips so most generic 6116 chips won't replace 'em. A -35 is 35ns and NOT 350ns. You can find them or some fast 2018 chips on the color RAM bank of a CPS1 board. If you have a CPS1 board with bad video RAM it would be a good donor board for those color RAM chips.

One thing you can do on them is to look for chips that are darkened on the center of the chip from internally generated heat. That's one easy way to ID which ones of those Sony chips may be bad. They are used as Sprite RAM on the Neo Geo boards and dark spots are an easy way to spot 'em. ;)

RJ
 
this is all to weird..... i just picked one of these up in a converted kangaroo cab.. it is doing the same thing.... interested to see what fixxes it...
 
Those Sony chips are very suseptible to power surge damage. You'll need to replace 'em to find which ones are causing the signals to look funky.

The hard part is that they are very fast chips so most generic 6116 chips won't replace 'em. A -35 is 35ns and NOT 350ns. You can find them or some fast 2018 chips on the color RAM bank of a CPS1 board. If you have a CPS1 board with bad video RAM it would be a good donor board for those color RAM chips.

One thing you can do on them is to look for chips that are darkened on the center of the chip from internally generated heat. That's one easy way to ID which ones of those Sony chips may be bad. They are used as Sprite RAM on the Neo Geo boards and dark spots are an easy way to spot 'em. ;)

RJ

Interesting - The 6116 I used as a replacement is UM6116K-3 which has a 90ns access time. It's from an old raiden board.
No chips on the entire board are hot and none are burnt. All chips (apart from RAM chips) have the same outputs as my friends 100% working sky soldiers.

I was hoping to avoid removing the 8 sony RAM chips. Our chip desoldering iron at work has stopped working so I'll have to resort to the slow method.

Also interesting that another board has the same fault!
 
this is all to weird..... i just picked one of these up in a converted kangaroo cab.. it is doing the same thing.... interested to see what fixxes it...

Bad SRAM at L6. When do you want to drive over and pick it up?
 
I was hoping to avoid removing the 8 sony RAM chips. Our chip desoldering iron at work has stopped working so I'll have to resort to the slow method.

I simply powered the board up cold and used the back of my finger between the 2nd and 3rd joint to feel the top of each SRAM. One was getting hot while the others were still cold. That's the one at L6 I replaced to fix Trey's board.

The back of your finger is MUCH more sensitive to temperature differences than the tips.

RJ
 
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