Snow Bros Repair Logs

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Repairer: Paul Swan

BOARD NO: 0036
GAME: Snow Bro's
MANUFACTURER: Toaplan
DATE: 1990
HARNESS: JAMMA

SYMPTOM (02/11/96)



"COLOR RAM ERROR" reported at power on.

SOLUTION



Looking at the board and working back from the RGB edge connectors suggested that the three resistor packs RA3, RA4 and RA5 formed the colour D/A. These in turn were fed from IC11 & IC12 (74HC273) which were in turn fed from IC13 & IC14 (6116 SRAMs). The data bus for the two SRAMS were buffered onto the processor bus by IC15 & IC16 (74LS245) next to the SRAMS. With a pulse injector set for 0.5pps, the processor was reset and each pin of each SRAM data bus examined with an oscilloscope. This revealed two pins on the SRAM side that were always low despite a high present at the input of IC15 (74LS245) when enabled. Replacing IC15 (74LS245) brought back more colours but still left a "COLOR RAM ERROR". Removing the program ROMS to kill the processor and powering up leaves the SRAM contents in a random state with the only the video cycles running and makes it easier to see what is happening. Checking the data bus of IC14 (6116 SRAM) suggested one data bit was always low. Since this could have been due to a random power up effect in the SRAM, the pin was checked after three power-on cycles and in each case it was always low. Replacing IC14 (6116 SRAM) fixed the game.