A friend got a Mahou Daisakusen (japanese version of Sorcer Striker) board with faulty graphics.
It was playing fine with sound but there was an obvious color palette problem.
I started looking at signals around the color outputs of the PCB and quickly found weak signals on the 74HCT273 at location U12. Piggybacking the chip with a working 74LS273 fixed the colors immediately.
I replaced the chip… Board fixed.
Here is a picture of the PCB with the defective chip highlighted in red:
We have some new dumps from an unusual arcade hardware called High Rate DVD, a DVD-based mahjong system released by Nichibutsu in different volumes, you can read more about here:
256KB binary dumps have been provided by ‘system11’ on Dumping Union list, I took care of reversing them to GAL16V8 targeting devices.Each PAL (identified by a colored stripe or dot on chip) is shared among more than a volume and other Mahjong games too, you will find info on database.Thanks to ‘system11 who also successfully tested dumps back on hardware.
New PAL dumps today.We have the ones from :
Received some Irem 92 boardsets mostly for replacing preventively the infamous ELNA brown electrolytic capacitors but two of them were faulty too.
The first was a Cross Blades (japanese version of Blade Master!), board had green ELNA capacitors so no strict need to replace them.
But it suffered from sprites isssue, they were missing some parts:
Pressing the board in the area of ‘NANAO GA22’ custom ASIC restored the sprites :
A closer inspection of this custom revealed three liften pins :
Reflowed them fixed the issue :
The second board was Hook (World version) :
Game booted up but sound was missing, I could hear only a rustling noise.Besides, video had some interferences:
Usually the two issues are strictly related, the cause is some bad electrolytic capacitor in audio circuit which affects video output too.The board mounted ELNA brown capacitors which are well known to age poorly.Sure enough :
The 470uF 25V @C202 was clearly leaking, this capacitor is used as filter for the +12V for the amplifier, this explained the issue.Measuring it out of circuit confirmed it was bad with an increased ESR of 150 Ohm :
I replaced this and all other electrolytic capacitors, this fixed board completely:
Here’s for reference the capacitors list with value and location :
C201 1uF 50V
C202 470 uF 25V
C203 220uF 10V
C204 22uF 25V
C209 100uF 25V
C210 1uF 50V
C213 47uF 16V
C215 1uF 50V
C216 1uF 50V
C217 1uF 50V
C218 1uF 50V
C219 1uF 50V
C236 100uF 25V
You can find it in our document section too :
https://www.jammarcade.net/files/Documents/Irem_’M92-A-B’_CPU_board_electrolytic_capacitors_list.pdf
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
