Aug 012016
 

A quick fix for a PCB that seems to develop always same issue judging from my experience and other repair logs.Received this Snow Bros for a repair:

DSCN3977

It was playing fine but some sprites suffered from flickering (it’s hard for my camera to capture this, see from second 5 of below video)  :

Maybe you can understand better from this picture provided me by the PCB owner:

snowbros02

The sprites are generated by the Pandora custom chip which read data from a MASK ROM and write them to four 4464 (64K x 4bits DRAMs) :

sprites_circuitry

When I went to probe these dynamic RAMs with my scope all was good except one data line (D2, pin 3) of the one @IC24, signal was weak and stuck high compared to an healty one:

data_line_4464_IC24_comparison

Confident I removed the chip which failed when tested out-of-circuit:

41464@IC24_failed

Installed a socket for a fresh chip:

DSCN3980

and tested again the board:

DSCN3981

No more sprites flickering and game 100% fixed.

 

 Posted by at 10:19 pm