Corrado Tomaselli

No background in electronics. Learned everything by reading pdf books and expecially Video game logic Vol 1 by Atari and in general early Atari and Williams arcade manuals

Zaxxon / Future Spy flip screen hack

Guides, Mods 2 Responses »

Mar 292016

Sometimes it is very annoying when you have placed your arcade monitor vertically and certain games are shown upside down and even worse they have no option to flip the screen.

It happens very often with older games but sometimes even with newer games from the 90s.

In these cases you have 2 options: reverse phisically your monitor or reverse the yoke on the pcb of the monitor (not very safe).

Now I show you a new option available only when the games were also prepared for cocktail tables (that means they have already the circuit to flip the screen for the second player)

In this first “flip screen” hack I will take Zaxxon / Future Spy hardware as an example

Future Spy_2

These games have no flip screen option but they have the preparation for cocktail tables play.

The board is very big but luckily schematics are available and they are very clear to understand.

The hack is very simple: input nr.4 of 74ls367@U64 is normally LOW for first player game and HI for second player game.

We have only to force pin 4 to HI (+5V) using a wire so that the screen is always flipped as it was playing the second player even in upright mode.

Zaxxo_flip screen hack

Very simple and effective!

Megazone repair log #1

PCB Repair Logs, Repair Logs 3 Responses »

Mar 292016

Got a very clean Megazone pcb for a repair. The board was in near mint conditions but it didn’t boot and also the Sync was missing.

Looking at the schematics available online, I noticed that the quartz responsibile for the CPU clock and sync was the one placed on the bottom board.

Tested with my frequency meter and it was dead.

It is a very rare 18.432mhz OSC which to my knowledge is used only by early 80s Konami boards.

megazone

Luckily I had a Double Dribble which I used for spare parts which had the very same OSC.

After changing it, the game booted perfectly.

megazone3

megazone4

For you information, if you try to install the more common 20Mhz OSC, the colours are off and the scrolling is jumping often, so unfortunately it’s not a good replacement.

The board had no sound but I immediately noticed that there was no noise coming out of the speaker which is the evidence of a faulty amplifier.

The amplifier is infact the very unrielable LA4460N, so after confirming the the music could be hear on input pin 2 , I exchanging it and fixed completely the game.

megazone2

X-Men repair log #2

PCB Repair Logs Comments Off

Mar 242016

The board played completely blind.

With a logic probe I tested all the 74Ls07 which had fixed input and outputs as expected, therefore no activity at all.

Tested the clock (pin 11) on the 74LS273@9C and 10C and it was fixed high.

xmen-schems

Unfortunately the schematics of the game found in internet are not complete, so I had to trace back manually and found out that the output pin 14

of the 74LS04@17E was stuck, while the input was floating.

xmen

Replacing the chip with a good known one didn’t fix the problem!

So I looked on the back of the pcb and found that a pin of a chip was touching the line of the output it shorted it !

After lifting the pin, the pcb showed the game in colours but all the screen was blocky.

While searching for the source of the problems I shorted two pins of a custom chip by mistake and the pcb rebooted without any issues.

It was clear it was some kind of reset problem for the graphic chips.

The 68000 had it’s own circuit but the customs had a separate reset.

Looking back on the schematics, I found out that the system reset was given by the custom 051550 which I couldn’t find on the board….

Infact it was missing and I didn’t notice!

Soldered a new one from a scrap pcb and the game was fully restored!

xmen2

Pang repair log #3

PCB Repair Logs, Repair Logs Comments Off

Mar 232016

I desuicided this original PCB but after booting up I got this

Pang Pang2

After checking rams and buffer they were all good.

Just to avoid any doubts I dumped without convinction all the graphics eproms which normally are very reliable.

To my surprise when I lifted eprom PWE02 with the pcb in operation, the parts of the background corrupted turned to black revealing that at least the problem was connected to the circuit around the eprom.

Placing the eprom on my programmer I got this:

Foto 20-03-16 10 00 58