myPinballs
Member
So i'm starting another repair, after fixing the TMHT pcb. This time a midway Mortal Kombat 2 pcb. These boards are going to be additional games i can play when i find an original r-type cabinet and board 
So this board was part of a few pcbs i picked up this week. The others were capcom cps era.
This board appears to be dead. I've been messing about with it on and off over the last few days. This is what i get when powering on
Then after a few seconds the screen goes blank and i never get to the handy cpu board test screen
Bloomin annoying.
Board is in good condition. No corrosion or previous repairs afaict.
Board is the later version, with the 8mb roms so no need for the memory expansion card. I have removed the sound card for now to. Checked the voltages and am sure i have a good solid 5v, ground and 12v coming in to the board.
Burned a new set of revision game roms even thought he originals checksumed ok. No change.
Probed the clock lines. All ok.
Probed the voltage and reset monitor ic. Reset line goes high for a few seconds and then goes low and high and repeats over and over, which is in time with the second Board led (DS3). The issue seems to be the watchdog line never pulses. So i'm guessing something is causing a cpu or custom asic crash. If you add a pulse to the watchdog line then it doesn't reset but still does not boot. So i'm thinking the monitor ic is ok.
Anyone have any ideas what's needed to get to the cpu test screen? Judging by whats on the screen, the custom asic seems the be the main ic, as the cpu is shown on screen as a test item. I haven't found any issues with the revision game roms. All address and data lines and enable lines are present and pulsing though.
I did think of a possible option, as there are 4 ram ics which are part of the cpu section, and 2 of them on this board are Fujitsu brand (from experience with konami i suspected these may be an issue) but they actually appear in the cpu test as 'scratch ram' tests so my logic says these can't stop the test screen appearing if they are tested after it displays.
Brain ache!!
So this board was part of a few pcbs i picked up this week. The others were capcom cps era.
This board appears to be dead. I've been messing about with it on and off over the last few days. This is what i get when powering on
Then after a few seconds the screen goes blank and i never get to the handy cpu board test screen
Board is in good condition. No corrosion or previous repairs afaict.
Board is the later version, with the 8mb roms so no need for the memory expansion card. I have removed the sound card for now to. Checked the voltages and am sure i have a good solid 5v, ground and 12v coming in to the board.
Burned a new set of revision game roms even thought he originals checksumed ok. No change.
Probed the clock lines. All ok.
Probed the voltage and reset monitor ic. Reset line goes high for a few seconds and then goes low and high and repeats over and over, which is in time with the second Board led (DS3). The issue seems to be the watchdog line never pulses. So i'm guessing something is causing a cpu or custom asic crash. If you add a pulse to the watchdog line then it doesn't reset but still does not boot. So i'm thinking the monitor ic is ok.
Anyone have any ideas what's needed to get to the cpu test screen? Judging by whats on the screen, the custom asic seems the be the main ic, as the cpu is shown on screen as a test item. I haven't found any issues with the revision game roms. All address and data lines and enable lines are present and pulsing though.
I did think of a possible option, as there are 4 ram ics which are part of the cpu section, and 2 of them on this board are Fujitsu brand (from experience with konami i suspected these may be an issue) but they actually appear in the cpu test as 'scratch ram' tests so my logic says these can't stop the test screen appearing if they are tested after it displays.
Brain ache!!
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