Feb 102018
 

Still another “portughese” PCB, a Sunset Riders :

The board was unstable, most of times it didn’t boot and kept resetting (watchdog active), some times after some reboots it got past the self-test and entered in game but sprites were missing.If I pressed/flexed the board, they appeared.Here’s a video for a better understanding:

I noticed someone previously tried to fix this issue by reflowing the two sprites generator ‘053244’ and ‘053245’  (forgetting to remove flux residuals )

The reflow was done properly but it was not enough, anyway there was for sure a bad contact in this area. At a closer inspection I found that a pin of the near ‘054358’ custom had its pad detached from PCB, this caused intermittent contact with its trace.Here’s a close-up under a microscope:

I promptly restored the connection, in this way the board booted all the time with sprites too.But playing the game I noticed some little glitches :

The glitches got worse if I put my fingers on the solder side of the two palette SRAMs (2K x 8-bit devices)

The one @14D was already replaced and socketed, probing the other one @13D with a scope revealed unhealthy signals on some data pins  :

This lead me to remove the device and test it ouf-of-citcuit where it failed:

Replacing the RAM fixed board completely, another successful repair in the archive.

 Posted by at 11:07 pm