Euro League Repair Logs

From Arcade Otaku Wiki
Jump to: navigation, search

Repairer: Paul Swan

BOARD NO: 0012
GAME: Euro League
DATE: 1990

SYMPTOM (21/04/96)

(1) The bacground was split in two and duplicated.
(2) Some control inputs didn't work.


(1) Flexing and tapping the board had no effect. Using the pulse injector on the various ROM data pins revealed that the background was contained in the long strip of ROMS down the right side of the board. The upper address lines for these ROM's were generated from two 6264 RAMS in parallel with the lower ROM address lines and RAM address lines coming from a collection of LS153 multiplexors located below the RAM. All the RAM address lines were pulsing. Looking deeper into the circuit revealed that one arm of the multiplexor came from some LS374 latches fed from the CPU. This was so the CPU could update the background RAM. Another input to the multiplexor came from a colection of LS283 adders. One side of the add came from a LS374 latch fed from the CPU. This was so the CPU could scroll the background. The other side of the add came from some F169 binary counters and elsewhere on the board. This was the base video timing counter. The exact nature of the fault indicated that the duplication was unaffected by the screen scrolling in any direction. This fact implies that any address error must be before the scroll add takes place, such that the error is propagated. This is born out by the fact that all the RAM address lines were running. Since the forground was unaffected, and both forground and background usually share the same count reference, this put the fault at or near the adder inputs. A quick check with the continuity tester revealed that the A-side add inputs were fed from the video counters. Checking the A-side inputs of all the adders revealed that pin A4 on "adder 1" was always weakly high. It was possible that it was supposed to be pulled high but a quick check with the multimeter indicated the pin was floating. Whilst following the input trace back to the source, some slight and very locallised damage to the trace was found (the PCB was of the lowest possible quality). Adding a wire link to replace the trace fixed the video.

(2) A LS245 near the JAMMA connector had blown some of it's cover off. Replacing it fixed the inputs.