Xain'd Sleena Repair Logs

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Repairer: Paul Swan

BOARD NO: 0009
GAME: Xain'd Sleena
MANUFACTURER: Technos
DATE: 1986
HARNESS: JAMMA

SYMPTOM (21/04/96)



(1) The background had black virtical bars down it.
(2) The forgound colour was corrupt.

SOLUTION



(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 block of eight ROMS in the corner of the video board. Some investigative work with a continuity tester revealed that the address lines for the ROMS were all commoned together and the data bus for each row was commoned together, giving a 16-bit background video bus. The nature of the fault strongly suggested that a data bit was down somewhere between the background ROMS and the plane mixing logic on the data bus. Further investigation with a continuity tester indicated that the background video bus is fed directly into a bank of four LS194 shift registers. This implies that the video mixing is done after the data stream is serialized, and there seemed no viable theory for how this fault could be created on a serial bit stream. Using the pulse injector on the ROM data pins revealed that all the data bits of "ROM bank one" affected the background and that bits 1 and 5 affected the corrupted column. All the data bits of "ROM bank 2" affected the background with the exception of bit 1, which had no effect. Additionaly, bit 5 of this bank affected the corrupted column. Data bit 1 of "ROM bank 2" was selected as a candidate for further investigation. Tracing this data bit with a continuity tester revealed that it went into the first shift register and had a resistance of 10 ohms to Vcc. Pulling all the ROMS out of the bank eliminated the 10 ohms to Vcc from the circuit. Checking each ROM in turn identified IC133 (ROM PN-0) as having the 10 ohm to Vcc fault. Checking this EPROM in a programmer resulted in an image in which bit 1 was always set. Attempting to blow out the low resistance resulted in a bright flash and distroyed the device completely. The game should work OK when a new EPROM for this location is programmed.

(2) Tapping the ribbon cables had an effect. Replacing the ribbon cables fixed it.