May 122016
 

Received this Batsugun Special Ver. PCB for a repair:

Batsugun_Special_ver_Japan_PCB

Game played fine but colors were all dull and washed-out, take a look at this comparison with a MAME snapshot on the left:

colors_comparison

or this video:

This was a clear sign of some troubles in colors palette circuitry.After studying the hardware, I was able to locate this section by shortcircuting some address/data lines of two CXK5816 SRAMs @U39 and U40 and at the same time observing  color changes on screen:

palette_circutry

Besides the two mentioned SRAMs, you can see some 74LS245 and two 74HC273 involved in data bus (the first ones in exchanging data from/to the two RAMs, the latter in latching).When  I went to probe the two 74HC273 I found that input pin 13 of the one @U43 was stuck low  and its corresponding output pin 12 showed only weak signals:

74HC274@U43_probing

So confident I went to remove it:

74HC274@U43_removed

When I tested it out-of-circuit it failed:

74HC273@U43_failed

Once fitted a good IC and powered up again the board, the game played great with no further issues.

fixed

End of job.

 Posted by at 11:27 pm

  One Response to “Batsugun Special Ver. repair log”

  1. You da man!
    Good job as always!