I received this 1943: The Battle of Midway Mark II in the past days for dumping and repair :

Game is an unofficial US version of the 1943 Kai, probably an hack where airplane sprites are from 1943 Kai but the background is from 1943.I obviously dumped it and it has been already emulated in latest MAME 0.175 release:

The board was in good shape despite its age, it booted up too but crashed or freezed after few seconds of attract mode or after started a new play:

In the beginning I tought about some problem in code execution so I replaced the WORK RAM as well as suspicious ICs involved in Z80 address/data bus but this didn’t lead to any improvement.Testing the board with a logic probe, a logic comparator and a scope gave me the feeling like it was some kind of disturb on the board which afftected timing causing freezes and crashes.In the below video you can see how the HP10529A logic comparator detected a glitch pulse in the exact moment when the game crashes :

Also probing the clock signal of Z80 with a scope revealed some interferences in the waveform.

From my experience often a capacitor with increased ESR can inject disturb in the whole board since it can no longer filter ripple current.So I went to test the electrolytic capacitors in circuit with my ESR meter, they were all OK except the one @CC18 (9.2 Ohm measured against a typical value of 2 Ohm for a 47uF 16V)

Among other things, this capacitor is vital for main Z80 /RESET signal generation since it’s part of the typical circuit made along with a voltage monitor like the PST518 IC adopted on this board:

Once removed it, I had confirm of his increased ESR, besides also capacitance was half of its declared value:

Replacing the capacitor with a good one fixed the game completely.

In the past days I received this Nintendo VS. System for a repair:

For the uninitiated the Nintendo VS. System is an arcade platform designed for two-player competitive play using the VS. UniSystem or VS. DualSystem based on the Nintendo Entertainment System.

The system came with his special JAMMA adapter and two game ROM sets installed (Super Mario Bros and Excitebike) so time to power it up and I got this scenario:

As you can see, screen was all bluish sign that the RED component was missing.This was confirmed by probing the signal, it was stuck LOW on its source which is pin 14 of the RP2C04 PPU @8F :

The PPU chip was tested as good in another system so there was something in the path which forced the signal LOW.Before reaching the corresponding pin on edge connector, the signal is converted from digital to analog by a net of resistors and amplfied by a LM324 OP-AMP @1P:

Probing the output pin 8 of this OP-AMP I could measure only +1.4VDC against +10VDC of the output of the other one @3F which is involved in the blue color (which was correctly working)

So I decided to pull out the LM324 and add a rounded machine-tooled socket :

When tested out-of-circuit, it failed:

Fitted a new one:

and red color was restored :

No further issue were found so board 100% working.End of job.

I had since ages this untested Phoenix PCB (manufactured by Logitec Co.,Ltd so not the Taito/Centuri version but same layout of it)

Time to build the needed adapter and I powered the board up with this scenario:

All the screen was filled with a pattern of lines and dots.For first I went to dump all the ROMs on the logic board.Doing a comparison with the MAME dumps I got this result:

001.ic45: used in Phoenix (Irecsa / G.G.I Corp, set 2) renamed phoenix.46

002.ic46: used in Phoenix (Irecsa / G.G.I Corp, set 2) renamed phoenix.46

003.ic47: used in Phoenix (Irecsa / G.G.I Corp, set 2) renamed phoenix.47

004.ic48: used in Phoenix (Irecsa / G.G.I Corp, set 2) renamed 01.ic48

005.ic49: used in Phoenix (Irecsa / G.G.I Corp, set 2) renamed phoenixc.49

006.ic39: used in Phoenix (Irecsa / G.G.I Corp, set 2) renamed h6-ic50.6a

007.ic51: used in Phoenix (Irecsa / G.G.I Corp, set 2) renamed h7-ic51.7a

008.ic52: used in Phoenix (Irecsa / G.G.I Corp, set 2) renamed phoenixc.52

009.ic50: used in Phoenix (Irecsa / G.G.I Corp, set 2) renamed phoenixc.39

010.ic40: used in Phoenix (Irecsa / G.G.I Corp, set 2) renamed phoenixc.40

11.ic23: used in Phoenix (Irecsa / G.G.I Corp, set 2) renamed ic23.3d

12.ic24: used in Phoenix (Irecsa / G.G.I Corp, set 2) renamed ic24.4d

All my ROMs matched this MAME set but the two highlighted in the above list were swapped in their sockets, you can clearly notice it in the following picture :

Putting the two ROMs in right location restored the graphics but colors were wrong, here’s a comparison with a MAME screenshot on the right:

According to MAME source, low and high bits of the palette come from two bipolar ROMs @IC40 and IC41 :

I dumped them and, like the two EPROMs, they were put by someone in wrong socket:

ic40: used in Phoenix (Irecsa / G.G.I Corp, set 2) renamed mmi6301.ic41

ic41: used in Phoenix (Irecsa / G.G.I Corp, set 2) renamed mmi6301.ic40

Repositioned the BPROMs, colors came back to normal but, when I was playing the game, I noticed two further issues : shield (button two) of player 1 and 2 was not working, tracing back the involved pins from JAMMA connector I promptly found the cause:

Traces were severed, perhaps from some operator to make the game harder ( and earn more money..).I patched them with a bit of AWG30 wire:

The other issue concerned the audio, some effects (like shots and explosions) were missing replaced  by some whistling sounds:

With the help of schematics I could figure out that these sounds were generated by a 4006 shift register @IC45:

Clock were present on pin 3 when sounds were triggered but all its outputs were stuck high or low  (and totally missing on pin 10).

Since device was already socketed I tested it out-of-circuit in my BK560A where it failed:

With a good IC all the sounds were restored but, before closing this repair, I noticed that the board was randomly missing the boot staying stuck on this garbage screen :

Doing a visual inspection I noticed a missing resistor @R13 and capacitor @C2 near the 8085 main CPU :

Checking the schematics these were involved in RESET circuitry:

The service manual reported them as a 10uF tantalum capacitor and a 100Ohm resistor.:

so I promtly installed these parts :

No more missing boot and fully working board!