Double Dragon (bootleg with 3xM6809) repair log

Some days ago I receved for repair this bootleg of Double Dragon.The PCB is made of a CPU board :

 

 and a VIDEO one :

It's a 1:1 copy of the original hardware with the exception of the HD63701YOP MCU which has been replaced by a 6809 CPU (bringing the number of these CPUs to three) plus a RAM, a ROM and a PLD.

I powered up the board and it booted up, game was playable with sound but sprites were affected by jailbars :

I repaired different of these boards so I knew this is a common failure which most of times is caused by a bad RAM on VIDEO board.Specifically there are two 2K x 8-bit static RAMs (2018 or 6116) that are part of the line buffer.I probed them with a scope and found some unhealthy signals on some data lines of the RAM @5M :

 

You can see on below picture a comparison between a good signal (on the left) and a bad one (on the right)

Sure enough I removed the suspicious RAM :

 

It indeed failed the out-of-circuit test :

 

I installed a good RAM on a machine-tooled socket :

This fixed the sprite issue and board completely.Another successful repair.

Gang Wars repair log and 'ALPHA-8921/PRO-CT0' reproduction

Some time ago I've been sent a Gang Wars PCB for repair.For the uninitiated this game is a beat 'em up developed by Alpha Denshi and published by SNK in 1989.The board was in fair condition (a little bit dusty perhaps...) 

 At power up I was greeted by a static garbage screen :

 

Checking the program ROMs with a logic probe revealed stuck data lines :

At visual inspection I found that one the two SIL custom ICs marked 'ALPHA-INPUT87' was missing :

 

Time ago I made replacement of this part therefore I know that it's used for inputs and it's connected to 68000 main CPU data bus.I promptly installed the reproduction :

The board finlly booted but backgrounds had jailbars through :

Graphics data are stored onto four 4Mbit MASK ROMs :

Checking them with a logic probe revealed that pin 19 (data line D3) of the one @16J was stuck low :

 I traced the pin back to the SDIP64 custom IC marked 'ALPHA-8921' :

After a quick research on the net I found that the 'ALPHA-8921' can be found also on NEO-GEO hardware but under different part name, specifically as 'PRO-CT0' on AES cartridges and 'SNK-9201' on MVS boards.Regarding the functions of this chip, it can be used as graphics muxer on Alpha68k hardware and security device on NEO-GEO hardware.

The chip on my board was likely faulty so I removed it and installed a SDIP64 socket :

 

I borrowed a 'SNK-9201' from a Fatal Fury 2 MVS cart :

 

This fixed the graphics so this confirmed that my chip was really bad :

 

The repair was done but, since 'furrtek' during his NEO-geo development made schematics of this custom IC (thanks to him for his always brilliant job!) , I decided to design a modern replacement :

 The reproduction was succesfully tested on the Gang Wars PCB and Fatal Fury 2 MVS cart :