Received from Portugal a batch of faulty PCBs for repair, there was among them this Bomber Man World (on Irem M97 hardware)

The PCB was working fine except for the sound, you could only hear some scratchy noise and also video output was affected showing some kind of disturbs:

This is scenario I faced many times during repairs and the cause was always the same : the electrolytic capacitors.In particular Irem boards suffers from the “brown ELNA” syndrome and this was not an expection.I  went to measure capacitors with my ESR meter starting from the 470uF 25V one @C203 which filters the +12V routed to to sound amplfier.My meter didn’t display any reading meaning the measured ESR value was out of range (from 0 to 99 Ohm on my meter) 

Probing the +12V line with a scope confirmed there was some ripple (no longer filtered by this capacitor)

The out-of-circuit testing  confirmed the high ESR and bad capacitance :

Fitting a good capacitor restored loud and crisp sound.End of job.

Received from Austria this faulty Kuri Kinton PCB, an obscure fighting game manufactured by Taito in 1988 :

Board is very compact, hardware platform is called ” Taito L system” based on the the ‘TC0090LVC’ (a custom Z80), an all-in-one  CPU/system controller  which does everything  (game logic, tile handling, sprite handling, I/O handling, etc).At power up I was greeted by this scenario:

The game played almost blind, you could coin up but graphics were all scrambled.Ruled out the two GFX 4Mbit MASK ROMs, very few was left to probe.There are four 62256 SRAMs (32K x 8-bit) whose data/address busses are tied to the ‘TC0090LVC’ :

Probing them revealed unhealthy signals on data lines of some of them:

I decided to remove them all :

Actually only the ones @IC9 and IC10 failed the out-of-circuit testing:

Replacing them fixed board completely.End of job.

Received from Spain this faulty Vulcan Venture PCB (export release of Gradius II on the glorious’ Konami Twin16 hardware) 

This is what I got once powered it up:

Graphics were all corrupted, you could barely recognize the self-test procedure which failed all the time causing the reset of the whole system in an endless loop.I focused my troubleshooting on VIDEO board:

Like the CPU board, also the VIDEO one was almost fully populated with Fujitsu TTLs  but before going thru them I started to probe the various RAMs.I found one 62256 @8L with dead outputs:

This finding lead to no improvement.So I fired up my logic comparators and started to probe TTLs.Sequentially I was able to locate these faulty ones, all of them on VIDEO board and from Fuitsu:

• 74LS153 @9H

 

• 74LS157 @2F

 

• 74LS244 @5W

But the board was still not booting :

Shorting some data/address lines of two 6264 SRAMs @3A and 3B changed the garbage on screen so this was the path to follow, the problem was in the tilemap generation circuit which these RAMs are part of :

Probing the RAMs revealed that the R/W lines (pin 27) of both were stuck high, according to schematics these signals come from a 74LS27 @4B:

 

My HP10529A logic comparator confirmed troubles on two outputs of this 74LS27 which failed when tested out-of-circuit:

Now board succesfully passed the self-test and entered in game fully playable with sound but all graphics had very noticeale jailbars:

Most of graphics data is stored in four 4Mbit MASK ROMs:

While dumping them my programmer reported troubles for the ones @10L and 10M:

 

Replaced them with two 27C400 EPROMs fixed the issue and board completely.

Evil Konami (and Fujitsu) defeated again but war is not over.See you to next battle…