Had on the bench this Marchen Maze PCB (Namco System 1 hardware) :

On the power up I was greeted by this screen:

The RAM @D6 is a 6264 located on CPU board (fault was surely on this board since I succesfully swapped a good one) used in pair with another one @E6 , both are adressed by the near custom ’48’ which is a sprite address generator:

For first I went to replace both RAMs (sometimes the board booted showing an error also on the one @E6) but this didn’t cure the problem as well swapping a good known custom ’48’ had no effect.Probing these RAMs revealed some address lines stuck high.Looking at the schematics of Pac-Mania (which runs on same hardware) I figured out that adress lines from custom to RAMs are driven by two 74LS365 @H6 and @L6.

 

Parts mounted on the PCB were from Fujitsu which means high chance of failure:

After a quick test with my HP10529A logic comparator (which confirmed me troubles on all outputs) I decided to remove them.They both failed in my programmer:

This cleared the error on startup so board successfully booted into game but sprites were all blocky:

Judging from the kind of fault on screen, this, more than an addressing issue, had to have something to do with data.Always looking at schematics I noticed that data bits  from the custom ’48’ and RAMs are routed to two 74LS377 @A3 and @A4 :

and from these to the custom ’39’ sprites generator:

Piggybacking the two 74LS377 I could partially restore sprites :

This lead me to remove and replace both.The desoldered ones failed when tested out of circuit :

Sprites back again in all its glory and board 100% fixed!

Got this Taito Megablast for a repair:

When I powered it up, I was greeted by a solid black screen, /RESET and /HALT on main 68000 CPU were stuck high.A visual inspection revealed that JAMMA connector was oxidized.Once cleaned it, the board booted:

As you can see both tiles and sprites had sever issues, besided the sound was all garbled and scratchy:

So, for first I went to dump the devices containing tiles/sprites (three 40 pin MASK ROMs 27C400 compatible) and audio samples (two 32 pin MASK ROMs 27C040 compatible) and dumps were not matching the MAME ROM set for the ones @IC32 (sprite data), IC58 (tiles data) and IC29-IC30 (audio samples data) :

Loading my dumps in MAME I could reproduce the issues more or less accurately:

Replacing these bad MASK ROMs with the equivalent EPROMs fixed completely the game.

Another Haunted Castle repair after the recent one from Corrado.

Board was in good shape :

But it showed jailbars on sprites, besides the sound was missing :

So I started to probe the two 4Mbit MASK ROMs containg sprites data and I found a bad signal on pin 28 of the one @J5 (good on the left, bad on the right) :

I desoldered the MASK ROM and my programmer reported, indeed, troubles on pin 28 while I tried to read it :

Loading the dump in MAME I could reproduce exactly my issue :

With a programmed 27C400 as replacement of this MASK ROM the sprites were correclty restored so I went to troubleshoot the missing sound.With my analog scope I found weak signals on some data line of the 2018 SRAM @F2 (which the Z80 audio CPU accesses to) :

I promptly removed this SRAM which failed when tested in my programmer :

With a good RAM fitted the sound were restored but music was noisy and scratchy :

The FM sound generator is a Yamaha YM3812 @D5 which is connected to an external YM3014 DAC @C4.Probing its digital output  (PIN 21) revealed differences compared to the healthy signal from a good board pictured below :

So, I removed the chip and installed a good one :

This restored a clear sound.Job done, board 100% fixed!