This game had two problem:
Given the high unreliablity of Taito maskroms I immediately tested the ones marked in red which with no surprice some pins not connected internally
C49-04 restored the glitchy sound and C49-02 fixed the blocky gfx.
Replacements to be used are 27c400 (4mbit eproms with maskroms pinout)
Game 100% fixed
Got this game for a repair which had all screen with washed out colours
This game has a SEIBU custom named UEC51 which is used as a DAC to output the RGB colours on the monitor.
The input pins were good, but a couple of output pins were fixed, thus creating the images as they had less shades of colours.
I took a good one from another Toki which had other faults and the problem was fixed 100%
The game had two problems.
First one was the music that sometimes when switching on the game was glitched (very fast tempo or corrupted voices)
The first problem was fixed by replacing capacitor C7 which was used to reset the chips and didn’t work correctly.
Second problem was some black pixels on some elements of the background.
After shorting some data lines of the gfx maskroms I found the one responsibile for the background images.
Normally when a markrom fails you get blocky graphics. In this case was only some bad pixels.
Looking on the solder side of the pcb I immediately noticed one pin of one address line of the background image markrom touching the network resistance beside which forced the address line to 1.
Disconnecting it solved the problem
Received this game for a repair.
The game had messed background images
Shorting some data pins rams I found the one responsible for the tiles arrangement.
I replaced the one marked in red below and it was infact faulty but it didn’t fix completely the problem.
I noticed that the 74ls745 above it was pressed down badly like if it was hit but something.
I decided to unsolder it and test the continuity of all the pads and infact I found three of them (marked in red) that visually were OK but they had no continuity
with the other chips.
That meant that the internal pad was broken so bad it detached internally
Making some ugly flying wiring with something I had at hand I tested the game which was fully restored
Yes, yet another Double Dragon PCB on the bench.
The board was in good shape:
but it didn’t pass the self-test sitting on a ‘63701 ERROR:
The /HALT line of the HD63701 MCU was asserted, this was sign of some trouble in its busses.I swapped a good chip with no change so I went to look at schematics.All was good until I found no continuity between the address line ‘A0’ (pin 50) of the MCU with pin 3 of the 74F157 @IC8:
Tracing back the address line I could figure out where connection was interrupted, exactly under the 74F157 @IC7 so I removed it.Inspecting the involved area with a USB microscope revealed a corroded trace :
I patched it with some AWG30 wire:
With this fix finally the board passed the self-test but two issues were present in game : sound was missing and backgrounds had jailbars :
The first issue was due a missing 10Kohm potentiometer in the sound section:
The backgrounds GFX data are stored into four 27512 OTP devices on video board :
When I went to dump the ones @IC108 ans IC109 my programmer warned me about a bad contact on pin 19 (data line ‘D7’) of both :
Obviously the resulting dumps didn’t match the ones from MAME ROM sets so I programmed two 27C512 EPROMs as replacement.This restored graphics completely.Yes, yet another Double Dragon PCB fixed!