Had this original Double Dragon II – The Revenge in my faulty boards pile so I deciced to take a look it hoping to fix it and complete the trilogy in my collection:
Once powered it up I was greeted by this static garbage screen:
A static screen is a clear sign of some trouble in the main code execution.So, for first, I went to dump the program ROMs and found a bad device which game me different checksum at each reading.Since my ROM set was an undumped japanese one, I was forced to convert my board into the US set which is available.This did not lead to any improvement so further investigation was needed.When I removed the EPROMs, I noticed that the socket @IC63 (the one of the bad EPROM) was oxidized:
I decided to replace it.When , before installing the new one, I was checking all the connections, I found an eaten trace underneath which should have tied pin 2 of the 74LS138 @IC64 (which generates the /CE signals for program ROMs) to pin 9 of a 74LS273 @IC71:
Once restored the connection board finally booted up but with severe sprites issues and corrupted/missing sound FXs:
Probing RAMs on video board I found some data lines stuck low on a TMM2015 @IC83 :
This was due two broken traces on solderside which I promptly patched:
This improved a little the issue giving back the missing lines to sprites but they were still wrong and garbled.Looking at MAME source, I could figured out that one of the two Z80 (the one @IC50) on top board is used as sprites CPU which takes data from a 27512 EPROM @IC37 and write/read them on a 6116 SRAM @IC24 :
Probing this static RAM (actually a Sanyo LC3517BSL compatible with 6116) revealed weak signals on its address bus:
Once removed the chip, it failed when tested out-of-circuit:
With a good RAM chip all the sprites were correctly restored :
So I moved to troubleshoot the sound FXs issue.Samples are played by an OKI MSM6295 @IC74 with takes data from two 28 pin 1Mbit MASK ROMs @IC39 and IC40:
Probing the two MASK ROMs revealed that data came out when requested so the problem had to be in the OKI MSM6295 chip which played them badly.I removed it :
and put back a good one:
This restored ADPCM samples.Board 100% fixed and board trilogy complete!