Got a mint Mystic Warriors PCB for repair (an action game released by KONAMI in 1993) :
On power up the POST reported many bad devices :
In the details the devices @5F-3F-5D-7D-6B represented almost the whole sound system :
- 5F = first '054539' PCM 8 Channel custom chip
- 3F = 32K x 8-bit SRAM
- 5D = second '054539' PCM 8 Channel custom chip
- 7D = 8K x 8-bit SRAM
- 6B = Z80 ROM (27C010)
The sound system is ruled by a Z80 CPU (Z80E in this case)
When I went to probe it I found all the outputs (address and system control lines) were silent, this could be a sign the CPU is internally faulty hence I desoldered it :
I tested the CPU on another board and I had confirm it was really fauty so I replaced it :
With a good CPU the board passed the initial test but the screen was yellow tinted :
A yellowish screen means the blue color is missing.The signal is generated by one of the three '054573' custom SIL (one for each RGB color), the one @U50 :
Tested the output with a logic probe revealed a stuck signal :
I removed and replaced the component with a reproduction of mine :
This fixed the lack of blue color and board completely.Another repair accomplished.
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