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.

Megazone repair log #2

 PCB Repair Logs, Repair Logs  Comments Off on Megazone repair log #2
Aug 102017
 

Got this faulty pcb for my collection

 

Game was resetting over and over right after the first stating screen without even the possibility to see the diagnostic screen “RAM ROM OK”

The code was running and the watchdog was triggered by some event which I eventually found in a faulty 2114 SRAM @E15 on the video board

 

Marked in red on the actual pcb:

After changing it, the boot process went on until it displayed RAM and ROM OK but it reset again just before screen with the white grid.

At this time I was complete blind , missing any programming skills I couldn’t check what the code missed to go on.

I had a suspect on the sound part and after checking the clocks on the 8039 MCU I noticed it was completely missing.

The oscillator was working correctly and from the schematics I could see that the clock for the 8039 and the AY is generated using some 4bit binary counters 74ls293, very difficult to find on other boards.

 

Probing pin 9 of 74ls293@A12 it was stuck high while on pin 10 I had the clock.

I proceeded to test it out of circuit but was tested good.

Not sure about the reliability of the tester, I found a Starforce boot which use one 74ls293 and I installed it in a socket on megazone.

Still reset and no clock from pin 9

The output of the IC@A12 goes to pin 8 of a 74ls240, therefore I decided to test pin 8 of IC @D14 against +5V and it gave me a short.

After changing it the game finally booted without any other faults

 

Devil World repair log

 PCB Repair Logs, Repair Logs  Comments Off on Devil World repair log
Jul 212016
 

Got this Devil World PCB as non working. This game is running on a Konami Twin 16 hardware. It is a two layer board with the first one devoted to CPU/sound and the second one to GFX/video. The two faulty/replaced chips were on the video board and are highlighted in red.

devilworld1

Luckily the board was booting and got stuck on the RAM/ROM test screen with ROM #18 reported as bad (chip #1 on the board picture above).

devilworld2

That ROM is part of a 4 ROMs row which contains the GFXs. They are 40 pins Konami chips and looking in MAME I could see that they were 512kb MASK ROMs. I tried dumping it with my programmer but was unable as it found one dead pin. Compatible EPROMs for these are 27C400 so I burned one and replaced it.

The game was now booting but with a color problem on some tiles.

devilworld3 devilworld5

After a deep look at the video board I could find a Fujitsu 74LS153 located at 10H (chip #2 on the board picture above) with floating outputs (while inputs had healthy pulsing signals). I piggybacked it and got everything corrected. I desoldered the faulty one, put a socket and replaced it. Board is now working perfectly.

devilworld4 devilworld6

Bucky O’ Hare repair log #2

 PCB Repair Logs, Repair Logs  Comments Off on Bucky O’ Hare repair log #2
Jun 182016
 

Got another Konami game with the usual jail bars defect that is so common on these games

bucky3

 

I ran again the maskrom test and it reported bad maskrom 8B.

After desoldering it and testing as 27c160, the programmer complained about missing contacts on several pins.

bucky

After replacing the markrom with a 27c160, the game was 100% fixed

bucky2

 

bucky4

Sunset Riders repair log #4

 PCB Repair Logs, Repair Logs  Comments Off on Sunset Riders repair log #4
Jun 182016
 

I got this pcb for a repair.

Gameplay was fine but graphics had black lines and music had a lot of white noise.

ssrider

 

I ran the maskrom check and it reported two roms as bad, one of which was infact the rom with the sound data.

 

ssrider2

 

It doesn’t mean necessarily that the maskroms are bad, can be also that the custom chips have some pins not soldered correctly or the chips themselves being faulty.

The only way is to desolder the maskroms and check on a programmer if it reports pins not connected which means that the chip internally is broken.

After a check with the romset, I decided to dump rom 16k as 27c400 (4mbit eprom with maskrom pinout) and rom 1d as a 27c800 (8mbit 16bit eprom).

Both were reported as having pins non connected properly.

ssrider3

So I replaced maskrom 16k with a 27c400 and the markrom at 1d with a 27c160 eprom (16mbit 16bit eprom) after having doubled the original file in order to prevent the game to access the empty space in case the additional addrr line is not connected to GND or 5V.

This fixed 100% the game

ssrider4

ssrider5