Corrado Tomaselli

Defender repair log #2

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Nov 302017
 

After reparing my Defender ( see this log: http://www.jammarcade.net/defender-repair-log/ ) I noticed that the screen had some horizontal lines of different brightness.

At first I didn’t give much attention but then I decided to look at this issue deeper.

Moving the screen left and right with the monitor commands I noticed these defects:

 

 

Having the experience of a similar problem on my Burnin Rubber ( http://www.jammarcade.net/burnin-rubber-repair-log/ ), to me it was clear there was a video blanking problem

With the schematics in hand I found this circuit:

Signals from 7420@5C were good so I started probing the 7400@4B

 

All signals were good except that pin 10 was floating.

Looking at the above mentioned schematics, pin 10 is tied to the nearby pin 11!

I checked the board and found out that actually the pcb has no trace connected the 2 pins togheter!

 

No broken traces, it is actually simply not there!

I connected the two pins and…..

 

Game fixed!

Now I am wondering if my CPU board revision has a production error.

Searching on internet I haven’t found a similar problem therefore I would like to have a feedback from other owners of Defender if their pcbs has the trace or not.

Liquid Kids repair log #2

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Nov 302017
 

Received this Japanese version of Liquid Kids for a repair  running on a different F2 hardware.

 

The game was playing fine but hadn’t any sounds.

Amplifier and preamps were good so I started to probe the sound circuit logic.

The Z80 sound cpu ram had some weak signals

After replacing it , the sound was restored.

Haunted Castle repair log #5

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Nov 252017
 

I got this board for my collection as untested from an arcade operator

Board was the typical Konami pcb manufactured in Italy ( I believe Electronic Devices had a deal with them to import the pcbs and populate certain chips in Italy).

You regognize these boards because they have sound z80 made in Italy , soldered eproms and cheap sound potentiometer

Later on, beginning of 90s they started to put also general “E.Devices” stickers on eproms in place of Konami ones, but at least the eproms were socketed

Back to this board, it booted and the graphic was OK but there was a continuous metallic sound all the time.

Ruled out DAC and OP AMPS because usually when these fails, you have at least either FM or samples working, I started to probe the sound circuit logic following the schematics.

I noticed that the commands from the main CPU were correctly sent to the sound section but as soon as the Z80 had an INTERRUPT request, the CPU didn’t aknowledge it and blocked itself

In particular:

 

Signal IORQ didn’t go low, thus making the INT signal from the 74LS74 always LOW.

I proceeded to desolder the Z80 and tested it on another game with a socketed CPU and it confirmed to be bad.

While soldering the same Z80 by NEC used on proper Konami assembled boards, I also changed the sound potentiometer with an original Konami taken from another scrap game.

 

Game was fixed without any other issues.

Pac-Mania repair log #2

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Nov 092017
 

I bought a faulty Pac-Mania mainly for spare parts but I gave him a chance and tried to repair it

The game was missing sound roms, after replacing them, game booted and you could play but the screen was totally a mess.

After some blind testing I started test all socketed custom chips and rams against new ones and I eventually found the culprit

in the “text” ram @L5!

It was so bad that it totally covered the screen with junk graphics

Replacing it fixed the game 100%

Pacland repair log

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Nov 092017
 

Got this Pacland, Sidam version, in mint conditions  for a repair

The game had some color bitplanes of the sprites shifted to the left as you can see from this pic

The sprites are handled by CUS29 and there are two 2149 rams connected.

Piggybacking a good 2149 ram on top of the one @3T restored good colours

Testing it out of circuit confirmed it was bad

The game had no other faults and was 100% fixed